<p><strong> .3UNIT 2: NITROGEN AND ITS COMPOUNDS.</strong></p>
<p><strong>Unit checklist.</strong></p>
<ol>
<li>Introduction</li>
<li>Preparation of nitrogen</li>
</ol>
<ul>
<li>Isolation from air</li>
<li>Isolation from liquid air</li>
<li>Laboratory preparation</li>
<li>Preparation from ammonia</li>
<li>Properties of nitrogen</li>
<li>Oxides of nitrogen
<ul>
<li>Nitrogen (I) oxide</li>
<li>Nitrogen (II) oxide</li>
<li>Nitrogen (IV) oxide</li>
</ul>
</li>
</ul>
<ol start="3">
<li>Action of heat on nitrates.</li>
<li>Ammonia gas</li>
</ol>
<ul>
<li>Preparation</li>
<li>Laboratory preparation</li>
<li>Preparation from caustic soda</li>
<li>Test for ammonia</li>
<li>Fountain experiment</li>
<li>Properties and reactions of ammonia</li>
<li>Large scale manufacture of ammonia gas: the Haber process</li>
<li>Uses of ammonia</li>
</ul>
<ol start="5">
<li>Nitric (V) acid</li>
</ol>
<ul>
<li>Laboratory preparation</li>
<li>Industrial manufacture of nitric (V) acid: The OtswaldÂs process.</li>
<li>Reactions of dilute nitric acid</li>
<li>Reactions of concentrated nitric acid</li>
<li>Uses of nitric acid</li>
</ul>
<ol start="6">
<li>Test for nitrates.</li>
<li>Pollution effects of nitrogen and its compounds</li>
<li>Reducing pollution environmental pollution by nitrogen compounds.</li>
</ol>
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<p><strong>Introduction:</strong></p>
<p>&#8211; About 78% of air is nitrogen, existing as N<sub>2</sub> molecules.</p>
<p>&#8211; The two atoms in the molecules are firmly held together.</p>
<p>&#8211; Nitrogen does not take part in many chemical reactions due to its low reactivity.</p>
<p>&#8211; Its presence in air dilutes oxygen and slows down respiration, burning and rusting.</p>
<p> ;</p>
<p><strong>Preparation of nitrogen.</strong></p>
<p><strong>(a). Isolation from air.</strong></p>
<p><strong>(i). Apparatus.</strong></p>
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<p><strong>(ii). Procedure.</strong></p>
<p>&#8211; Air is driven out of the aspirator by passing water into the aspirator from a tap.</p>
<p>&#8211; The air is the passed through a wash bottle containing concentrated potassium hydroxide solution.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; To remove carbon (IV) oxide from air.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>2KOH<sub>(aq)</sub> + CO<sub>2(g)</sub> K<sub>2</sub>CO<sub>3(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>Then</p>
<p>K<sub>2</sub>CO<sub>3(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + CO<sub>2(g) </sub> 2KHCO<sub>3(aq)</sub></p>
<p> ;</p>
<p>Thus;</p>
<p>KOH<sub>(aq)</sub> + CO<sub>2(g)</sub> KHCO<sub>3(aq)</sub></p>
<p> ;</p>
<p>&#8211; The carbon (IV) oxide-free air is then passed into a combustion tube with heated copper metal.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; To remove oxygen from the air.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>In this reaction the brown copper metal is oxidized to black copper (II) oxide.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2Cu<sub>(s)</sub> + O<sub>2(g) </sub> 2CuO<sub>(s)</sub></p>
<p><strong><em>Brown Black</em></strong></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Alternatively oxygen can be removed by passing the carbon (IV) oxide-free air through pyrogallic acid.</p>
<p>&#8211; The remaining part of air is mainly nitrogen and is collected over water.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Nitrogen obtained by this method contains noble gases like xenon, argon etc as impurities.</p>
<p>&#8211; Purer nitrogen may be obtained by heating ammonium nitrite.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>NH<sub>4</sub>NO<sub>3(s)</sub> <strong><em><sup>Heat</sup></em></strong> N<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(g)</sub></p>
<p> ;</p>
<p><strong>Summary.</strong></p>
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<p><strong>(b). Removal from liquid air.</strong></p>
<p>&#8211; Liquid air is primarily a mixture of nitrogen and oxygen with small amounts of noble gases.</p>
<p>&#8211; This method involves manufacture of liquid air and consequent fractional distillation.</p>
<p> ;</p>
<p><strong>The chemical process.</strong></p>
<p><strong>Step 1: removal of dust particles.</strong></p>
<p>&#8211; Dust particles are first removed by either of the two processes:</p>
<ul>
<li>Electrostatic precipitation</li>
<li></li>
</ul>
<p><strong>(i). Electrostatic precipitation:</strong></p>
<p>&#8211; Air is passed through oppositely charged plates hence an electric field.</p>
<p>&#8211; Dust particles (charged) are consequently attracted to plates of opposite charges.</p>
<p> ;</p>
<p><strong>Diagram: electrostatic precipitation:</strong></p>
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<p><strong>(ii). Filtration:</strong></p>
<p>&#8211; The air is passed through a series of filters which traps dust particles as the air is forced through.</p>
<p> ;</p>
<p><strong>Step 2: removal of carbon (IV) oxide.</strong></p>
<p>&#8211; The dust-free air is passed through a solution of potassium hydroxide; to remove carbon (IV) oxide.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>2KOH<sub>(aq)</sub> + CO<sub>2(g)</sub> K<sub>2</sub>CO<sub>3(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>Then:</p>
<p>K<sub>2</sub>CO<sub>3(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + CO<sub>2(g)</sub> 2KHCO<sub>3(aq)</sub></p>
<p><strong><em>(Excess)</em></strong></p>
<p>&#8211; Alternatively, sodium hydroxide may be used in place of potassium hydroxide.</p>
<p> ;</p>
<p><strong>Step 3: Removal of water vapour.</strong></p>
<p>&#8211; The dustless, carbon (IV) oxide-free air is next passed into a chamber with <strong>concentrated sulphuric acid</strong> or <strong>anhydrous calcium chloride</strong> in which water vapour is separated and removed.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>To remove water vapour, air may be alternatively passed into a <strong>freezing chamber</strong> where it is condensed at -25<sup>o</sup>C.</p>
<p>&#8211; The water vapour <strong>solidifies</strong> and is then absorbed by <strong>silica gel</strong> and separated out.</p>
<p>&#8211; Air is freed from carbon (IV) oxide, water vapour and dust particles (before compression) so as to prevent <strong>blockage</strong> of the pipes caused by solid materials at liquefaction temperatures i.e. carbon (IV) oxide and water vapour form solids which may block the collection pipes.</p>
<p> ;</p>
<p><strong>Step 4: Liquification of air.</strong></p>
<p>&#8211; The air free from dust, carbon (IV) oxide and water vapour is then compressed at about 200 atmospheres, cooled and allowed to expand through fine jet.</p>
<p>&#8211; This sudden expansion causes further cooling and the gases eventually liquefy.</p>
<p>&#8211; The liquid is tapped off through a valve while gas which has escaped liquefaction returns to the compressor.</p>
<p>&#8211; Liquid air is a transparent <strong>pale blue liquid</strong>.</p>
<p>&#8211; This liquid is then fractionally distilled.</p>
<p> ;</p>
<p><strong>Step 5: Fractional distillation of liquid air.</strong></p>
<p>&#8211; The boiling point of nitrogen is -196<sup>o</sup>C (77K) and that of oxygen is -183<sup>o</sup>C (90K).</p>
<p>&#8211; Consequently when liquid air is allowed to warm up, the nitrogen boils off first and the remaining liquid becomes richer in oxygen.</p>
<p>&#8211; The top of the fractionating column is a few degrees cooler than the bottom.</p>
<p>&#8211; Oxygen, the liquid with the higher boiling point (-183<sup>o</sup>C) collects at the bottom as the liquid.</p>
<p>&#8211; The gas at the top of the column is nitrogen which ahs a lower boiling point.</p>
<p>&#8211; The more easily vapourised nitrogen is taken off.</p>
<p>&#8211; This way about 99.57% nitrogen is obtained.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; The separation of nitrogen and oxygen from air is a proof that air is a mixture and not a compound.</p>
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<p><strong>Summary: Fractional distillation of liquid air.</strong></p>
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<td><strong>AIR</strong></td>
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<p>Step 1: Elimination of dust by Filtration</p>
<p>and electrostatic precipitation</p>
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<p>Step 2: CO<sub>2</sub> removal, pass dust free air</p>
<p>through KOH or NaOH</p>
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<p>Step 3: Removal of water vapour; through</p>
<p>condensation -25<sup>o</sup>C) or conc. H<sub>2</sub>SO<sub>4</sub></p>
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<p><strong><em>Recycling</em></strong> Step 4: Compression at approximately 200</p>
<p>atmospheres; cooling and expansion of air</p>
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<p>Step 5: Fractional distillation</p>
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<p><strong>(c). Laboratory preparation method.</strong></p>
<p><strong>(i). Apparatus.</strong></p>
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<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Concentrated solutions of sodium nitrite and ammonium chloride are heated together in a round bottomed flask.</p>
<p> ;</p>
<p><strong>(iii). Observations.</strong></p>
<p>&#8211; Colourless gas (nitrogen) is evolved rapidly and is collected over water.</p>
<p> ;</p>
<p><strong>(iv). Equation.</strong></p>
<p>NaNO<sub>2(aq)</sub> + NH<sub>4</sub>Cl<sub>(aq)</sub> <sup>heat</sup> NaCl<sub>(aq)</sub> + N<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l).</sub></p>
<p><sub> </sub></p>
<p><strong>Note:</strong> the resultant gas is less dense than that isolated from air.</p>
<p><strong>Reason: </strong></p>
<p>&#8211; It does not contain impurities.</p>
<p> ;</p>
<p><strong>(d). Preparation from ammonia.</strong></p>
<p><strong>(i). Apparatus.</strong></p>
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<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Dry ammonia gas is passed over a heated metal oxide e.g. copper metal.</p>
<p>&#8211; The <strong>metal oxide</strong> is r<strong>educed</strong> to the metal while <strong>ammonia gas</strong> is itself <strong>oxidized</strong> to <strong>nitrogen</strong> and <strong>water</strong>.</p>
<p>&#8211; Water is condensed and collected in a u-tube immersed in ice cubes.</p>
<p>&#8211; Nitrogen produced is collected <strong>over water</strong>.</p>
<p> ;</p>
<p>(iii). Observations and explanations.</p>
<ul>
<li><strong>Copper (II) oxide:</strong></li>
</ul>
<p>3CuO<sub>(s)</sub> + 2NH<sub>3(g)</sub> 3Cu<sub>(s)</sub> + N<sub>2(g)</sub> + 3H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(Black) (Brown) (Colourless)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>Zinc (II) oxide</strong></li>
</ul>
<p>3ZnO<sub>(s)</sub> + 2NH<sub>3(g)</sub> 3Zn<sub>(s)</sub> + N<sub>2(g)</sub> + 3H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(Yellow-hot) (Grey) (Colourless)</em></strong></p>
<p><strong><em>(White-cold)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>Lead (II) oxide</strong></li>
</ul>
<p>3PbO<sub>(s)</sub> + 2NH<sub>3(g)</sub> 3Cu<sub>(s)</sub> + N<sub>2(g)</sub> + 3H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(Red-hot) (Grey) (Colourless)</em></strong></p>
<p><strong><em>(Yellow-cold)</em></strong></p>
<p><strong><em> </em></strong></p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong>Properties of nitrogen.</strong></p>
<p><strong>(a). Physical properties.</strong></p>
<ol>
<li>It is a colourless, odourless and tasteless gas; almost completely insoluble in water.</li>
<li>Slightly lighter than air.</li>
</ol>
<p> ;</p>
<p><strong>(b). Chemical properties.</strong></p>
<ol start="3">
<li>It is inert (unreactive)</li>
</ol>
<p><strong>Reason:</strong></p>
<p>&#8211; The inert nature of nitrogen is due to the strong covalent bonds between the two nitrogen atoms in the molecule; N<sub>2</sub>.</p>
<p> ;</p>
<p><strong>Structurally;</strong></p>
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<p>&#8211; In air, it neither burns nor supports combustion and acts mainly as a diluent for the oxygen; slowing down the rate of burning.</p>
<p> ;</p>
<p><strong>Chemical test for nitrogen.</strong></p>
<p>&#8211; A gas is proved to be nitrogen by elimination: &#8211;</p>
<ul>
<li>It extinguishes a lighted splint and dos not burn; hence it is not oxygen, hydrogen or carbon (II) oxide.</li>
<li>It has neither <strong>smell</strong> nor <strong>colour</strong>; and therefore is not chlorine, ammonia, sulphur (IV) oxide or hydrogen chloride.</li>
<li>It does not form a <strong>white precipitate</strong> in lime water, and so it is not carbon (IV) oxide.</li>
<li>It is <strong>neutral</strong> to litmus and therefore cannot be carbon (IV) oxide, hydrogen sulphide, ammonia, hydrogen chloride</li>
</ul>
<p> ;</p>
<ol start="4">
<li><strong> Reaction with hydrogen.</strong></li>
</ol>
<p>&#8211; Under special conditions (i.e. high pressure, low temperatures and presence of iron catalyst), nitrogen combines with hydrogen to produce ammonia.</p>
<p><strong>Equation:</strong></p>
<p>N<sub>2(g)</sub> + 3H<sub>2(g)</sub> 2NH<sub>3(g)</sub></p>
<p> ;</p>
<p>&#8211; This reaction forms the basis of <strong>Haber process</strong> used in the manufacture of ammonia.</p>
<p> ;</p>
<ol start="5">
<li><strong> Reaction with burning magnesium.</strong></li>
</ol>
<p><strong>(i). Apparatus.</strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
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<p><strong> </strong></p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; A piece of burning magnesium ribbon is introduced into a gas jar full of nitrogen.</p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; The magnesium ribbon continues to burn and a <strong>white solid</strong>; magnesium nitride is formed.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>3Mg<sub>(s)</sub> + N<sub>2(g)</sub> <sup>Heat</sup> Mg<sub>3</sub>N<sub>2(s)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; When magnesium nitride is treated with water or a solution of sodium hydroxide; the characteristic pungent smell of ammonia can be detected.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p><strong>In water</strong></p>
<p>Mg<sub>3</sub>N<sub>2(s)</sub> + 6H<sub>2</sub>O<sub>(l)</sub> 2NH<sub>3(g)</sub> + 3Mg(OH)<sub>2(aq)</sub></p>
<p> ;</p>
<p><strong>In sodium hydroxide:</strong></p>
<p>Mg<sub>3</sub>N<sub>2(s)</sub> + NaOH<sub>(aq) </sub></p>
<p> ;</p>
<ol start="6">
<li><strong> Reaction with oxygen.</strong></li>
</ol>
<p>&#8211; When nitrogen and oxygen in air are passed through an electric arc small quantities of nitrogen (II) oxide are formed.</p>
<p><strong>Equation:</strong></p>
<p>N<sub>2(g)</sub> + O<sub>2(g)</sub> 2NO<sub>(g)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Nitrogen reacts with oxygen under various conditions to give different types of nitrogen oxides.</p>
<p> ;</p>
<p><strong>Uses of nitrogen</strong></p>
<ol>
<li>Used in the <strong>Haber process</strong> in the manufacture of <strong>ammonia.</strong></li>
<li>Due to its <strong>inert nature</strong>, it is mixed with argon to fill electric bulbs (to avoid soot formation).</li>
<li>In liquid state it is used as an inert <strong>refrigerant</strong> e.g. storage of semen for artificial insemination.</li>
<li>Due to its <strong>inert nature</strong>, it is used in food preservation particularly for canned products i.e. it prevents combination of oxygen and oil which tends to enhance rusting.</li>
<li>It is used in oil field operation called enhanced oil recovery where it helps to force oil from subterranean deposits.</li>
</ol>
<p> ;</p>
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<p><strong>Oxides of nitrogen.</strong></p>
<p>&#8211; The three main oxides of nitrogen are:</p>
<ul>
<li>Nitrogen (I) oxide, N<sub>2</sub>O</li>
<li>Nitrogen (II) oxide, NO</li>
<li>Nitrogen (IV) oxide, NO<sub>2</sub></li>
</ul>
<p> ;</p>
<ol>
<li><strong> Nitrogen (I) oxide.</strong></li>
</ol>
<p><strong>Preparation of nitrogen (I) oxide, N2O</strong></p>
<p><strong>(i). Apparatus.</strong></p>
<p> ;</p>
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<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Ammonium nitrate is gently heated in a boiling tube and gas produced collected over warm water.</p>
<p>&#8211; Heating is stopped while excess ammonium nitrate still remains.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; To avoid chances of an <strong>explosion.</strong></p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; The solid (ammonium nitrate) <strong>melts </strong>and gives off nitrogen (I) oxide which is collected over <strong>warm water.</strong></p>
<p><strong>Reasons:</strong></p>
<p>&#8211; Nitrogen (I) oxide is <strong>slightly soluble</strong> in cold water.</p>
<p> ;</p>
<p><strong>(iv). Equation:</strong></p>
<p>NH<sub>4</sub>NO<sub>3(s)</sub> <sup>Heat</sup> NO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Properties:</strong></p>
<ol>
<li>It is a colourless gas, denser than air, fairly soluble in cold water and neutral to litmus.</li>
<li>It supports combustion by <strong>oxidizing </strong>elements like sulphur, magnesium and phosphorus under strong heat.</li>
</ol>
<p><strong>Equations:</strong></p>
<p>N<sub>2</sub>O<sub>(g)</sub> + Mg<sub>(s)</sub> <sup>Heat</sup> MgO<sub>(s)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<p>2N<sub>2</sub>O<sub>(g)</sub> + S<sub>(s)</sub> <sup>Heat</sup> SO<sub>2(g)</sub> + 2N<sub>2(g)</sub></p>
<p> ;</p>
<p>2N<sub>2</sub>O<sub>(g)</sub> + C<sub>(s)</sub> <sup>Heat</sup> CO<sub>2(g)</sub> + 2N<sub>2(g)</sub></p>
<p> ;</p>
<p>5N<sub>2</sub>O<sub>(g)</sub> + 2P<sub>(s)</sub> <sup>Heat</sup> P<sub>2</sub>O<sub>5(g)</sub> + 5N<sub>2(g)</sub></p>
<p> ;</p>
<ol start="3">
<li>Magnesium <strong>decomposes</strong> the gas and continues to burn in it.</li>
</ol>
<p><strong>Equation:</strong></p>
<p>N<sub>2</sub>O<sub>(g)</sub> + Mg<sub>(s)</sub> <sup>Heat</sup> MgO<sub>(s)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<ol start="4">
<li>When exposed over red-hot finely divided copper it is reduced to <strong>nitrogen</strong>.</li>
</ol>
<p><strong>Equation:</strong></p>
<p>N<sub>2</sub>O<sub>(g)</sub> + Cu<sub>(s)</sub> <sup>Heat</sup> CuO<sub>(s)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<ol start="5">
<li>Chemical test.</li>
</ol>
<ul>
<li>It <strong>relights</strong> a glowing splint.</li>
</ul>
<p><strong>Note:</strong></p>
<ul>
<li>It can be distinguished from oxygen by the following tests:</li>
</ul>
<ul>
<li>It has a <strong>sweet sickly smell</strong>; oxygen is odourless.</li>
<li>It will not give <strong>brown fumes</strong> (NO<sub>2</sub>) with nitrogen (II) oxide; oxygen does.</li>
<li>It is <strong>fairly soluble</strong> in cold water; oxygen is insoluble.</li>
<li>It extinguishes feebly burning <strong>sulphur</strong>; oxygen does not.</li>
</ul>
<p> ;</p>
<p><strong>Uses of nitrogen (I) oxide.</strong></p>
<p>&#8211; It was formerly used in hospitals as an <strong>aesthetic</strong> for <strong>dental surgery</strong> but has since been discontinued due to availability of more efficient anaesthetics.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Nitrogen (I) oxide is also called <strong>laughing gas</strong>; because patients regaining consciousness from its effects may laugh hysterically.</p>
<p> ;</p>
<ol start="2">
<li><strong> Nitrogen (II) oxide, NO.</strong></li>
</ol>
<p><strong>Preparation:</strong></p>
<p><strong>(i). Apparatus.</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Action of heat on 50% concentrated nitric acid on copper turnings.</p>
<p>&#8211; Not any heat is required.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>3Cu<sub>(s)</sub> + 8HNO<sub>3(aq)</sub> 3Cu(NO<sub>3</sub>)<sub>2(aq)</sub> + 4H<sub>2</sub>O<sub>(l)</sub> + 2NO<sub>(g)</sub></p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; An <strong>effervescence </strong>occurs in the flask; with <strong>brown fumes</strong> because the nitrogen (II) oxide produced reacts with oxygen of the air in the flask to form a brown gas, nitrogen (IV) oxide.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2NO<sub>(g)</sub> + O<sub>2(g)</sub> 2NO<sub>2(g)</sub></p>
<p><strong><em>Colourless Colourless Brown</em></strong></p>
<p> ;</p>
<p>&#8211; The brown fumes eventually disappear and the gas collected over water.</p>
<p>&#8211; The NO<sub>2</sub> fumes dissolve in the water in the trough, resulting into an acidic solution of nitrous acid.</p>
<p>&#8211; The residue in the flask is a <strong>green</strong> solution of <strong>copper (II) nitrate</strong>.</p>
<p>&#8211; Industrially, the gas is obtained when ammonia reacts with oxygen in the presence of platinum catalyst.</p>
<p>&#8211; This is the first stage in the production of nitric acid.</p>
<p> ;</p>
<p><strong>(v). Properties.</strong></p>
<ol>
<li>It is a colourless, <strong>insoluble</strong> and <strong>neutral</strong> to litmus. It is also slightly denser than air.</li>
<li>Readily combines with oxygen in air and forms brown fumes of nitrogen (IV) oxide.</li>
<li>Does not support combustion except in the case of <strong>strongly burning magnesium</strong> and <strong>phosphorus</strong>; which continues to burn in it, thereby reducing it i.e. it is an oxidizing agent.</li>
</ol>
<p> ;</p>
<p><strong>Example:</strong></p>
<p>2Mg<sub>(s)</sub> + 2NO<sub>(g)</sub> 2MgO<sub>(s)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<p>4P<sub>(s)</sub> + 10NO<sub>(g)</sub> 2P<sub>2</sub>O<sub>5(s)</sub> + 5N<sub>2(g)</sub></p>
<p> ;</p>
<ol start="4">
<li>When passed over red-hot finely divided copper, it is reduced to nitrogen gas.</li>
</ol>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2Cu<sub>(s)</sub> + 2NO<sub>(g)</sub> 2CuO<sub>(s)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<ol start="5">
<li><strong> Reaction with iron (II) sulphate.</strong></li>
</ol>
<p>&#8211; When iron (II) sulphate solution (freshly prepared) is poured into a gas jar of nitrogen (II) oxide, a dark brown colouration of <strong>Nitroso-iron (II) sulphate is obtained</strong>.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>FeSO<sub>4(aq)</sub> + NO<sub>(g)</sub> FeSO4.NO<sub>(aq)</sub></p>
<p><strong><em>Green solution Dark brown </em></strong></p>
<p><strong><em> (Nitroso-iron (II) sulphate/ nitrogen (II) oxide iron (II) sulphate complex)</em></strong></p>
<p> ;</p>
<ol start="6">
<li><strong> It is also a reducing agent.</strong></li>
</ol>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>Cl<sub>2(g)</sub> + 2NO<sub>(g)</sub> 2ClNO<sub>(l)</sub></p>
<p><strong><em>Chloro nitrogen (II) oxide.</em></strong></p>
<p> ;</p>
<ol start="7">
<li><strong> Reaction with hydrogen.</strong></li>
</ol>
<p>&#8211; When electrically sparked with hydrogen, NO is reduced to <strong>nitrogen.</strong></p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2H<sub>2(g)</sub> + 2NO<sub>(g)</sub> 2H<sub>2</sub>O<sub>(l)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Chemical test:</strong></p>
<p>&#8211; When exposed to air, nitrogen (II) oxide forms brown fumes of nitrogen (IV) oxide.</p>
<p> ;</p>
<p><strong>Uses of Nitrogen (II) oxide.</strong></p>
<p><strong>Note: &#8211;</strong>It is not easy to handle owing to its ease of <strong>oxidation.</strong></p>
<ol>
<li>It is an intermediate material in the manufacture of nitric acid</li>
</ol>
<p> ;</p>
<ol start="3">
<li><strong> Nitrogen (IV) oxide.</strong></li>
</ol>
<p><strong>Preparation:</strong></p>
<p><strong>(i). Apparatus.</strong></p>
<p><strong> </strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Action of conc. Nitric acid on copper metal.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Cu<sub>(s)</sub> + 4HNO<sub>3(l)</sub> Cu(NO<sub>3</sub>)<sub>2(aq)</sub> + 2NO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; NO<sub>2</sub> is also prepared by the action of heat on <strong>nitrates of heavy metals</strong> like lead nitrate.</p>
<p>&#8211; NO<sub>2</sub> is given off together with <strong>oxygen</strong> when nitrates of heavy metals are heated.</p>
<p>&#8211; It is best prepared by heating <strong>lead (II) nitrate</strong> in a hard glass test tube.</p>
<ul>
<li>Lead (II) nitrate is the most suitable because it crystallizes without <strong>water of crystallization</strong> (like other nitrates) which would interfere with preparation of nitrogen (IV) oxide that is <strong>soluble</strong> in water.</li>
</ul>
<p>&#8211; The gas evolved passes into a U-tube immersed in an ice-salt mixture.</p>
<p> ;</p>
<ul>
<li><strong>Apparatus:</strong></li>
</ul>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<ul>
<li><strong>Equation:</strong></li>
</ul>
<p>2Pb(NO<sub>3</sub>)<sub>2(s)</sub> 2PbO<sub>(s)</sub> + 4NO<sub>2(g)</sub> + O<sub>2(g)</sub></p>
<ul>
<li><strong>Observations:</strong></li>
</ul>
<p>&#8211; The heated <strong>white</strong> lead (II) nitrate crystals decompose and <strong>decrepitates</strong> (cracking sound) to yield <strong>red</strong> lead (II) oxide; which turns <strong>yellow</strong> on cooling.</p>
<p>&#8211; A <strong>colourless gas</strong>, oxygen is liberated, followed immediately by <strong>brown fumes</strong> of nitrogen (IV) oxide.</p>
<p>&#8211; Nitrogen (IV) oxide is condensed as a <strong>yellow liquid; dinitrogen tetroxide</strong> (N<sub>2</sub>O<sub>4</sub>); and is collected in the U-tube.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; At room temperature, nitrogen (IV) oxide consists of <strong>nitrogen (IV) oxide</strong> and <strong>dinitrogen tetroxide</strong> in equilibrium with each other.</p>
<p> ;</p>
<p><strong>Equation:<br />
</strong>2NO<sub>2(g)</sub> N<sub>2</sub>O<sub>4(g)</sub></p>
<p><strong><em>(Nitrogen (IV) oxide) (Dinitrogen tetroxide)</em></strong></p>
<p> ;</p>
<p>&#8211; The oxygen being liberated does not condense because it ahs a low boiling point of -183oC.</p>
<p> ;</p>
<p><strong>Properties of nitrogen (IV) oxide.</strong></p>
<ol>
<li><strong>Red-brown</strong> gas with a pungent chocking smell</li>
<li>It is extremely poisonous.</li>
<li>It is <strong>acidic</strong>, hence turns moist litmus paper red.</li>
<li>When reacted with water, the brown fumes dissolve showing that it is readily <strong>soluble in water</strong>.</li>
</ol>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2NO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> HNO<sub>3(aq)</sub> + HNO<sub>2(aq)</sub></p>
<p><strong><em>(Nitric (V) acid) (Nitrous (III) acid)When liquid nitrogen </em></strong></p>
<p> ;</p>
<p>&#8211; Like carbonic (IV) acid, nitrous (III) acid could not be isolated. It is easily oxidized to nitric (V) acid.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2NHO<sub>2(aq)</sub> + O<sub>2(g)</sub> 2NHO<sub>3(aq)</sub></p>
<p><strong><em>(Nitric (III) acid) (Nitrous (V) acid)</em></strong></p>
<p> ;</p>
<ol start="5">
<li><strong> Reaction with magnesium.</strong></li>
</ol>
<p>&#8211; Nitrogen (IV) oxide does not support combustion.</p>
<p>&#8211; However burning magnesium continues to burn in it.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; The high <strong>heat of combustion</strong> of burning magnesium decomposes the nitrogen (IV) oxide to nitrogen and oxygen; the oxygen then supports the burning of the magnesium.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>4MgO<sub>(s)</sub> + 2NO<sub>2(g)</sub> 4MgO<sub>(s)</sub> + 2N<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Generally nitrogen (IV) oxide oxidizes hot metals and non-metals to oxides and itself reduced to nitrogen gas.</p>
<p><strong>Examples:</strong></p>
<p><strong>(i). Copper:</strong></p>
<p>4Cu<sub>(s)</sub> + 2NO<sub>2(g)</sub> 4CuO<sub>(s)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>(ii). Phosphorus:</strong></p>
<p>8P<sub>(s)</sub> + 10NO<sub>2(g)</sub> 4P<sub>2</sub>O<sub>5(s)</sub> + 5N<sub>2(g)</sub></p>
<p><strong>(iii). Sulphur:</strong></p>
<p>2S<sub>(s)</sub> + 2NO<sub>2(g)</sub> 2SO<sub>2(g)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; NO<sub>2</sub> reacts with burning substances because the heat decomposes it to NO<sub>2</sub> and O<sub>2</sub>.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2NO<sub>2(g)</sub> <strong><em><sup>Heat</sup> </em></strong> 2NO<sub>(g)</sub> + O<sub>2(g)</sub></p>
<p> ;</p>
<p>&#8211; This is the oxidizing property of nitrogen (IV) oxide.</p>
<p>&#8211; The resultant oxygen supports the burning.</p>
<p> ;</p>
<ol start="6">
<li><strong> Effects of heat:</strong></li>
</ol>
<p>&#8211; On heating, nitrogen (IV) oxide dissociates to nitrogen (II) oxide and oxygen and will support a burning splint.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2NO<sub>2(g)</sub> <strong><em><sup>Heat</sup></em></strong> 2NO<sub>(g)</sub> + O<sub>2(g)</sub></p>
<p> ;</p>
<ol start="7">
<li>&#8211; When liquid nitrogen (IV) oxide or dinitrogen tetroxide is warmed, it produces a <strong>pale brown vapour</strong>.</li>
</ol>
<p>&#8211; This is due to the reversible set of reactions:</p>
<p><strong><em>Heat Heat</em></strong></p>
<p>N<sub>2</sub>O<sub>4(l)</sub> 2NO<sub>2(g)</sub> 2NO<sub>(g)</sub> + O<sub>2(g)</sub></p>
<p><strong><em>(Dinitrogen tetroxide) Cool (Nitrogen (IV) oxide) Cool (Nitrogen (II) oxide) (Oxygen)</em></strong></p>
<p><strong><em>Pale yellow Brown </em></strong></p>
<p><strong><em> Colourless</em></strong></p>
<p>&#8211; Percentage of each in the equilibrium depends on temperature.</p>
<p>&#8211; At low temperatures, percentage of N<sub>2</sub>O<sub>4</sub> is high and the mixture is pale yellow in colour.</p>
<p>&#8211; Percentage of nitrogen (IV) oxide increases with increase in temperature and the colour darkens till at 150<sup>o</sup>C when the gas is entirely NO<sub>2</sub> and is almost black.</p>
<p>&#8211; Still at higher temperatures, nitrogen (IV) oxide dissociates into colourless gas (NO and O<sub>2</sub>).</p>
<p> ;</p>
<ol start="8">
<li><strong> Reaction with alkalis.</strong></li>
</ol>
<p>&#8211; A solution of aqueous sodium hydroxide is added to a gas jar of nitrogen (IV) oxide and shaken.</p>
<p> ;</p>
<p><strong>Observation:</strong></p>
<p>&#8211; The brown fumes disappear.</p>
<p><strong> </strong></p>
<p><strong>Explanation:</strong></p>
<p>&#8211; Formation of sodium nitrate and sodium nitrite.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2NaOH<sub>(aq)</sub> + 2NO<sub>2(g) </sub> 2NaNO<sub>3(g)</sub> + NaNO<sub>2(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>2OH<sup>&#8211;</sup><sub>(aq)</sub> + 2NO<sub>2(g)</sub> NO<sub>3</sub><sup>&#8211;</sup><sub>(aq)</sub> + NO<sub>2</sub><sup>&#8211;</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Conclusion:</strong></p>
<p>Nitrogen (IV) oxide is an acidic gas because it can react with an alkali.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Uses of nitrogen (IV) oxide.</strong></p>
<ol>
<li>Mainly used in the manufacture of nitric (V) acid.</li>
</ol>
<p><strong> </strong></p>
<p><strong>Summary on comparison between oxides of nitrogen.</strong></p>
<p><strong> </strong></p>
<table>
<tbody>
<tr>
<td width="165"> ;</td>
<td width="225"><strong>Nitrogen (I) oxide</strong></td>
<td width="240"><strong>Nitrogen (II) oxide</strong></td>
<td width="207"><strong>Nitrogen (IV) oxide</strong></td>
</tr>
<tr>
<td width="165">Colour</td>
<td width="225">&#8211; Colourless gas</p>
<p>&#8211; Sweet sickly smell</td>
<td width="240">&#8211; Colourless; turns brown in air;</p>
<p>&#8211; Odourless</td>
<td width="207">&#8211; Red brown gas;</p>
<p>&#8211; Choking pungent smell;</td>
</tr>
<tr>
<td width="165">2. Solubility</td>
<td width="225">&#8211; Fairly soluble in cold water; but less soluble in hot water;</td>
<td width="240">&#8211; Almost insoluble in water</td>
<td width="207">&#8211; Readily soluble in water to form nitric (V) acid and nitrous (III) acid;</td>
</tr>
<tr>
<td width="165">3. Action on litmus</td>
<td width="225">&#8211; Neutral to litmus</td>
<td width="240">&#8211; Neutral to litmus</td>
<td width="207">&#8211; Turns moist blue litmus paper red; i.e. acidic.</td>
</tr>
<tr>
<td width="165">4. Combustion</td>
<td width="225">&#8211; Supports combustion; relights a glowing splint;</td>
<td width="240">&#8211; Does not support combustion;</td>
<td width="207">&#8211; Does not support combustion.</td>
</tr>
<tr>
<td width="165">5. Density</td>
<td width="225">&#8211; Denser than air</td>
<td width="240">&#8211; Slightly denser than air</td>
<td width="207">&#8211; Denser than air;</td>
</tr>
<tr>
<td width="165">6. Raw materials and conditions</td>
<td width="225">&#8211; Ammonium nitrate and heat;</td>
<td width="240">&#8211; Copper and 50% nitric acid;</td>
<td width="207">&#8211; Copper metal and concentrated nitric acid;</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>Action of heat on nitrates.</strong></p>
<p>&#8211; All nitrates except ammonium nitrate decompose on heating tom produce oxygen gas as one of the products.</p>
<p>&#8211; Nitrates can be categorized into 4 categories based on the products formed when they are heated.</p>
<p><strong>&#8211; </strong>The ease with which nitrates decompose increases down the electrochemical series of metals.</p>
<p> ;</p>
<ol>
<li>Nitrates of metals higher in the electrochemical series like sodium and potassium decompose on heating to give the corresponding metal nitrite and oxygen.</li>
</ol>
<p><strong> </strong></p>
<p><strong>Examples:</strong></p>
<p>2NaNO<sub>3(s)</sub> <sup>Heat</sup> 2NaNO<sub>2(s)</sub> + O<sub>2(g)</sub></p>
<p><strong> </strong></p>
<p>2KNO<sub>3(s)</sub> <sup>Heat</sup> 2KNO<sub>2(s)</sub> + O<sub>2(g)</sub></p>
<p><strong> </strong></p>
<ol start="2">
<li>Nitrates of most other metals (heavy metals) that are average in the electrochemical series decompose on heating to give the metals oxide; nitrogen (IV) oxide and oxygen gas.</li>
</ol>
<p> ;</p>
<p><strong>Example: action of heat on lead (II) nitrate.</strong></p>
<p><strong>(i). Apparatus:</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Solid white lead (II) nitrate crystals are strongly heated in a boiling (ignition) tube.</p>
<p><strong>&#8211; </strong>Products are passed into a U- tube immerse in ice.</p>
<p>&#8211; Excess gases are channeled out to a fume chamber.</p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; The white crystalline solid decrepitates.</p>
<p>&#8211; A colourless gas (<strong>oxygen</strong>) is liberated and immediately followed by a red brown fumes/ gas (<strong>nitrogen (IV) oxide</strong>).</p>
<p>&#8211; A pale yellow liquid (<strong>dinitrogen tetroxide</strong>) condenses in the U-tube in the ice cubes.</p>
<p>&#8211; This is due to condensation of nitrogen (IV) oxide.</p>
<p>&#8211; A residue which is <strong>red</strong> when hot and <strong>yellow</strong> on cooling remains in the boiling (ignition) tube</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2Pb(NO<sub>3</sub>)<sub>2(s)</sub> <sup>Heat</sup> 2PbO<sub>(s)</sub> + 4NO<sub>2(g)</sub> + O<sub>2(g)</sub></p>
<p><em>(White crystalline solid) (Red-hot Brown Fumes Colourless gas<br />
yellow-cold)</em></p>
<p><em> </em></p>
<p><strong>Further examples:</strong></p>
<p> ;</p>
<p>2Ca(NO<sub>3</sub>)<sub>2(s)</sub> <sup>Heat</sup> 2CaO<sub>(s)</sub> + 4NO<sub>2(g) </sub> + O<sub>2(g)</sub></p>
<p><em>(White solid) (White solid) Brown Fumes Colourless gas</p>
<p></em></p>
<p>2Mg(NO<sub>3</sub>)<sub>2(s)</sub> <sup>Heat</sup> 2MgO<sub>(s)</sub> + 4NO<sub>2(g)</sub> + O<sub>2(g)</sub></p>
<p><em>(White solid) (White solid) Brown Fumes Colourless gas<br />
</em></p>
<p>2Zn(NO<sub>3</sub>)<sub>2(s)</sub> <sup>Heat</sup> 2ZnO<sub>(s)</sub> + 4NO<sub>2(g)</sub> + O<sub>2(g)</sub></p>
<p><em>(White solid) (Yellow-hot Brown Fumes Colourless gas<br />
White-cold)</em></p>
<p><em> </em></p>
<p>2Cu(NO<sub>3</sub>)<sub>2(s)</sub> <sup>Heat</sup> 2CuO<sub>(s)</sub> + 4NO<sub>2(g)</sub> + O<sub>2(g)</sub></p>
<p><em>(Blue solid) (Black solid) Brown Fumes Colourless gas</p>
<p></em></p>
<p><strong>Note:</strong></p>
<p>&#8211; Some nitrates are <strong>hydrated</strong> and when heated first give out their water of crystallization; and then proceed to as usual on further heating.</p>
<p><strong> </strong></p>
<p><strong>Examples:</strong></p>
<p><strong> </strong></p>
<p>Ca(NO<sub>3</sub>)<sub>2</sub>.4H<sub>2</sub>O<sub>(s)</sub> <sup>Heat</sup> Ca(NO<sub>3</sub>)<sub>2(s)</sub> + 4H<sub>2</sub>O<sub>(g) </sub></p>
<p><em>(White solid) (White solid) Colourless gas</p>
<p></em></p>
<p>On further heating;</p>
<p><strong> </strong></p>
<p>2Ca(NO<sub>3</sub>)<sub>2(s)</sub> <sup>Heat</sup> 2CaO<sub>(s)</sub> + 4NO<sub>2(g) </sub> + O<sub>2(g)</sub></p>
<p><em>(White solid) (White solid) Brown Fumes Colourless gas</p>
<p></em></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<ol start="3">
<li>Nitrates of metals lower in the reactivity series e.g. <strong>mercury</strong> and <strong>silver</strong> decompose on heating to give the metal, nitrogen (IV) oxide and oxygen.</li>
</ol>
<p> ;</p>
<p><strong>Example:</strong></p>
<p><strong> </strong></p>
<p>Hg(NO<sub>3</sub>)<sub>2(s)</sub> <sup>Heat</sup> Hg<sub>(s)</sub> + 2NO<sub>2(g) </sub> + O<sub>2(g)</sub></p>
<p><em>(White solid) Brown Fumes Colourless gas</p>
<p></em></p>
<p>2AgNO<sub>3(s)</sub> <sup>Heat</sup> 2Ag<sub>(s)</sub> + 2NO<sub>2(g) </sub> + O<sub>2(g)</sub></p>
<p><em>(White solid) Brown Fumes Colourless gas</p>
<p></em></p>
<ol start="4">
<li>Ammonium nitrate decomposes to nitrogen (I) oxide and water vapour.</li>
</ol>
<p> ;</p>
<p><strong>Example:</strong></p>
<p>NH<sub>4</sub>NO<sub>3(s)</sub> <sup>Heat</sup> N<sub>2</sub>O<sub>(g) </sub> + O<sub>2(g)</sub></p>
<p><em> Colourless gas Colourless gas<br />
</em><strong>Note:</strong></p>
<p>This reaction is potentially dangerous as ammonium nitrate <strong>explodes</strong> on strong heating.</p>
<p> ;</p>
<p><strong>Ammonia.</strong></p>
<p>&#8211; Is a compound of nitrogen and hydrogen and is the most important hydride of nitrogen.</p>
<p>&#8211; It is formed when any <strong>ammonium salt</strong> is heated with an <strong>alkali</strong> whether in solid or solution form.</p>
<p>&#8211; It is a <strong>colourless</strong> gas with a pungent smell of <strong>urine</strong>.</p>
<p>&#8211; It is <strong>alkaline</strong> and turns moist red litmus paper to blue when introduced to it.</p>
<p> ;</p>
<p><strong>Laboratory preparation of ammonia.</strong></p>
<p><strong>(i). Reagents.</strong></p>
<p>Base + ammonium salt NH<sub>3(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>(ii). Apparatus.</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(iii). Procedure.</strong></p>
<p>&#8211; Ammonium chloride (NH<sub>4</sub>Cl)/ sal-ammoniac is mixed with a little dry slaked lime i.e. Ca(OH)<sub>2</sub> and the mixture thoroughly ground in a mortar.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; To increase surface area for the reactions.</p>
<p> ;</p>
<p>&#8211; The mixture is then heated in a round-bottomed flask.</p>
<p><strong>Note:</strong></p>
<p>&#8211; A round-bottomed flask ensures <strong>uniform distribution</strong> of heat while heating the reagents.</p>
<p>&#8211; The flask should not be <strong>thin-walled</strong>.</p>
<p><strong>Reason:</strong></p>
<p>The pressure of ammonia gas liberated during heating may easily <strong>crack or break</strong> it.</p>
<p> ;</p>
<p>&#8211; The flask is positioned <strong>slanting downwards</strong>.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; So that as water condenses from the reaction, it does not run back to the hot parts of the flask and crack it.</p>
<p>&#8211; The mixture on heating produces ammonia, calcium chloride and water.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Ca(OH)<sub>2(s)</sub> + NH<sub>4</sub>Cl<sub>(s)</sub> CaCl<sub>2(aq)</sub> + 2NH<sub>3(g)</sub> + 2H<sub>2</sub>O<sub>(g)</sub></p>
<p><strong><em>(Slaked lime)</em></strong></p>
<p> ;</p>
<p><strong>(iv). Drying:</strong></p>
<p>&#8211; Ammonia is dried by passing it through a tower or U-tube filled with quicklime (calcium oxide) or pellets of caustic potash but not caustic soda which is <strong>deliquescent.</strong></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>Ammonia cannot be dried with the usual drying agents; concentrated sulphuric acid and calcium chloride as it reacts with them.</p>
<ul>
<li><strong>With concentrated sulphuric acid.</strong></li>
</ul>
<p>2NH<sub>3(g)</sub> + H<sub>2</sub>SO<sub>4(l)</sub> (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(aq)</sub></p>
<p> ;</p>
<ul>
<li><strong>With fused calcium chloride:</strong></li>
</ul>
<p>CaCl<sub>2(aq)</sub> + 4NH<sub>3(g)</sub> CaCl<sub>2</sub>.4NH<sub>3(s)</sub></p>
<p> ;</p>
<p>&#8211; i.e. ammonia reacts forming <strong>complex ammonium salt.</strong></p>
<p> ;</p>
<p><strong>(v). Collection:</strong></p>
<p>&#8211; Dry ammonia gas is collected by <strong>upward delivery</strong>.</p>
<p><strong>Reasons:</strong></p>
<p>&#8211; It is <strong>lighter</strong> than air.</p>
<p>&#8211; It is <strong>soluble</strong> in water.</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Other methods of preparing ammonia.</strong></p>
<p><strong> </strong></p>
<p>(b). Ammonia from caustic soda (sodium hydroxide) or caustic potash (potassium hydroxide)</p>
<p>Note:</p>
<p>&#8211; The slaked lime is replaced by either of the above solutions.</p>
<p>&#8211; Thus the solid reactant is ammonium chloride and the liquid reactant is potassium hydroxide.</p>
<p> ;</p>
<p>(i). Apparatus:</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; The flask is not slanted. It is vertical and heated on a tripod stand and wire gauze.</p>
<p>Reason:</p>
<p>&#8211; No need of slanting since water produced is in liquid form and not gaseous. Thus there is no possibility of condensation of water on hotter parts.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p><strong>(i). With caustic soda:</strong></p>
<p>NaOH<sub>(aq)</sub> + NH<sub>4</sub>Cl<sub>(s)</sub> NaCl<sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>Na<sup>+</sup><sub>(aq)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub> + NH<sub>4</sub>Cl<sub>(s)</sub> Na<sup>+</sup><sub>(aq)</sub> + Cl<sup>&#8211;</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Hence;</strong> NH<sub>4</sub>Cl<sub>(s)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub> Cl<sup>&#8211;</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>(ii). With caustic potash:</strong></p>
<p>KOH<sub>(aq)</sub> + NH<sub>4</sub>Cl<sub>(s)</sub> KCl<sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>K<sup>+</sup><sub>(aq)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub> + NH<sub>4</sub>Cl<sub>(s)</sub> K<sup>+</sup><sub>(aq)</sub> + Cl<sup>&#8211;</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Hence;</strong> NH<sub>4</sub>Cl<sub>(s)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub> Cl<sup>&#8211;</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>Ammonium sulphate could be used in place of ammonium chloride in either case.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p> ;</p>
<p><strong>(i). With caustic soda:</strong></p>
<p>2NaOH<sub>(aq)</sub> + (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> Na<sub>2</sub>SO<sub>4(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + 2NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>2Na<sup>+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> + (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> 2Na<sup>+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Hence;</strong> (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + 2NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>(ii). With caustic potash:</strong></p>
<p>2KOH<sub>(aq)</sub> + (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> K<sub>2</sub>SO<sub>4(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + 2NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>2K<sup>+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> + (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> 2K<sup>+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Hence;</strong> (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + 2NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>(iii). With calcium hydroxide:</strong></p>
<p>Ca(OH)<sub>2(aq)</sub> + (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> CaSO<sub>4(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + 2NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>Ca<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> + (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> Ca<sup>2+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Hence;</strong> (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + 2NH<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>Reaction with calcium hydroxide however stops prematurely, almost as soon as the reaction starts.</p>
<p><strong>Reason;</strong></p>
<p>&#8211; Formation of insoluble calcium sulphate which coats the ammonium sulphate preventing further reaction.</p>
<p> ;</p>
<p><strong>Preparation of ammonium solution.</strong></p>
<p><strong>(i). Apparatus.</strong></p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; The apparatus is altered as above.</p>
<p>&#8211; The drying tower is removed and the gas produced is directly passed into water by an inverted funnel.</p>
<p> ;</p>
<p><strong>Reasons for the inverted broad funnel.</strong></p>
<p>&#8211; It increases the <strong>surface area</strong> for the <strong>dissolution</strong> of thereby preventing water from Â<strong>sucking back</strong>Â into the hot flask and hence prevents chances of an <strong>explosion.</strong></p>
<p> ;</p>
<p><strong>(iii). Equation.</strong></p>
<p>NH<sub>3(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> NH<sub>4</sub>OH<sub>(aq)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; The solution cannot be prepared by leading the gas directly to water by the delivery tube.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; Ammonia gas is <strong>very soluble</strong> in water and so water would rush up the delivery tube and into the hot flask causing it to crack.</p>
<p>&#8211; The rim of the inverted funnel is <strong>just below</strong> the water surface.</p>
<p> ;</p>
<p><strong>Tests for ammonia.</strong></p>
<ol>
<li>It is a colourless gas with a <strong>pungent smell.</strong></li>
<li>It is the only common gas that is <strong>alkaline</strong> as it turns moist red litmus paper blue.</li>
<li>When ammonia is brought into contact with hydrogen chloride gas, <strong>dense white fumes</strong> of ammonium chloride are formed.</li>
</ol>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>NH<sub>3(g)</sub> + HCl<sub>(g) </sub> NH<sub>4</sub>Cl<sub>(s)</sub></p>
<p> ;</p>
<p><strong>Fountain experiment.</strong></p>
<p><strong>(i). Diagram:</p>
<p></strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Dry ammonia is collected in a round-bottomed flask and set up as above.</p>
<p>&#8211; The clip is open and solution let to rise up the tube.</p>
<p>&#8211; The clip is closed when the solution reaches the top of the tube after which it is again opened fro a while.</p>
<p> ;</p>
<p><strong>(iii). Observations and explanations.</strong></p>
<p>&#8211; When a drop of water gets to the jet, it dissolves so much of the ammonia gas that a <strong>partial vacuum</strong> is created inside the flask.</p>
<p>&#8211; As the ammonia in the flask dissolves, the pressure in the flask is <strong>greatly reduced</strong>.</p>
<p>&#8211; The atmospheric pressure on the water surface in the beaker forces water into the flask vigorously.</p>
<p>&#8211; The drawn-out jet of the tube causes a <strong>fountain </strong>to be produced.</p>
<p>&#8211; The fountain appears <strong>blue </strong>due to the <strong>alkaline </strong>nature of ammonia.</p>
<p> ;</p>
<p><strong>(iv). Caution:</strong></p>
<p>&#8211; Ammonia is highly soluble in water forming an alkaline solution of ammonium hydroxide.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>1 volume of water dissolves about 750 volumes of ammonia at room temperature.</p>
<p> ;</p>
<p><strong>Properties and reactions of ammonia.</strong></p>
<ol>
<li><strong>Smell:</strong> has a characteristic pungent smell.</li>
<li><strong>Solubility:</strong> it is highly soluble in water. The dissolved ammonia molecule reacts partially with water to form ammonium ions (NH<sub>4</sub><sup>+</sup>) and hydroxyl ions (OH<sup>&#8211;</sup>)</li>
</ol>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>NH<sub>3(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> NH4<sup>+</sup><sub>(aq)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; Formation of hydroxyl ions means that the aqueous solution of ammonia is (weakly) alkaline and turns universal indicator purple.</p>
<p> ;</p>
<ol start="3">
<li><strong> Reaction with acids.</strong></li>
</ol>
<p>&#8211; Sulphuric acid and concentrated ammonia solution are put in a dish and heated slowly.</p>
<p>&#8211; The mixture is evaporated to dryness.</p>
<p> ;</p>
<p><strong>Observations:</strong></p>
<p>&#8211; A white solid is formed.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2NH<sub>4</sub>OH<sub>(aq)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>2NH<sub>4</sub><sup>+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> + 2H<sup>+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> 2NH<sub>4</sub><sup>+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + 2H<sup>+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub>.</p>
<p> ;</p>
<p>Then;</p>
<p>2H<sup>+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> 2H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>&#8211; To some of the resultant white solid, a little NaOH<sub>(aq)</sub> was added and the mixture warmed.</p>
<p>&#8211; The gas evolved was tested fro ammonia.</p>
<p> ;</p>
<p><strong>Observation:</strong></p>
<p>&#8211; The resultant gas tested positive for ammonia.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>(NH<sub>4</sub>)<sub>2</sub>SO<sub>4(s)</sub> + 2NaOH<sub>(aq)</sub> Na<sub>2</sub>SO<sub>4(aq)</sub> + 2NH<sub>3(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub>.</p>
<p> ;</p>
<p> ;</p>
<p><strong>Explanations:</strong></p>
<p>&#8211; Evolution of ammonia shows that the white solid formed is an <strong>ammonium salt.</strong></p>
<p>&#8211; The ammonia reacts with acids to from ammonium salt and water only.</p>
<p> ;</p>
<p><strong>Further examples:<br />
</strong>HCl<sub>(aq) </sub>+ NH<sub>4</sub>OH<sub>(aq)</sub> NH<sub>4</sub>Cl<sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>HNO<sub>3(aq)</sub> + NH<sub>4</sub>OH<sub>(aq)</sub> NH<sub>4</sub>NO<sub>3(aq) </sub>+ H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Ionic equation:</strong></p>
<p>NH<sub>3(g)</sub> + H<sup>+</sup><sub>(aq)</sub> NH<sub>4</sub><sup>+</sup><sub>(aq)</sub></p>
<p> ;</p>
<ol start="4">
<li><strong> Reaction of ammonia with oxygen.</strong></li>
</ol>
<p>&#8211; Ammonia <strong>extinguishes</strong> a lighted taper because it dos not support burning.</p>
<p>&#8211; It is <strong>non-combustible</strong>.</p>
<p>&#8211; However it burns in air enriched with oxygen with a <strong>green-yellow flame</strong>.</p>
<p> ;</p>
<p><strong>Experiment: Burning ammonia in oxygen.</strong></p>
<p><strong>(i). Apparatus.</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Dry oxygen is passed in the U-tube for a while to drive out air.</p>
<p>&#8211; Dry ammonia gas is then passed into the tube.</p>
<p>&#8211; A lighted splint is then passed into the tube.</p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; A colourless gas is liberated.</p>
<p>&#8211; Droplets of a colourless liquid collect on cooler parts of the tube.</p>
<p> ;</p>
<p><strong>(iv). Explanations:</strong></p>
<p>&#8211; The conditions for the reactions are:</p>
<ul>
<li>Dry ammonia and oxygen gas i.e. the gases must be <strong>dry</strong>.</li>
<li>All air must be driven out of the tube.</li>
</ul>
<p>&#8211; Ammonia burns continuously in oxygen (air enriched with oxygen) forming nitrogen and water vapour i.e. ammonia is oxidized as hydrogen is removed from it leaving nitrogen.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>4NH<sub>3(g)</sub> + 3O<sub>2(g)</sub> 2N<sub>2(g)</sub> + 6H<sub>2</sub>O<sub>(g)</sub></p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Sample question:</strong></p>
<p><em>Suggest the role of glass wool in the tube.</em></p>
<p> ;</p>
<p><strong>Solution:</strong></p>
<p>&#8211; To slow down the escape of oxygen in the combustion tube, thus providing more time for combustion of ammonia.</p>
<p> ;</p>
<ol start="5">
<li><strong> Ammonia as a reducing agent.</strong></li>
</ol>
<p>&#8211; It reduces oxides of metals below iron in the reactivity series.</p>
<p> ;</p>
<p>Experiment: reaction between ammonia and copper (II) oxide.</p>
<p>(i). Apparatus.</p>
<table>
<tbody>
<tr>
<td width="76">
<table width="100%">
<tbody>
<tr>
<td>Ice cubes</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Copper (II) oxide is heated strongly and dry ammonia is passed over it.</p>
<p>&#8211; The products are then passed through a U-tube immersed in cold water (ice cubes).</p>
<p> ;</p>
<p><strong>(iii). Observations.</strong></p>
<p>&#8211; The copper (II) oxide <strong>glows</strong> as the reaction is <strong>exothermic</strong>.</p>
<p>&#8211; A <strong>colourless liquid</strong> collects in the U-tube.</p>
<p>&#8211; A <strong>colourless gas</strong> is collected over water.</p>
<p>&#8211; The <strong>black</strong> copper (II) oxide changes to <strong>brown</strong> copper metal.</p>
<p> ;</p>
<p><strong>(iv). Explanations.</strong></p>
<p>&#8211; Ammonia gas <strong>reduces</strong> copper (II) oxide to copper and is itself <strong>oxidized</strong> to nitrogen and water.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>3CuO<sub>(s)</sub> + 2NH<sub>3(g)</sub> 3Cu<sub>(s)</sub> + 3H<sub>2</sub>O<sub>(l)</sub> + N<sub>2(g)</sub></p>
<p><strong><em>Black red-brown (colourless)</em></strong></p>
<p> ;</p>
<p>&#8211; The water produced condenses in the U-tube immersed in cold (ice) water.</p>
<p>&#8211; The resultant nitrogen is collected by downward displacement of water.</p>
<p>&#8211; The nitrogen gas collected is ascertained indirectly as follows:</p>
<ul>
<li>A lighted splint is extinguished and the gas does not burn; thus it is not oxygen, hydrogen, or carbon (II) oxide.</li>
<li>It has neither smell nor colour; it is not ammonia, chlorine, sulphur (IV) oxide or nitrogen (IV) oxide.</li>
<li>It is not carbon (II) oxide because it does not turn lime water into a white precipitate.</li>
</ul>
<p> ;</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; This experiment proves that ammonia contains nitrogen.</p>
<p> ;</p>
<ol start="6">
<li><strong> Reaction with chlorine.</strong></li>
</ol>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; Ammonia gas is passed into a bell jar containing chlorine.</p>
<p> ;</p>
<p><strong>(ii). Apparatus:</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; The ammonia catches fire and burns for a while at the end of the tube.</p>
<p>&#8211; The flame then goes out and the jar then gets filled with dense white fumes of ammonium chloride.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>2NH<sub>3(g)</sub> + 3Cl<sub>2(g)</sub> 6HCl<sub>(g)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<p>Then;</p>
<p>6HCl<sub>(g)</sub> + 6NH<sub>3(g)</sub> 6NH<sub>4</sub>Cl<sub>(s)</sub></p>
<p> ;</p>
<p><strong>Overall equation:</strong></p>
<p>8NH<sub>3(g) </sub>+ 3Cl<sub>2(g) </sub> 6NH<sub>4</sub>Cl<sub>(s)</sub> + N<sub>2(g)</sub></p>
<p> ;</p>
<ol start="7">
<li><strong> Ammonia solution as an alkali.</strong></li>
</ol>
<p>&#8211; Solution of ammonia in water contains hydroxyl ions.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>NH<sub>3(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> NH<sub>4</sub><sup>+</sup><sub>(aq)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; Thus it has many properties of a <strong>typical alkali.</strong></p>
<p>&#8211; Ammonia salts are similar to metallic salts.</p>
<p>&#8211; The group (NH<sub>4</sub><sup>+</sup>) precipitates in the reaction as a whole without splitting in any way.</p>
<p>&#8211; It exhibits unit valency in its compounds and therefore called a <strong>basic radical.</strong></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; It cannot exist freely as ammonia gas (NH<sub>3</sub>) which is a compound.</p>
<p>&#8211; Like other alkalis, ammonia solution precipitates insoluble metallic hydroxides by double decomposition when mixed with solution of salts of the metals.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<ol start="8">
<li><strong> Reaction with air in the presence of platinum wire.</strong></li>
</ol>
<p><strong>(i). Apparatus:</strong></p>
<p><strong> </strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Concentrated ammonia solution is put in a conical flask.</p>
<p>&#8211; The platinum (or even copper) wire is heated until white-hot.</p>
<p>&#8211; Oxygen gas or air is then passed through the ammonia solution.</p>
<p>&#8211; The red-hot platinum (copper) wire is then put into the flask containing the concentrated ammonia.</p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; The hot platinum wire <strong>glows</strong>.</p>
<p>&#8211; Red-brown fumes are evolved.</p>
<p> ;</p>
<p><strong>(iv). Explanations:</strong></p>
<p>&#8211; The hot platinum coil glows when it comes into contact with the ammonia fumes, which come from the concentrated ammonia solution.</p>
<p>&#8211; Reaction between ammonia and oxygen takes place on the <strong>surface of the platinum</strong> wire that acts a s a <strong>catalyst.</strong></p>
<p>&#8211; A lot of <strong>heat</strong> is produced in the reaction that enables the platinum coil to continue glowing.</p>
<p>&#8211; Ammonia is oxidized to <strong>nitrogen (IV) oxide</strong>.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>4NH<sub>3(g)</sub> + 5O<sub>2(g) </sub><strong><sup>Platinum catalyst</sup> </strong>4NO<sub>(g)</sub> + 6H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>&#8211; Red-brown fumes of nitrogen (IV) oxide are produced due to further <strong>oxidation</strong> of the nitrogen (II) oxide to from nitrogen (IV) oxide.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2NO<sub>(g)</sub> + O<sub>2(g)</sub> 2NO<sub>2(g)</sub></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<ol start="9">
<li><strong> Action of aqueous ammonia on solution of metallic salts</strong></li>
</ol>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; To about 2cm<sup>3</sup> of solutions containing ions of calcium, magnesium, aluminium, zinc, iron, lead, copper etc in separate test tubes; aqueous ammonia is added dropwise till in excess.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p>The various metal ions reacted as summarized in the table below.</p>
<p> ;</p>
<table>
<tbody>
<tr>
<td rowspan="2" width="195"><strong>Metal ions in solution</strong></td>
<td colspan="2" width="615"><strong>Observations on addition of ammonia</strong></td>
</tr>
<tr>
<td width="308"><strong>Few drops of ammonia</strong></td>
<td width="308"><strong>Excess drops of ammonia</strong></td>
</tr>
<tr>
<td width="195">Ca<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">White precipitate persists;</td>
</tr>
<tr>
<td width="195">Mg<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate persists;</td>
</tr>
<tr>
<td width="195">Al<sup>3+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate persists;</td>
</tr>
<tr>
<td width="195">Zn<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate dissolves;</td>
</tr>
<tr>
<td width="195">Fe<sup>2+</sup></td>
<td width="308">Pale green precipitate</td>
<td width="308">Precipitate persists; slowly turns red-brown on exposure to air;</td>
</tr>
<tr>
<td width="195">Fe<sup>3+</sup></td>
<td width="308">Red-brown precipitate</td>
<td width="308">Precipitate persists;</td>
</tr>
<tr>
<td width="195">Pb<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate persists;</td>
</tr>
<tr>
<td width="195">Cu<sup>2+</sup></td>
<td width="308">Pale blue precipitate</td>
<td width="308">Precipitate dissolves forming a deep blue solution;</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>(iii). Explanations:</strong></p>
<p>&#8211; Most metal ions in solution react with ammonia solution to form insoluble metal hydroxides.</p>
<p>&#8211; In excess ammonia, some of the so formed hydroxides dissolve forming complex ions.</p>
<p> ;</p>
<p><strong>(iv). Equations:</strong></p>
<p><strong> </strong></p>
<ol>
<li><strong> Mg<sup>2+</sup><sub>(aq)</sub> from MgCl<sub>2</sub>;</strong></li>
</ol>
<p> ;</p>
<p>MgCl<sub>2(aq)</sub> + 2NH<sub>4</sub>OH<sub>(aq)</sub> Mg(OH)<sub>2(s)</sub> + 2NH<sub>4</sub>Cl<sub>(aq)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>Mg<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Mg(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt)</em></strong></p>
<p> ;</p>
<ol start="2">
<li><strong> Fe<sup>2+</sup> from Fe(NO<sub>3</sub>)<sub>2</sub>;</strong></li>
</ol>
<p> ;</p>
<p>Fe(NO<sub>3</sub>)<sub>2(aq)</sub> + 2NH<sub>4</sub>OH<sub>(aq)</sub> Fe(OH)<sub>2(s)</sub> + 2NH<sub>4</sub>NO<sub>3(aq)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>Fe<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Fe(OH)<sub>2(s)</sub></p>
<p><strong><em>(Pale green ppt)</em></strong></p>
<p> ;</p>
<ol start="3">
<li><strong> Fe<sup>3+</sup> from FeCl<sub>3</sub>;</strong></li>
</ol>
<p><strong> </strong></p>
<p><strong>Ionically:</strong></p>
<p>Fe<sup>3+</sup><sub>(aq)</sub> + 3OH<sup>&#8211;</sup><sub>(aq)</sub> Fe(OH)<sub>3(s)</sub></p>
<p><strong><em>(Red brown ppt)</em></strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>Zn<sup>2+</sup><sub>(aq) </sub>and Cu<sup>2+</sup><sub>(aq)</sub> dissolve in excess ammonia solution forming complex ions.</p>
<p> ;</p>
<ol start="4">
<li><strong> Zinc ions and ammonia solution.</strong></li>
</ol>
<p><strong> </strong></p>
<ul>
<li><strong>With little ammonia:</strong></li>
</ul>
<p>ZnCl<sub>2(aq)</sub> + 2NH<sub>4</sub>OH<sub>(aq)</sub> Zn(OH)<sub>2(s)</sub> + 2NH<sub>4</sub>Cl<sub>(aq)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>Zn<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Zn(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt.)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>In excess ammonia:</strong></li>
</ul>
<p>&#8211; The white precipitate of Zn(OH)<sub>2(s)</sub> dissolves in excess ammonia to form a colourless solution; proof that solution has Zn<sup>2+ </sup>ions;</p>
<p>&#8211; The colourless solution is a complex salt of tetra-amine zinc (II) ions.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Zn(OH)<sub>2(s)</sub> + 4NH<sub>3(aq)</sub> [Zn(NH<sub>3</sub>)<sub>4</sub>]<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub></p>
<p><strong><em>(White ppt.) (Colourless solution-tetra amine zinc (II) ions)</em></strong></p>
<p> ;</p>
<ol start="5">
<li><strong> Copper (II) ions.</strong></li>
</ol>
<p><strong> </strong></p>
<ul>
<li><strong>With little ammonia:</strong></li>
</ul>
<p>&#8211; A pale blue precipitate is formed.</p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>Cu<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Cu(OH)<sub>2(s)</sub></p>
<p><strong><em>(Pale blue ppt.)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>In excess ammonia:</strong></li>
</ul>
<p>&#8211; The pale blue precipitate of Cu(OH)<sub>2(s)</sub> dissolves in excess ammonia to form a deep blue solution; proof that solution has Cu<sup>2+ </sup>ions;</p>
<p>&#8211; The deep blue solution is a complex salt of tetra-amine copper (II) ions.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Cu(OH)<sub>2(s)</sub> + 4NH<sub>3(aq)</sub> [Cu(NH<sub>3</sub>)<sub>4</sub>]<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub></p>
<p><strong><em>(Pale blue ppt.) (Deep blue solution-tetra amine copper (II) ions)</em></strong></p>
<p> ;</p>
<p><strong>Uses of ammonia gas and its solution:</strong></p>
<ol>
<li>Ammonia gas is used in the manufacture of <strong>nitric acid</strong> and nylon.</li>
<li>Ammonia gas is important in the preparation of <strong>ammonium salts</strong> used as <strong>fertilizers</strong>.</li>
<li>It liquefies fairly easily (B.P is -33<sup>o</sup>C) and the liquid is used as a <strong>refrigerant</strong> in large cold storages and ice cream factories.</li>
<li>Liquid ammonia is injected directly into the soil as a high nitrogen content <strong>fertilizer</strong>.</li>
<li>Ammonia solution is used in <strong>laundry work</strong> as a <strong>water softener</strong> and a <strong>cleansing agent</strong> (stain remover)</li>
<li>Ammonia is used in the manufacture of sodium carbonate in the <strong>Solvay process</strong>.</li>
<li>Ammonia is used in Â<strong>smelling salts</strong>Â. It has a slightly stimulating effect on the action of the heart and so may prevent fainting</li>
</ol>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Qualitative analysis for cations using sodium hydroxide solution</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; To about 2cm<sup>3</sup> of solutions containing ions of calcium, magnesium, aluminium, zinc, iron, lead, copper etc in separate test tubes; aqueous sodium hydroxide is added dropwise till in excess.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p>The various metal ions reacted as summarized in the table below.</p>
<p> ;</p>
<table>
<tbody>
<tr>
<td rowspan="2" width="195"><strong>Metal ions in solution</strong></td>
<td colspan="2" width="615"><strong>Observations on addition of ammonia</strong></td>
</tr>
<tr>
<td width="308"><strong>Few drops of ammonia</strong></td>
<td width="308"><strong>Excess drops of ammonia</strong></td>
</tr>
<tr>
<td width="195">Ca<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">White precipitate persists</td>
</tr>
<tr>
<td width="195">Mg<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate persists;</td>
</tr>
<tr>
<td width="195">Al<sup>3+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate dissolves;</td>
</tr>
<tr>
<td width="195">Zn<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate dissolves;</td>
</tr>
<tr>
<td width="195">Fe<sup>2+</sup></td>
<td width="308">Pale green precipitate</td>
<td width="308">Precipitate persists; slowly turns red-brown on exposure to air;</td>
</tr>
<tr>
<td width="195">Fe<sup>3+</sup></td>
<td width="308">Red-brown precipitate</td>
<td width="308">Precipitate persists;</td>
</tr>
<tr>
<td width="195">Pb<sup>2+</sup></td>
<td width="308">White precipitate</td>
<td width="308">Precipitate dissolves;</td>
</tr>
<tr>
<td width="195">Cu<sup>2+</sup></td>
<td width="308">Pale blue precipitate</td>
<td width="308">Precipitate dissolves forming a deep blue solution;</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>(iii). Explanations:</strong></p>
<p>&#8211; Most metal ions in solution react with sodium hydroxide solution to form insoluble metal hydroxides.</p>
<p>&#8211; In excess sodium hydroxide, some of the so formed hydroxides (hydroxides of Zn, Al, Pb and Cu) dissolve forming complex ions.</p>
<p> ;</p>
<p><strong>(iv). Equations:</strong></p>
<p>Ca<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Ca(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt)</em></strong></p>
<p><strong> </strong></p>
<p>Mg<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Mg(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt)</em></strong></p>
<p> ;</p>
<p>Al<sup>3+</sup><sub>(aq)</sub> + 3OH<sup>&#8211;</sup><sub>(aq)</sub> Al(OH)<sub>3(s)</sub></p>
<p><strong><em> (White ppt)</em></strong></p>
<p> ;</p>
<p>Zn<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Zn(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt)</em></strong></p>
<p> ;</p>
<p>Pb<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Pb(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt)</em></strong></p>
<p> ;</p>
<p>Cu<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Cu(OH)<sub>2(s)</sub></p>
<p><strong><em> (Pale blue ppt)</em></strong></p>
<p> ;</p>
<p>Fe<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Fe(OH)<sub>2(s)</sub></p>
<p><strong><em>(Pale green ppt)</em></strong></p>
<p> ;</p>
<p>Fe<sup>3+</sup><sub>(aq)</sub> + 3OH<sup>&#8211;</sup><sub>(aq)</sub> Fe(OH)<sub>3(s)</sub></p>
<p><strong><em>(Red brown ppt)</em></strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>Hydroxides of Zn<sup>2+</sup><sub>(aq) </sub>; Pb<sup>2+</sup><sub>(aq) </sub>; and Al<sup>3+</sup><sub>(aq)</sub> dissolve in excess ammonia solution forming complex ions.</p>
<p> ;</p>
<ol>
<li><strong> Zinc ions and sodium hydroxide solution.</strong></li>
</ol>
<p><strong> </strong></p>
<ul>
<li><strong>With little sodium hydroxide:</strong></li>
</ul>
<p> ;</p>
<p>Zn<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Zn(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt.)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>In excess sodium hydroxide:</strong></li>
</ul>
<p>&#8211; The white precipitate of Zn(OH)<sub>2(s)</sub> dissolves in excess sodium hydroxide to form a colourless solution;</p>
<p>&#8211; The colourless solution is a complex salt of tetra-hydroxo zinc (II) ions (zincate ion).</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Zn(OH)<sub>2(s)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> [Zn(OH)<sub>4</sub>]<sup>2-</sup><sub>(aq)</sub></p>
<p><strong><em>(White ppt.) (Colourless solution-tetra hydroxo- zinc (II) ion/ zincate ion)</em></strong></p>
<p> ;</p>
<ol start="2">
<li><strong> Aluminium ions and sodium hydroxide solution.</strong></li>
</ol>
<p><strong> </strong></p>
<ul>
<li><strong>With little sodium hydroxide:</strong></li>
</ul>
<p> ;</p>
<p>Al<sup>3+</sup><sub>(aq)</sub> + 3OH<sup>&#8211;</sup><sub>(aq)</sub> Al(OH)<sub>3(s)</sub></p>
<p><strong><em> (White ppt.)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>In excess sodium hydroxide:</strong></li>
</ul>
<p>&#8211; The white precipitate of Al(OH)<sub>3(s)</sub> dissolves in excess sodium hydroxide to form a colourless solution;</p>
<p>&#8211; The colourless solution is a complex salt of tetra-hydroxo aluminium (III) ions (aluminate ion).</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Al(OH)<sub>3(s)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub> [Al(OH)<sub>4</sub>]<sup>&#8211;</sup><sub>(aq)</sub></p>
<p><strong><em>(White ppt.) (Colourless solution-tetra hydroxo- aluminium (III) ion/aluminate ion</em></strong></p>
<p> ;</p>
<ol start="3">
<li><strong> Lead (II) ions and sodium hydroxide solution.</strong></li>
</ol>
<p><strong> </strong></p>
<ul>
<li><strong>With little sodium hydroxide:</strong></li>
</ul>
<p> ;</p>
<p>Pb<sup>2+</sup><sub>(aq)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> Pb(OH)<sub>2(s)</sub></p>
<p><strong><em> (White ppt.)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>In excess sodium hydroxide:</strong></li>
</ul>
<p>&#8211; The white precipitate of Pb(OH)<sub>2(s)</sub> dissolves in excess sodium hydroxide to form a colourless solution;</p>
<p>&#8211; The colourless solution is a complex salt of tetra-hydroxo lead (II) ions (plumbate ions).</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Zn(OH)<sub>2(s)</sub> + 2OH<sup>&#8211;</sup><sub>(aq)</sub> [Zn(OH)<sub>4</sub>]<sup>2-</sup><sub>(aq)</sub></p>
<p><strong><em>(White ppt.) (Colourless solution-tetra hydroxo- lead (II) ion/ plumbate ion)</em></strong></p>
<p> ;</p>
<p> ;</p>
<p><strong>Summary and useful information on qualitative analysis:</strong></p>
<p><strong>Colours of substances in solids and solutions in water.</strong></p>
<p><strong> </strong></p>
<table width="845">
<tbody>
<tr>
<td colspan="2" width="363"><strong>COLOUR</strong></td>
<td rowspan="2" width="482"><strong>IDENTITY</strong></td>
</tr>
<tr>
<td width="131"><strong>SOLID</strong></td>
<td width="233"><strong>AQUESOUS SOLUTION </strong></p>
<p><strong>(IF SOLUBLE)</strong></td>
</tr>
<tr>
<td width="131">1. White</td>
<td width="233">Colourless</td>
<td width="482">Compound of K<sup>+</sup>; Na<sup>+</sup>, Ca<sup>2+</sup>; Mg<sup>2+</sup>; Al<sup>3+</sup>; Zn<sup>2+</sup>; Pb<sup>2+</sup>; NH<sub>4</sub><sup>+</sup></td>
</tr>
<tr>
<td rowspan="2" width="131">2. Yellow</td>
<td width="233">Insoluble</td>
<td width="482">Zinc oxide, ZnO (turns white on cooling); Lead oxide, PbO (remains yellow on cooling, red when hot)</td>
</tr>
<tr>
<td width="233">Yellow</td>
<td width="482">Potassium or sodium chromate;</td>
</tr>
<tr>
<td width="131">3. Blue</td>
<td width="233">Blue</td>
<td width="482">Copper (II) compound, Cu<sup>2+</sup></td>
</tr>
<tr>
<td width="131">4. Pale green</p>
<p> ;</p>
<p>Green</td>
<td width="233">Pale green (almost colourless)</p>
<p>Green</td>
<td width="482">Iron (II) compounds,Fe<sup>2+</sup></p>
<p> ;</p>
<p>Nickel (II) compound, Ni<sup>2+</sup>; Chromium (II) compounds, Cr<sup>3+</sup>; (Sometimes copper (II) compound, Cu<sup>2+</sup>)</td>
</tr>
<tr>
<td width="131">5. Brown</td>
<td width="233">Brown (sometimes yellow)</p>
<p> ;</p>
<p>Insoluble</td>
<td width="482">Iron (III) compounds, Fe<sup>3+</sup>;</p>
<p> ;</p>
<p>Lead (IV) oxide, PbO<sub>2</sub></td>
</tr>
<tr>
<td width="131">6. Pink</td>
<td width="233">Pink (almost colourless)</p>
<p>Insoluble</td>
<td width="482">Manganese (II) compounds, Mn<sup>2+</sup>;</p>
<p>Copper metal as element (sometimes brown but will turn black on heating in air)</td>
</tr>
<tr>
<td width="131">7. Orange</td>
<td width="233">Insoluble</td>
<td width="482">Red lead, Pb<sub>3</sub>O<sub>4</sub> (could also be mercury (II) oxide, HgO)</td>
</tr>
<tr>
<td width="131">8. Black</td>
<td width="233">Purple</p>
<p>Brown</p>
<p>Insoluble</td>
<td width="482">Manganate (VII) ions (MnO<sup>&#8211;</sup>) as in KMnO<sub>4</sub>;</p>
<p>Iodine (element)-purple vapour</p>
<p>Manganese (IV) oxide, MnO<sub>2</sub></p>
<p>Copper (II) oxide, CuO</p>
<p>Carbon powder (element)</p>
<p>Various metal powders (elements)</td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Reactions of cations with common laboratory reagents and solubilities of some salts in water</strong></p>
<p><strong> </strong></p>
<table width="848">
<tbody>
<tr>
<td width="105"><strong>CATION</strong></td>
<td width="165"><strong>SOLUBLE COMPOUNDS (IN WATER)</strong></td>
<td width="173"><strong>INSUOLUBLE COMPOUNDS (IN WATER)</strong></td>
<td width="203"><strong>REACTION WITH AQUEOUS SODIUM HYDROXIDE</strong></td>
<td width="203"><strong>REACTION WITH AQUEOUS AMMONIA SOLUTION</strong></td>
</tr>
<tr>
<td width="105">Na<sup>+</sup></td>
<td width="165">All</td>
<td width="173">None</td>
<td width="203">No reaction</td>
<td width="203">No reaction</td>
</tr>
<tr>
<td width="105">K<sup>+</sup></td>
<td width="165">All</td>
<td width="173">None</td>
<td width="203">No reaction</td>
<td width="203">No reaction</td>
</tr>
<tr>
<td width="105">Ca<sup>2+</sup></td>
<td width="165">Cl<sup>&#8211;</sup>; NO<sub>3</sub><sup>&#8211;</sup>;</td>
<td width="173">CO<sub>3</sub><sup>2-</sup>; O<sup>2-</sup>; SO<sub>4</sub><sup>2-</sup>; OH<sup>&#8211;</sup>;</td>
<td width="203">White precipitate insoluble in excess</td>
<td width="203">White precipitate insoluble in excess, on standing;</td>
</tr>
<tr>
<td width="105">Al<sup>3+</sup></td>
<td width="165">Cl<sup>&#8211;</sup>; NO<sub>3</sub><sup>&#8211;</sup>; SO<sub>4</sub><sup>2-</sup></td>
<td width="173">O<sup>2-</sup>; OH<sup>&#8211;</sup>;</td>
<td width="203">White precipitate soluble in excess</td>
<td width="203">White precipitate insoluble in excess</td>
</tr>
<tr>
<td width="105">Pb<sup>2+</sup></td>
<td width="165">NO<sub>3</sub><sup>&#8211;</sup>; ethanoate;</td>
<td width="173">All others;</td>
<td width="203">White precipitate soluble in excess</td>
<td width="203">White precipitate insoluble in excess</td>
</tr>
<tr>
<td width="105">Zn<sup>2+</sup></td>
<td width="165">Cl<sup>&#8211;</sup>; NO<sub>3</sub><sup>&#8211;</sup>; SO<sub>4</sub><sup>2-</sup></td>
<td width="173">CO<sub>3</sub><sup>2-</sup>; O<sup>2-</sup>; SO<sub>4</sub><sup>2-</sup>; OH<sup>&#8211;</sup>;</td>
<td width="203">White precipitate soluble in excess</td>
<td width="203">White precipitate soluble in excess</td>
</tr>
<tr>
<td width="105">Fe<sup>2+</sup></td>
<td width="165">Cl<sup>&#8211;</sup>; NO<sub>3</sub><sup>&#8211;</sup>; SO<sub>4</sub><sup>2-</sup></td>
<td width="173">CO<sub>3</sub><sup>2-</sup>; O<sup>2-</sup>; OH<sup>&#8211;</sup>;</td>
<td width="203">(Dark) pale green precipitate insoluble in excess</td>
<td width="203">(Dark) pale green precipitate insoluble in excess</td>
</tr>
<tr>
<td width="105">Fe<sup>3+</sup></td>
<td width="165">Cl<sup>&#8211;</sup>; NO<sub>3</sub><sup>&#8211;</sup>; SO<sub>4</sub><sup>2-</sup></td>
<td width="173">CO<sub>3</sub><sup>2-</sup>; O<sup>2-</sup>; OH<sup>&#8211;</sup>;</td>
<td width="203">(Red) brown precipitate insoluble in excess</td>
<td width="203">(Red) brown precipitate insoluble in excess</td>
</tr>
<tr>
<td width="105">Cu<sup>2+</sup></td>
<td width="165">Cl<sup>&#8211;</sup>; NO<sub>3</sub><sup>&#8211;</sup>; SO<sub>4</sub><sup>2-</sup></td>
<td width="173">CO<sub>3</sub><sup>2-</sup>; O<sup>2-</sup>; OH<sup>&#8211;</sup>;</td>
<td width="203">Pale blue precipitate insoluble in excess</td>
<td width="203">Pale blue precipitate soluble in excess forming a deep blue solution</td>
</tr>
<tr>
<td width="105">NH<sub>4</sub><sup>+</sup></td>
<td width="165">All</td>
<td width="173">None;</td>
<td width="203">Ammonias gas on warming</td>
<td width="203">Not applicable.</td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Qualitative analysis for common anions.</strong></p>
<p><strong> </strong></p>
<table>
<tbody>
<tr>
<td width="143"><strong> </strong></td>
<td width="173"><strong>SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub></strong></td>
<td width="184"><strong>Cl<sup>&#8211;</sup><sub>(aq)</sub></strong></td>
<td width="169"><strong>NO<sub>3</sub><sup>&#8211;</sup><sub>(aq)</sub></strong></td>
<td width="169"><strong>CO<sub>3</sub><sup>2-</sup><sub>(aq)</sub></strong></td>
</tr>
<tr>
<td width="143">TEST</td>
<td width="173">Add Ba<sup>2+</sup><sub>(aq)</sub> ions from Ba(NO<sub>3</sub>)<sub>2(aq)</sub>; acidify with dilute HNO<sub>3(aq)</sub></td>
<td width="184">Add Ag<sup>+</sup><sub>(aq)</sub> from AgNO<sub>3(aq)</sub>.</p>
<p>Acidify with dilute HNO<sub>3</sub></p>
<p>Alternatively;</p>
<p>Add Pb<sup>2+</sup> from Pb(NO<sub>3</sub>)<sub>2</sub> and warm</td>
<td width="169">Add FeSO<sub>4(aq)</sub>;</p>
<p>Tilt the tube and carefully add 1-2 cm<sup>3</sup> of concentrated H<sub>2</sub>SO<sub>4(aq)</sub></td>
<td width="169">Add dilute HNO<sub>3(aq)</sub>; bubble gas through lime water;</td>
</tr>
<tr>
<td width="143">OBSERVATION</td>
<td width="173">The formation of a white precipitate shows presence of SO<sub>4</sub><sup>2-</sup> ion;</td>
<td width="184">The formation of a white precipitate shows presence of Cl<sup>&#8211;</sup> ion;</p>
<p>Formation of a white precipitate that dissolves on warming shown presence of Cl<sup>&#8211;</sup><sub>(aq)</sub> ions</td>
<td width="169">The formation of a brown ring shows the presence of NO<sub>3</sub><sup>&#8211;</sup> ions</td>
<td width="169">Evolution of a colourless gas that forma a white precipitate with lime water, turns moist blue litmus paper red; and extinguishes a glowing splint shows presence of CO<sub>3</sub><sup>2-</sup> ions</td>
</tr>
<tr>
<td width="143">EXPLANATION</td>
<td width="173">Only BaSO<sub>4</sub> and BaCO<sub>3</sub> can be formed as white precipitates.</p>
<p>BaCO<sub>3</sub> is soluble in dilute acids and so BaSO<sub>4</sub> will remain on adding dilute nitric acid</td>
<td width="184">Only AgCl and AgCO<sub>3</sub> can be formed as white precipitates.</p>
<p>AgCO<sub>3</sub> is soluble in dilute acids but AgCl is not;</p>
<p>&#8211; PbCl<sub>2</sub> is the only white precipitate that dissolves on warming</td>
<td width="169">Concentrated H<sub>2</sub>SO<sub>4</sub> forms nitrogen (II) oxide with NO<sub>3</sub><sup>&#8211;</sup><sub>(aq)</sub> and this forms brown ring complex (FeSO<sub>4</sub>.NO) with FeSO<sub>4</sub>;</td>
<td width="169">All CO<sub>3</sub><sup>2-</sup> or HCO<sub>3</sub><sup>&#8211;</sup> will liberate carbon (IV) oxide with dilute acids</td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p><strong>Checklist:</strong></p>
<ol>
<li>Why is it not possible to use dilute sulphuric acid in the test for SO<sub>4</sub><sup>2-</sup> ions;</li>
<li>Why is it not possible to use dilute hydrochloric acid in the test for chloride ions?</li>
<li>Why is it best to use dilute nitric acid instead of the other two mineral acids in the test for CO<sub>3</sub><sup>2- </sup>ions?</li>
<li>How would you distinguish two white solids, Na<sub>2</sub>CO<sub>3</sub> and NaHCO<sub>3</sub>?</li>
</ol>
<p> ;</p>
<p><strong>What to look for when a substance is heated.</strong></p>
<p> ;</p>
<table width="857">
<tbody>
<tr>
<td width="434">1. Sublimation</td>
<td width="423">White solids on cool, parts of a test tube indicates NH<sub>4</sub><sup>+</sup> compounds;</p>
<p>Purple vapour condensing to black solid indicates iodine crystals;</td>
</tr>
<tr>
<td width="434">2. Water vapour (condensed)</td>
<td width="423">Colourless droplets on cool parts of the test tube indicate water of crystallization or HCO<sub>3</sub><sup>&#8211;</sup> (see below)</td>
</tr>
<tr>
<td width="434">3. Carbon (IV) oxide</td>
<td width="423">CO<sub>3</sub><sup>2-</sup> of Zn<sup>2+</sup>; Pb<sup>2+</sup>; Fe<sup>2+</sup>; Fe<sup>3+</sup>; Cu<sup>2+</sup>;</td>
</tr>
<tr>
<td width="434">4. Carbon (IV) oxide and water vapour (condensed)</td>
<td width="423">HCO<sub>3</sub><sup>&#8211;</sup></td>
</tr>
<tr>
<td width="434">5. Nitrogen (IV) oxide</td>
<td width="423">NO<sub>3</sub><sup>&#8211; </sup>of Cu<sup>2+</sup>; Al<sup>3+</sup>; Zn<sup>2+</sup>; Pb<sup>2+</sup>; Fe<sup>2+</sup>; Fe<sup>3+</sup></td>
</tr>
<tr>
<td width="434">6. Oxygen</td>
<td width="423">NO<sub>3</sub><sup>&#8211;</sup> or BaO<sub>2</sub>; MnO<sub>2</sub>; PbO<sub>2</sub>;</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Industrial manufacture of ammonia-The Haber process.</strong></p>
<p><strong> </strong></p>
<p>&#8211; Most of the worldÂs supply of ammonia is from the synthesis of Nitrogen and hydrogen in the Haber process.</p>
<p> ;</p>
<p><strong>(i). Raw materials</strong></p>
<p> ;</p>
<ul>
<li><strong>Nitrogen</strong></li>
</ul>
<p>&#8211; Usually obtained from liquid air by fractional distillation</p>
<p> ;</p>
<ul>
<li><strong>Hydrogen</strong></li>
</ul>
<p>&#8211; Obtained from water gas in the <strong>Bosch process.</strong></p>
<p>&#8211; Also from crude oil (cracking)</p>
<p> ;</p>
<p><strong>(ii). General equation</strong></p>
<p> ;</p>
<p>N<sub>2(g)</sub> + 3 H<sub>2(g)</sub> 2NH<sub>3(g)</sub> + heat;</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Nitrogen and hydrogen combine in the ratio 1:3 respectively to form two volumes of ammonia gas plus heat.</p>
<p>-The reaction is <strong>exothermic</strong> releasing heat to the surrounding.</p>
<p><em> </em></p>
<p><strong><em>(</em>iii). Conditions</strong></p>
<p><strong><em> </em></strong></p>
<ul>
<li><strong>High pressures</strong></li>
</ul>
<p>&#8211; The process is favoured by high pressures and thus a pressure of approximately 200 to 300 atmospheres is used.</p>
<p> ;</p>
<p><strong>Reason: </strong></p>
<p>&#8211; The volume of gaseous reactants from equation is higher than volume of gaseous products. Thus increased pressure shifts the equilibrium to the right; favoring the production of more ammonia.</p>
<p><strong>Note: </strong></p>
<p>Such high pressures are however uneconomical.</p>
<p><em><u> </u></em></p>
<ul>
<li><strong>Low temperatures</strong></li>
</ul>
<p>&#8211; Low temperatures favour production of ammonia;</p>
<p><strong>Reason:</strong></p>
<p>&#8211; The reaction is exothermic (releases heat to the surrounding) hence lower temperature will favour the forward reaction (shift the equilibrium to the right), producing more ammonia.</p>
<p><em> </em></p>
<ul>
<li><strong>Catalyst</strong></li>
</ul>
<p>&#8211; The low temperatures make the reaction slow and therefore a catalyst is used to increase the rate of reaction</p>
<p>&#8211; The catalyst used is <strong>finely divided iron</strong>; impregnated with Aluminium oxide (Al<sub>2</sub>O<sub>3</sub>)</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(iv). The chemical processes</strong></p>
<p><strong> </strong></p>
<p><strong>Step 1: Purification</strong></p>
<p>-The raw materials, nitrogen and hydrogen are passed through a purification chamber in which impurities are removed.</p>
<p>-The main impurities are CO<sub>2</sub>, water vapour, dust particles, SO<sub>2</sub>, CO<sub>2</sub> and O<sub>2</sub>;</p>
<p><em> </em></p>
<p><strong>Reason:</strong></p>
<p>The impurities would poison the catalyst</p>
<p><em> </em></p>
<p><strong>Step 2: Compression</strong></p>
<p>&#8211; The purified Nitrogen and Hydrogen gases are compressed in a compressor at 500 atmospheres.</p>
<p><strong> </strong></p>
<p><strong>Reasons:</strong></p>
<ul>
<li>To increase chances of molecules reacting;</li>
<li>To increase rate of <strong>collision</strong> of the reacting particles.</li>
<li>To increase pressure (attain desired pressures); and hence increase concentration of reacting particles.</li>
</ul>
<p><strong><em> </em></strong></p>
<p><strong>Step 3: Heat exchanger reactions</strong></p>
<p>&#8211; Upon compression the gaseous mixture, nitrogen and hydrogen are channeled into a heat exchanger; which <strong>heats them</strong> increasing their temperature.</p>
<p>&#8211; This enables the reactants (hydrogen and nitrogen) to attain the <strong>optimum temperatures</strong> for the succeeding reactions (in the catalytic chamber)</p>
<p>&#8211; From the heat exchanger the gases go to the catalyst chamber.</p>
<p><strong><em> </em></strong></p>
<p><strong>Step 4: Catalytic chamber.</strong></p>
<p>&#8211; The gases then combine in the ratio of 1:3 (N<sub>2</sub>:H<sub>2 </sub>respectively), to form ammonia.</p>
<p>&#8211; This reaction occurs in presence of a <strong>catalyst</strong>; which speeds up the rate of ammonia formation;</p>
<p>&#8211; The catalyst is <strong>finely divided iron</strong> impregnated with <strong>aluminium oxide </strong>(Al<sub>2</sub>O<sub>3</sub> increases the catalytic activity of iron).</p>
<p> ;</p>
<p><strong>Equation in catalytic chamber</strong></p>
<p><strong> </strong></p>
<p>N<sub>2(g)</sub> + 3H<sub>2(g) </sub> 2NH<sub>3(g)</sub> + Heat (-92kjmol<sup>&#8211;</sup>)</p>
<p> ;</p>
<p>&#8211; Only about 6-10% of the gases combine.</p>
<p>&#8211; Due to the high heat evolution involved, the products are again taken back to the heat exchanger; to cool the gases coming from the catalytic chamber.</p>
<p><em> </em></p>
<p><strong>Step 5: Heat exchanger</strong></p>
<p>&#8211; The gases from the catalytic chamber enter the heat exchanger a second time.</p>
<p><strong> </strong></p>
<p><strong>Reason:</strong></p>
<p>&#8211; To <strong>cool</strong> the gases coming from the catalytic chamber, thus reduce cost of condensation.</p>
<p>-The gaseous mixture; ammonia and uncombined nitrogen and hydrogen are the passed through a condenser.</p>
<p><strong><em> </em></strong></p>
<p><strong>Step 6: The condenser reactions (cooling chamber)</strong></p>
<p>&#8211; The pressure and the low temperatures in this chamber liquefy ammonia, which is then drawn off.</p>
<p>&#8211; The uncombined (unreacted) gases are recirculated back to the compressor, from where they repeat the entire process.</p>
<p><strong>Summary: flow chart of Haber process.</strong></p>
<table>
<tbody>
<tr>
<td width="0"></td>
<td width="126"></td>
<td width="78"></td>
<td width="78"></td>
<td width="102"></td>
<td width="90"></td>
<td width="42"></td>
<td width="150"></td>
</tr>
<tr>
<td></td>
<td width="126">
<table width="100%">
<tbody>
<tr>
<td>Fractional distillation of air</td>
</tr>
</tbody>
</table>
</td>
<td></td>
<td rowspan="2" width="78">
<table width="100%">
<tbody>
<tr>
<td>Nitrogen</td>
</tr>
</tbody>
</table>
</td>
<td></td>
<td rowspan="2" width="90">
<table width="100%">
<tbody>
<tr>
<td>Hydrogen</td>
</tr>
</tbody>
</table>
</td>
<td></td>
<td rowspan="2" width="150">
<table width="100%">
<tbody>
<tr>
<td>Crude oil cracking; or water gas in Bosch process</td>
</tr>
</tbody>
</table>
</td>
</tr>
<tr>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="311"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Purifier</strong>: removal of duct particles; CO<sub>2</sub>; H<sub>2</sub>O vapour etc</p>
<table>
<tbody>
<tr>
<td width="95"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p>Unreacted gases</p>
<p>(recycling)</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p>6-10% ammonia + air;</p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="239"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>LIQUID AMMONIA</strong></p>
<p> ;</p>
<p> ;</p>
<p><strong>Citing a Haber process plant</strong></p>
<p>&#8211; When choosing a site for this industrial plant, the following factors are considered:</p>
<ol>
<li>Availability of raw materials (natural gas and crude oil)</li>
<li>Presence of cheap sources of energy.</li>
<li>Availability of transport and marketing.</li>
<li>Availability of appropriate technology and labour force.</li>
</ol>
<p><strong><u> </u></strong></p>
<p><strong>Ammonium salts as fertilizers</strong></p>
<p>&#8211; Ammonium salts are prepared by the reaction between ammonia and the appropriate acid in dilute solution followed by evaporation and crystallization</p>
<p><strong> </strong></p>
<p><strong>(a). Ammonium sulphate </strong></p>
<p>&#8211; Is prepared by absorbing ammonia in sulphuric acid.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p><strong> </strong></p>
<p>2NH<sub>3(g)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> (NH<sub>4</sub>)<sub>2</sub>SO<sub>4(aq)</sub></p>
<p> ;</p>
<p><strong>Note:</strong> It is a cheap fertilizer.</p>
<p> ;</p>
<p>(<strong>b). Ammonium nitrate</strong></p>
<p>&#8211; Is prepared by neutralization nitric acid by ammonia.</p>
<p><strong> </strong></p>
<p><strong>Equation</strong>:</p>
<p> ;</p>
<p>NH<sub>3(g)</sub> + HNO<sub>3(aq)</sub> NH<sub>4</sub>NO<sub>3(aq)</sub></p>
<p> ;</p>
<p>&#8211; As there is some danger of exploding during storage, ammonium nitrate is mixed with finely powdered limestone (CaCO<sub>3</sub>).</p>
<p>-The mixture, sold as nitro-chalk is much safer.</p>
<p>(<strong>c). Ammonium phosphate</strong></p>
<p>&#8211; It is particularly useful as it supplies both nitrogen and phosphorus to the soil.</p>
<p>&#8211; It is prepared by neutralizing <strong>othophosphoric</strong> acid by ammonia</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p><strong> </strong></p>
<p>3NH<sub>3(g)</sub> + H<sub>3</sub>PO<sub>4(aq)</sub> (NH<sub>4</sub>)<sub>3</sub> PO<sub>4(aq)</sub></p>
<p> ;</p>
<p><strong>(d) Urea CO (NH<sub>2</sub>)<sub>2</sub></strong></p>
<p>&#8211; Is made from ammonia and carbon (IV) oxide</p>
<p>&#8211; Its nitrogen content by mass is very high; nearly 47%</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p><em><u> </u></em></p>
<p>NH<sub>3(g)</sub> +CO<sub>2(g)</sub> CO (NH<sub>2</sub>)<sub>2(aq) </sub>+ H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong> </strong></p>
<p><strong>Nitric (V) acid</strong></p>
<p>&#8211; Is a monobasic acid (has only one replaceable Hydrogen atom); and has been known as strong water (aqua forty).</p>
<p>&#8211; It is a compound of hydrogen, oxygen and nitrogen.</p>
<p><strong><u> </u></strong></p>
<p><strong>Laboratory preparation of nitric (V) acid </strong></p>
<p><strong>(i). Apparatus</strong></p>
<p><strong> </strong></p>
<p><strong>(ii). Reagents</strong></p>
<p>&#8211; Nitric acid is prepared in the laboratory by action of concentrated sulphuric acid on solid nitrates e.g. potassium nitrate (KNO<sub>3</sub>) and sodium nitrate (NaNO<sub>3</sub>)</p>
<p><strong> </strong></p>
<p><strong>(iii). Procedure</strong></p>
<p>&#8211; 30-40 grams of small crystal of KNO<sub>3</sub> are put in a retort flask.</p>
<p>&#8211; Concentrated sulphuric acid is added just enough to cover the nitrate; and then heated (warmed) gently.</p>
<p>&#8211; The apparatus is all glass.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; Nitric (V) acid would attack rubber connections.</p>
<p>&#8211; The neck of the retort flask is inserted into a flask that is kept cool continually under running water; this is where nitric acid is collected.</p>
<p><strong> </strong></p>
<p><strong>Note:</strong></p>
<p>The cold water running over the collection flask is meant to cool (condense) the hot fumes of nitric (V) acid.</p>
<p><strong> </strong></p>
<p><strong>(iv). Observations and explanations</strong></p>
<p>&#8211; Fumes of nitric are observed in the retort;</p>
<p><strong> </strong></p>
<p><strong>Equation</strong></p>
<p><strong> </strong></p>
<p>KNO<sub>3(g)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> KHSO<sub>4(aq)</sub> +HNO<sub>3(g)</sub></p>
<p> ;</p>
<p>&#8211; If Lead (II) nitrate was used;</p>
<p> ;</p>
<p>Pb(NO<sub>3</sub>)<sub>2(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> PbSO<sub>4(s)</sub> + 2HNO<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>Note:</strong> with lead (II) nitrate the reaction soon stops because the insoluble lead (II) sulphate coats the surface of the nitrate preventing further reaction; yield of nitric (V) acid is thus lower;</p>
<p> ;</p>
<p>-These fumes of nitric acid appear brown.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; Due to the presence of nitrogen (iv) oxide gas formed by thermal decomposition of nitric acid.</p>
<p> ;</p>
<p><strong>Equation:</p>
<p></strong></p>
<p>4HNO<sub>3(aq)</sub> 4NO<sub>2(g)</sub> + O<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(g)</sub></p>
<p> ;</p>
<p>&#8211; Pure nitric (V) acid is colourless but may appear yellow (brown) due to the presence of Nitrogen (IV) oxide.</p>
<p>&#8211; The brown colour can be removed by blowing air through the acid.</p>
<p>&#8211; Fuming nitric acid boils at 83<sup>o</sup>C and is 99% pure; while concentrated nitric acid is only 70% acid and 30% water.</p>
<p> ;</p>
<p><strong>Note</strong>: Nitric acid is usually stored in dark bottles.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; To avoid its decomposition by light to nitrogen (IV) oxide, oxygen and water.</p>
<p>&#8211; The reaction in the retort flask is a typical displacement reaction; in which the more volatile nitric (V) acid is displaced from nitrates by the less volatile sulphuric acid.</p>
<p>&#8211; The nitric acid distills over because it is more volatile than sulphuric acid.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><em> </em></p>
<p> ;</p>
<p><strong>Properties of concentrated nitric acid</strong></p>
<p>&#8211; Nitric (V) acid readily gives oxygen and therefore is called an oxidizer.</p>
<p>&#8211; The acid is usually reduced to nitrogen (IV) oxide and water.</p>
<p> ;</p>
<ol>
<li><strong> Effects of heat on concentrated nitric acid</strong></li>
</ol>
<p><strong>(i) Apparatus</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii) Observations</strong></p>
<p>&#8211; Brown fumes are seen in the hard glass tube.</p>
<p>&#8211; Colourless gas is collected over water.</p>
<p><strong><em> </em></strong></p>
<p><strong>(ii). Explanations</strong></p>
<p>&#8211; Sand soaked in concentrated nitric acid produces nitric solid vapour on heating.</p>
<p>&#8211; The hot glass wool catalyzes the decomposition of nitric acid to nitrogen (IV) oxide (brown fumes), water vapour and oxygen.</p>
<p><strong> </strong></p>
<p><strong>Equation</strong></p>
<p><strong> </strong></p>
<p>4HNO<sub>3(l)</sub> 4NO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + O<sub>2(g)</sub></p>
<p><strong><em> (Brown fumes)</em></strong></p>
<p> ;</p>
<p>&#8211; The so formed nitrogen (IV) oxide dissolves in water forming both nitric and nitrous acids.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p> ;</p>
<p>2NO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> HNO<sub>2(aq)</sub> + HNO<sub>3(aq)</sub></p>
<p><sub> </sub></p>
<p>&#8211; The oxygen gas is collected over water; and with the solution becoming acidic.</p>
<p><strong> </strong></p>
<ol start="2">
<li><strong> Reaction with saw dust</strong></li>
</ol>
<p>&#8211; Saw dust contains compounds of carbon Hydrogen and oxygen.</p>
<p><strong> </strong></p>
<p><strong>Procedure:</strong></p>
<p>&#8211; Some saw dust is heated in an evaporating dish and some few drops of concentrated nitric (V) acid on it (this is done in a fume cupboard)</p>
<p><strong><em> </em></strong></p>
<p><strong>Observation:</strong></p>
<p>&#8211; A violent reaction occurs, the saw dust catches fire easily and a lot of brown fumes of nitrogen (IV) oxide given off.</p>
<p>&#8211; Nitric (V) acid oxidizes the compounds in saw dust to CO<sub>2</sub> and water; and itself it is reduced to nitrogen (IV) oxide and water.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>(C, H, O)<sub> n(s)</sub> + HNO<sub>3(l)</sub> NO<sub>2(g)</sub> + CO<sub>2(g)</sub> +H<sub>2</sub>O<sub>(g)</sub></p>
<p><strong><em>Saw dust</em></strong></p>
<p> ;</p>
<p>&#8211; Warm concentrated nitric (V) acid oxidizes pure carbon and many other compounds containing carbon.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>C<sub>(s)</sub> + 4HNO<sub>3(l)</sub> 2H<sub>2</sub>O<sub>(l)</sub> + 4NO<sub>2(g)</sub> + CO<sub>2(g)</sub></p>
<p> ;</p>
<ol start="3">
<li><strong> Reaction with sulphur</strong></li>
</ol>
<p><strong>Procedure:</strong></p>
<p>&#8211; 2 cm<sup>3 </sup>of concentrated nitric (V) acid is added to a little sulphur in a test tube and warmed.</p>
<p>&#8211; The mixture is filtered to remove excess sulphur and the filtrate diluted with distilled water.</p>
<p>&#8211; Drops of barium chloride are then added to the resultant solution.</p>
<p><strong><em> </em></strong></p>
<p><strong>Observations:</strong></p>
<p>&#8211; Red brown gas, nitrogen (IV) oxide (NO<sub>2</sub>) is evolved and the sulphur is oxidized to sulphuric acid.</p>
<p><strong> </strong></p>
<p><strong>Equation </strong></p>
<p>S<sub>(s)</sub> + 6HNO<sub>3(l)</sub> H<sub>2</sub>SO<sub>4(aq)</sub> + 6NO<sub>2(g)</sub> +2H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>&#8211; On addition of barium chloride to the solution, a white precipitate is formed.</p>
<p>&#8211; This is due to formation of barium sulphate and is a confirmation for the presence of SO<sub>4</sub><sup>2</sup>&#8211; ions.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p> ;</p>
<p>Ba<sup>2+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> BaSO<sub>4(s)</sub></p>
<p><strong> </strong><strong><em>(White precipitate)</em></strong></p>
<p><strong> </strong></p>
<ol start="4">
<li><strong> Reaction with metals</strong></li>
</ol>
<p>&#8211; Concentrated nitric (V) acid reacts with metals except <strong>gold</strong> and <strong>platinum</strong>.</p>
<p>&#8211; Actual reaction depends on the concentration of the acid and the position of the metal in the reactivity series.</p>
<p>&#8211; The reaction results in a metal nitrate, NO<sub>2 </sub>and water.</p>
<p>&#8211; Copper, which is low in the reactivity series, reduces conc. HNO<sub>3</sub> to NO<sub>2</sub>.</p>
<p><strong><em> </em></strong></p>
<p><strong>Equation:</strong></p>
<p><strong><em> </em></strong></p>
<p>C<sub>u(s)</sub> + HNO<sub>3(l)</sub> C<sub>u</sub>(NO<sub>3</sub>)<sub>2(aq)</sub> + 2NO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>&#8211; Metals more reactive than copper e.g. Magnesium may reduce nitric acid to dinitrogen monoxide (N<sub>2</sub>O) or Nitrogen (N<sub>2</sub>).</p>
<p>&#8211; Some metals like iron and aluminium form insoluble layers when reacted with nitric acid thus stopping any further reaction.</p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<ol start="5">
<li><strong> Reaction with iron (II) salts</strong></li>
</ol>
<p><strong><em> </em></strong></p>
<p><strong>Procedure:</strong></p>
<p>&#8211; Few crystals of iron (II) sulphate are dissolved in dilute sulphuric acid.</p>
<p>&#8211; A little concentrated nitric (V) acid is added to the solution and mixture warmed.</p>
<p><strong><em> </em></strong></p>
<p><strong>Observation:</strong></p>
<p>&#8211; Green solution turns brown.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p> ;</p>
<p>6FeSO<sub>4(s)</sub> + 3H<sub>2</sub>SO<sub>4(aq)</sub> +3HNO<sub>3(l)</sub> 4H<sub>2</sub>O<sub>(l)</sub> +2NO<sub>(g)</sub> + 3Fe<sub>2</sub> (SO<sub>4</sub>)<sub>3(aq)</sub></p>
<p><strong><em> </em></strong></p>
<p><strong>Explanation:</strong></p>
<p>&#8211; Nitric acid oxidizes green iron (II) salts (Fe<sup>2+</sup>) to brown iron (III) salts (Fe<sup>3+</sup>) and itself is reduced to Nitrogen (II) Oxide.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; In air, nitrogen (II) oxide is readily oxidized to nitrogen (IV) oxide; resulting to brown fumes.</p>
<p> ;</p>
<p>Equation:<br />
2NO<sub>(g)</sub> + O<sub>2(g) </sub> 2NO<sub>2(g)</sub></p>
<p><strong><u> </u></strong></p>
<ol start="6">
<li><strong> Reduction of nitric (V) acid by hydrogen sulphide.</strong></li>
</ol>
<p><strong>Procedure</strong></p>
<p>&#8211; A few drops of conc. nitric (V) acid are added to a gas jar full of hydrogen sulphide and the jar then covered.</p>
<p><strong><em> </em></strong></p>
<p><strong>Observations</strong></p>
<p>&#8211; Fumes (brown) of Nitrogen (IV) oxide and yellow deposits of sulphur;</p>
<p><strong><em> </em></strong></p>
<p><strong>Equation</strong></p>
<p>&#8211; It is a REDOX reaction.</p>
<p><strong><em>Oxidation</em></strong></p>
<table>
<tbody>
<tr>
<td width="11"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>H<sub>2</sub>S<sub>(g)</sub> + 2HNO<sub>3(l)</sub> 2H<sub>2</sub>O<sub>(l)</sub> + 2NO<sub>2(g)</sub> +S<sub>(s)</sub></p>
<p> ;</p>
<p> ;</p>
<p><strong><em>Reduction</em></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong>Properties of dilute nitric (V) acid</strong></p>
<ol>
<li><strong> Reaction with metals</strong></li>
</ol>
<p>&#8211; Dilute nitric (V) acid reacts with most metals to form nitrogen (II) oxide instead of hydrogen.</p>
<p> ;</p>
<p><strong>Example:</strong></p>
<p>3Mg<sub>(s)</sub> + 8HNO<sub>3(aq)</sub> 3Mg(NO<sub>3</sub>)<sub>2(aq)</sub> +2NO<sub>(g)</sub> + 4H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p>&#8211; In fact HNO<sub>3 </sub>is reduced to NO and water but NO soon gets oxidized in air to form brown fumes of NO<sub>2</sub>.</p>
<p>&#8211; However very dilute HNO<sub>3 </sub>(cold) reacts with more active metals such as Magnesium to produce <strong>Hydrogen.</strong></p>
<p> ;</p>
<ol start="2">
<li><strong>Dilute nitric (V) acid as a typical acid</strong></li>
</ol>
<p>(a). It turns blue litmus paper red.</p>
<p>(b). It reacts with metal oxides and metal hydroxides to form a metal nitrate and water (Neutralization)</p>
<p><strong><em> </em></strong></p>
<p><strong>Examples</strong></p>
<ul>
<li>CuO<sub>(s)</sub> + 2HNO<sub>3(aq)</sub> Cu (NO<sub>3</sub>)<sub>2(aq) </sub>+ H<sub>2</sub>O<sub>(l)</sub></li>
</ul>
<p><strong><em> (Black) (Blue)</em></strong></p>
<p> ;</p>
<ul>
<li>Zn(OH)<sub>2(s)</sub> + 2HNO<sub>3(aq)</sub> Zn (NO<sub>3</sub>)<sub>2(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></li>
</ul>
<p><strong><em> (White ppt) (Colourless)</em></strong></p>
<p> ;</p>
<ul>
<li>KOH<sub>(aq)</sub> + HNO<sub>3(aq)</sub> KNO<sub>3(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></li>
</ul>
<p><strong><em> (Alkali) (Acid) (Salt) (Water)</em></strong></p>
<p><strong><u> </u></strong></p>
<ol start="3">
<li><strong> Reaction with metal carbonates and hydrogen carbonates</strong></li>
</ol>
<p>&#8211; Dilute HNO<sub>3 </sub>reacts with metal carbonates and hydrogen carbonates to form a nitrate, CO<sub>2 </sub>and water.</p>
<p> ;</p>
<p><strong>Examples.</strong></p>
<p>CuCO<sub>3</sub>(s) + 2HNO<sub>3(aq)</sub> Cu(NO<sub>3</sub>)<sub>2(aq)</sub> + CO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(Green) (Blue solution)</em></strong></p>
<p> ;</p>
<p>NaHCO<sub>3(s)</sub> + HNO<sub>3(aq)</sub> NaNO<sub>3(aq)</sub> + CO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong> </strong></p>
<p><strong>Test for nitrates/nitric acid</strong></p>
<ol>
<li><strong> Oxidation of iron (ii) sulphate</strong></li>
</ol>
<p>&#8211; Concentrated HNO<sub>3</sub> oxidizes green Iron (II) sulphate in presence of sulphuric acid into Iron (III) sulphate (yellow/brown)</p>
<p>&#8211; However the solution turns dark brown due to formation of a compound, FeSO<sub>4</sub>.NO</p>
<p>&#8211; NO is produced by reduction of nitrate to nitrogen monoxide by Fe<sup>2+</sup></p>
<p><strong><em> </em></strong></p>
<p><strong>Ionically;</strong></p>
<p>Fe<sup>2</sup><sub>+(aq)</sub> Fe<sup>3+</sup><sub>(aq) </sub><sup> </sup> + e<sup>&#8211;</sup> (oxidized)</p>
<p> ;</p>
<p>NO<sub>3</sub><sup>&#8211;</sup><sub>(aq)</sub> + 2H<sup>+</sup><sub>(aq)</sub> + e<sup>&#8211;</sup> NO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> (reduced)</p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<p><strong><u> </u></strong></p>
<ol start="2">
<li><strong> Brown ring test</strong></li>
</ol>
<p><strong>Procedure.</strong></p>
<p>&#8211; An unknown solid is dissolved then acidified using dilute H<sub>2</sub>SO<sub>4</sub>.</p>
<p>&#8211; Some FeSO<sub>4</sub> solution is then added.</p>
<p>&#8211; The test tube is then held at an angle and concentrated sulphuric (V) acid is added slowly (dropwise) to the mixture.</p>
<p><strong><em> </em></strong></p>
<p><strong>Observations</strong></p>
<p>&#8211; The oily liquid (conc. H<sub>2</sub>SO<sub>4</sub>) is denser than water hence sinks to the bottom.</p>
<p>&#8211; A brown ring forms between the two liquid layers if the solid is a nitrate.</p>
<p><strong> </strong></p>
<p><strong>Diagrams:</strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Explanations:</strong></p>
<p>&#8211; Suppose the solution tested isKNO<sub>3</sub>, the conc. H<sub>2</sub>SO<sub>4 </sub>and the KNO<sub>3 </sub>reacted to produce HNO<sub>3</sub>.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>KNO<sub>3</sub>(aq) +H<sub>2</sub>SO<sub>4(aq)</sub> KHSO<sub>4(aq)</sub> + HNO<sub>3(aq)</sub></p>
<p> ;</p>
<p>&#8211; The NO<sub>3</sub><sup>&#8211;</sup> from nitric acid oxidizes some of the FeSO<sub>4</sub> to Fe<sub>2 </sub>(SO<sub>4</sub>)<sub>3</sub> (Fe<sup>2+</sup> toFe<sup>3+</sup>) and itself reduced to NO by the Fe<sup>2+</sup></p>
<p> ;</p>
<p>-The NO so formed reacts with more FeSO4 to give a brown compound (FeSO4 NO) which appears as a brown ring.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>FeSO<sub>4(aq)</sub> + NO<sub>(g)</sub> FeSO<sub>4</sub>. NO<sub>(aq)</sub></p>
<p><strong><em>(Green) (Brown)</em></strong></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>Fe<sup>2+</sup><sub>(aq)</sub> + 5H<sub>2</sub>O<sub>(l)</sub> + NO<sub>(g)</sub> [Fe(H<sub>2</sub>O)<sub>5</sub>NO]<sup>2+</sup><sub>(aq)</sub></p>
<p><strong><em>(Green) (Brown)</em></strong></p>
<p><strong><u> </u></strong></p>
<ol start="3">
<li><strong> Heat</strong></li>
</ol>
<p>&#8211; Nitrates of less reactive metals decompose easily with gentle heating; clouds of brown NO<sub>2</sub> can be seen.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2Cu(NO<sub>3</sub>)<sub>2 </sub> <sup>heat </sup> 2CuO<sub>(s)</sub> + 4NO<sub>2(g)</sub> + O<sub>2(g)</sub></p>
<p><strong><em> (Brown, acidic)</em></strong></p>
<p>&#8211; The nitrates of more reactive metals need much stronger heating and decompose in a different way.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2Na NO<sub>3(s)</sub> <sup> heat </sup> 2NaNO<sub>2(s)</sub> + O<sub>2(g)</sub></p>
<p> ;</p>
<p><strong><u> </u></strong></p>
<p><strong>Uses of nitric acid </strong></p>
<p>&#8211; Large quantities are used in fertilizer manufacture.</p>
<p>&#8211; Manufacture of explosives (TNT)</p>
<p>&#8211; Manufacture of dyes</p>
<p>&#8211; Making nitrate salts</p>
<p>&#8211; Etching of metals.</p>
<p>&#8211; Manufacture of nylon and terylene</p>
<p>&#8211; Refining precious metals</p>
<p>&#8211; An oxidizing agent.</p>
<p> ;</p>
<p><strong>Industrial manufacture of nitric acid</strong></p>
<p><strong>The OtswaldÂs process</strong></p>
<p><strong> (a). Introduction</strong></p>
<p>&#8211; Nitric acid is manufactured by the catalyst oxidation of ammonia and dissolving the products in water.</p>
<p><strong> </strong></p>
<p><strong>(b). Raw materials</strong></p>
<p>&#8211; Atmosphere air</p>
<p>&#8211; Ammonia from Haber process.</p>
<p><strong> </strong></p>
<p><strong>(c). Conditions</strong></p>
<p>&#8211; <strong>Platinum-rhodium</strong> catalyst or platinum gauze.</p>
<p>&#8211; The ammonia-air mixture must be cleaned (purified) to remove dust particles which could otherwise poison the catalyst.</p>
<p><strong> </strong></p>
<p><strong>(d). Chemical reactions</strong>.</p>
<p><strong>Step 1: Compressor reactions.</strong></p>
<p>&#8211; Ammonia and excess air (oxygen) (1:10 by volume) is slightly compressed.</p>
<p>&#8211; The mixture is then cleaned to remove particles which would otherwise <strong>poison</strong> the catalyst.</p>
<p>&#8211; They are then passed to the heat exchanger.</p>
<p><em> </em></p>
<p><strong>Step 2: Heat exchanger and catalytic chamber.</strong></p>
<p>&#8211; In the heat exchanger, the gaseous mixture is heated to about 900<sup>o</sup>C and then passed over a platinum-rhodium catalytic chamber.</p>
<p>&#8211; An <strong>exothermic</strong> reaction occurs and ammonia is oxidized to <strong>nitrogen (II) oxide</strong> and <strong>steam</strong>.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>4NH<sub>3(g)</sub> + 5O<sub>2(g)</sub> 4NO<sub>(g)</sub> + 6H<sub>2</sub>O<sub>(g)</sub> + Heat.</p>
<p> ;</p>
<p>&#8211; The exothermic reaction once started, provides the <strong>heat</strong> necessary to maintain the required <strong>catalytic temperature</strong>.</p>
<p>-This is of <strong>economical advantage</strong> i.e. electrical heating of catalyst is not continued hence lowering production costs.</p>
<p><strong><em> </em></strong></p>
<p><strong>Step 3: Heat exchanger.</strong></p>
<p>&#8211; The hot products from catalytic chamber are again passed back through the heat exchanger.</p>
<p>&#8211; The hot gases are cooled and then passed into the cooling chamber.</p>
<p><strong><em> </em></strong></p>
<p><strong> </strong></p>
<p><strong>Step 4: Cooling chamber</strong></p>
<p><strong><em>&#8211; </em></strong>Once cooled, the NO is oxidized to NO<sub>2</sub> by reacting it with excess oxygen.</p>
<p><em> </em></p>
<p><strong>Equation:</strong></p>
<p> ;</p>
<p>2NO<sub>(g)</sub> + O<sub>2(g)</sub> 2NO<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Step 5: Absorption towers:</strong></p>
<p>&#8211; The NO<sub>2</sub> in excess air is then passed through a series of absorption towers where they meet a stream of hot water and form nitric (V) acid and nitrous (III) acid.</p>
<p><strong><em> </em></strong></p>
<p><strong>Equations:</strong></p>
<p>2NO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> HNO<sub>3(aq)</sub> + HNO<sub>2(aq)</sub> (blue solution)</p>
<p><strong><em> Nitric Nitrous</em></strong></p>
<p> ;</p>
<p>&#8211; The so produced nitrous (III) acid is oxidized by oxygen in excess air to nitric (V) acid so that the concentration of nitric acid in the solution (liquid) gradually increases.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2 HNO<sub>2(aq)</sub> + O<sub>2(g)</sub> 2HNO<sub>3(aq)</sub></p>
<p> ;</p>
<p>&#8211; The resultant HNO<sub>3</sub> is only 55%-65% concentrated.</p>
<p>&#8211; It is made more concentrated by careful distillation of the solution.</p>
<p><strong> </strong></p>
<p><strong>The process of distillation (increasing the concentration).</strong></p>
<p>&#8211; Concentrated sulphuric (VI) acid is added to the dilute nitric (V) acid.</p>
<p>&#8211; The heat produced (when dilute sulphuric acid reacts with water) vapourises the nitric (V) acid.</p>
<p>&#8211; The resultant nitric (V) acid vapour is condensed.</p>
<p><strong>Note</strong>:</p>
<ul>
<li>Nitric (V) acid is stored in dark bottles.</li>
</ul>
<p><strong>Reason:</strong></p>
<p>&#8211; To prevent its <strong>decomposition</strong> since it undergoes slow decomposition when exposed to light.</p>
<p> ;</p>
<ul>
<li>Dilute nitric (V) acid has higher ions concentration than concentrated nitric (V) acid.</li>
</ul>
<p><strong>Reason.</strong></p>
<p>&#8211; Dilute nitric (V) acid is a stronger acid hence ionizes fully to yield more hydrogen ions than concentrated nitric (V) acid.</p>
<p>&#8211; Dilute nitric (V) acid is ionic whereas concentrated nitric (V) acid is molecular;</p>
<p>&#8211; Dilute nitric (V) acid is more (highly) ionized than concentrated nitric (V) acid.</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Flow diagram for the otswaldÂs process.</strong></p>
<p><strong> Ammonia</strong></p>
<table>
<tbody>
<tr>
<td width="107"></td>
<td width="126"></td>
<td width="78"></td>
<td width="162"></td>
<td width="78"></td>
<td width="114"></td>
</tr>
<tr>
<td></td>
<td rowspan="3"></td>
</tr>
<tr>
<td></td>
<td></td>
<td rowspan="3" width="162">
<table width="100%">
<tbody>
<tr>
<td><strong>HEAT EXCHANGER</strong></td>
</tr>
</tbody>
</table>
</td>
<td></td>
<td width="114">
<table width="100%">
<tbody>
<tr>
<td><strong>CATALYTIC CHAMBER</strong></td>
</tr>
</tbody>
</table>
</td>
</tr>
<tr>
<td></td>
</tr>
<tr>
<td></td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p> ;</p>
<p><strong>Air</strong></p>
<table>
<tbody>
<tr>
<td width="0"></td>
<td width="2"></td>
<td width="101"></td>
<td width="55"></td>
<td width="154"></td>
<td width="86"></td>
</tr>
<tr>
<td></td>
<td colspan="4"></td>
<td rowspan="2"></td>
</tr>
<tr>
<td></td>
<td colspan="2"></td>
<td rowspan="4"></td>
</tr>
<tr>
<td></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p> ;</p>
<p>Water Unreacted NO<sub>(g)</sub></p>
<p><strong> </strong>NO + air;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p> ;</p>
<p><strong> </strong><strong>Nitric (V) acid</strong></p>
<p><strong> </strong></p>
<p><strong>Pollution effects of nitrogen compounds</strong>.</p>
<ol>
<li><strong> Acid rain</strong></li>
</ol>
<p>&#8211; Nitrogen (II) oxide is produced in internal combustion engines on combination of nitrogen and oxygen.</p>
<p>&#8211; Nitrogen (II) oxide oxidized to nitrogen (IV) oxide which dissolves in water to form nitric (III) and nitric (V) acids.</p>
<p>&#8211; Nitric (v) acid eventually reaches ground as acid rain and causes:</p>
<ul>
<li>Loss of chlorophyll (chlorosis) from leaves</li>
<li>Corrosion of stone buildings and metallic structures, weakening them and destroying beauty.</li>
<li>Leaching of vital minerals from soils. These are converted into soluble nitrates and washed away from top soil. This leads to poor crop yields.</li>
</ul>
<p> ;</p>
<ol start="2">
<li><strong> Smog formation.</strong></li>
</ol>
<p>&#8211; Nitrogen (IV) oxide also undergoes series of chemical reactions in air to produce one of the major components of <strong>smog</strong>.</p>
<p>&#8211; Smog reduces visibility for motorists, irritates eyes and causes breathing problems.</p>
<p> ;</p>
<ol start="3">
<li><strong> Eutrophication:</strong></li>
</ol>
<p>&#8211; Refers to enrichment of water with excess nutrients for algal growth.</p>
<p>&#8211; Presence of nitrate ions from nitrogen fertilizers in a water mass encourages rapid growth of algae.</p>
<p>&#8211; This eventually leads to reduction of dissolved oxygen in water, killing aquatic animals like fish.</p>
<p>&#8211; Presence of <strong>nitrate ions</strong> in <strong>drinking water</strong> may also cause <strong>ill health</strong> to humans. This is because they are converted into carcinogenic compounds.</p>
<p><strong> </strong></p>
<p><strong>Prevention.</strong></p>
<ol>
<li>Recycling unreacted gases in manufacture of nitric acid to prevent release into environment.</li>
<li><strong>Treating sewage</strong> and <strong>industrial effluents</strong> to remove nitrogen compounds before releasing to rivers and lakes.</li>
<li>Fitting exhausts systems of vehicles with <strong>catalytic converters</strong> which convert nitrogen oxides into harmless nitrogen gas.</li>
<li>Adding lime to lakes and soils in surrounding regions to reduce acidity.</li>
<li>Applying fertilizers at right and in the correct proportion to prevent them from being washed into water masses.</li>
</ol>
<p><strong> </strong></p>
<p><strong>UNIT 3: SULPHUR AND ITS COMPOUNDS</strong></p>
<p><strong>Checklist:</strong></p>
<p><strong> </strong></p>
<ol>
<li>Occurrence of sulphur</li>
<li>Extraction of sulphur</li>
</ol>
<ul>
<li>The Frasch pump</li>
<li>Extraction process</li>
</ul>
<ol start="3">
<li>Properties of sulphur</li>
</ol>
<ul>
<li>Physical properties</li>
<li>Chemical properties</li>
</ul>
<ol start="4">
<li>Uses of sulphur</li>
<li>Allotropes of sulphur</li>
</ol>
<ul>
<li>Rhombic sulphur</li>
<li>Monoclinic sulphur</li>
</ul>
<ol start="6">
<li>Compounds of sulphur</li>
</ol>
<ul>
<li>Sulphur (IV) oxide</li>
<li>Laboratory preparation</li>
<li>Other preparation methods</li>
<li>Properties of sulphur (IV) oxide
<ul>
<li>Physical properties</li>
<li>Chemical properties</li>
<li>Uses of sulphur (IV) oxide</li>
</ul>
</li>
</ul>
<ol start="7">
<li>Sulphur (VI) oxide</li>
</ol>
<ul>
<li>Laboratory preparation</li>
<li>Properties of sulphur (VI) oxide</li>
</ul>
<ol start="8">
<li>Sulphuric (VI) acid</li>
</ol>
<ul>
<li>Large scale manufacture
<ul>
<li>Raw materials</li>
<li>The chemical process</li>
<li>Pollution control</li>
</ul>
</li>
<li>Properties of concentrated sulphuric (VI) acid
<ul>
<li>Physical properties</li>
<li>Chemical properties</li>
</ul>
</li>
<li>Properties of dilute sulphuric (VI) acid</li>
<li>Uses of sulphuric (VI) acid</li>
</ul>
<ol start="8">
<li>Hydrogen sulphide gas</li>
</ol>
<ul>
<li>Laboratory preparation</li>
<li>Properties of hydrogen sulphide</li>
<li>Physical properties of hydrogen sulphide</li>
<li>Chemical properties of hydrogen sulphide</li>
</ul>
<ol start="9">
<li>Atmospheric pollution by sulphur compounds</li>
</ol>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong><u> </u></strong></p>
<p><strong>Occurrence</strong></p>
<p>&#8211; Occurs naturally as s free element in the underground deposits in Texas and Louisiana (USA) and Sicily (ITALY).</p>
<p>&#8211; It also occurs as a sulphate and sulphide ores.</p>
<p><strong> </strong></p>
<p><strong>Examples;</strong></p>
<p>Metallic sulphides: iron pyrites (FeS<sub>2</sub>); Zinc blende (ZnS) Copper pyrites (CuFeS<sub>2</sub>)</p>
<p>Metallic sulphates e.g. Gypsum, CaSO<sub>4</sub></p>
<p>Hydrogen sulphide e.g. H<sub>2</sub>S present in natural gas.</p>
<p><strong><u> </u></strong></p>
<p><strong>Extraction of sulphur: The Frasch process</strong></p>
<p>&#8211; Is done using a set of 3 concentric pipes called <strong>Frasch pump</strong>; hence the name <strong>Frasch process</strong>.</p>
<p><strong> </strong></p>
<p><strong>(i). Apparatus</strong>: Frasch pump</p>
<table>
<tbody>
<tr>
<td width="12"></td>
</tr>
<tr>
<td></td>
<td width="208">
<table width="100%">
<tbody>
<tr>
<td>Hot compressed air</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="208">
<table width="100%">
<tbody>
<tr>
<td>Superheated water at 170<sup>o</sup>C</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="208">
<table width="100%">
<tbody>
<tr>
<td>Froth of molten sulphur</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>Cross section of the Frasch pump</strong></p>
<table>
<tbody>
<tr>
<td width="167"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Outermost pipe: brings superheated water at 170<sup>o</sup>C</p>
<table>
<tbody>
<tr>
<td width="184"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p>Innermost pipe: brings in hot compressed air;</p>
<p> ;</p>
<p>Middle pipe: brings out a froth of molten sulphur</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong>(ii). Chemical process</strong></p>
<p><strong>Note: </strong>Sulphur cannot be mined by conventional mining methods such as open cast, alluvial mining etc</p>
<p><strong>Reasons: </strong></p>
<p>&#8211; Sulphur deposits lie <strong>very deep</strong> under several layers of quicksand hence cannot be accessed easily.</p>
<p>&#8211; Sulphur deposits are associated with poisonous gases such as sulphur (IV) oxide gas which can cause massive pollution if exposed to open environment.</p>
<p>&#8211; Three concentric pipes, constituting the <strong>Frasch pump</strong> are drilled through the rock and soil down to the sulphur deposits.</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>(a). The outer tube (pipe)</strong></p>
<p>&#8211; Is used to pump superheated water at 170<sup>o</sup> c and 10 atmospheres down the deposits.</p>
<p>&#8211; The heat of the water melts the sulphur.</p>
<p>&#8211; By the time the water reaches the sulphur, its temperature drops to 120<sup>o</sup>C, but this is enough to melt sulphur whose M.P is 114<sup>o</sup>C.</p>
<p><strong> </strong></p>
<p><strong>(b). The innermost tube</strong></p>
<p>&#8211; Is the smallest pipe and is used to blow or force a jet of hot compressed air down the sulphur deposits.</p>
<p>&#8211; This produces a light froth of molten sulphur (mixture of air, water and sulphur) which is forced up the middle pipe.</p>
<p><strong> </strong></p>
<p><strong>(c). The middle pipe</strong>.</p>
<p>&#8211; Allows the sulphur froth (mixture of molten sulphur, water and air) into the surface; where mixture is run into large tanks.</p>
<p>&#8211; The forth usually settles in two layers, the bottom layer is mainly water while the upper layer is mainly molten sulphur; due to differences in density.</p>
<p>&#8211; Once in the settling tanks, sulphur solidifies and separates out; giving 99% pure sulphur.</p>
<p>&#8211; The sulphur is removed, melted again and poured into moulds, to form roll sulphur in which form it is sold.</p>
<p> ;</p>
<p><strong>Properties of sulphur</strong></p>
<p><strong>Physical properties</strong></p>
<ol>
<li>&#8211; It is a yellow solid which exists in one amorphous form and 2 crystalline forms.</li>
</ol>
<p>&#8211; A molecule of sulphur consists of a pluckered ring of 8 sulphur atoms covalently bonded.</p>
<p><strong> </strong></p>
<p><strong>Diagram: structure of a sulphur molecule.</strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<ol start="2">
<li><strong> Solubility</strong></li>
</ol>
<p>&#8211; It is insoluble in water but soluble in organic solvents like carbon disulphide, xylene and toluene.</p>
<p> ;</p>
<ol start="3">
<li>It is a poor conductor of heat and electricity since it is a covalent element lacking free electrons or ions.</li>
</ol>
<p><strong> </strong></p>
<ol start="4">
<li><strong> Effects of heat</strong></li>
</ol>
<p>&#8211; When sulphur is heated out of contact with air, it melts at low temperatures of about 113<sup>o</sup>C to form an <strong>amber (orange) coloured</strong> mobile liquid.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; The S<sub>8</sub> rings open up to form chains of S<sub>8</sub>.</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Diagrams:</strong></p>
<p><strong>The pluckered S<sub>8</sub> ring of sulphur molecule Chains of S<sub>8</sub> molecule</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p>&#8211; On further heating, the liquid <strong>darkens in colour.</strong></p>
<p>&#8211; At 160<sup>o</sup>C, the liquid becomes <strong>much darker and very viscous</strong> (such that the test tube can be inverted without the sulphur pouring out.)</p>
<p>&#8211; The viscosity continues to increase until a temperature of about 195<sup>0</sup>C</p>
<p><strong>Reason:</strong></p>
<p>&#8211; The S<sub>8</sub> rings of sulphur are <strong>broken</strong> and they then <strong>join</strong> to form <strong>very long chains</strong> of sulphur atoms, with over <strong>100,000 atoms</strong> (S<sub>100 000</sub>).</p>
<p> ;</p>
<p><strong>Note:</strong> As the <strong>chains entangle</strong> with one another the <strong>viscosity increases</strong> and <strong>colour darkens</strong>.</p>
<p> ;</p>
<p>&#8211; Near the <strong>boiling point</strong>, the liquid becomes <strong>less dark</strong> i.e. red-brown and more mobile (runny).</p>
<p><strong>Reason</strong></p>
<p>&#8211; The long chains are broken to shorter chains.</p>
<p> ;</p>
<p>&#8211; At 444<sup>o</sup>C (boiling point), <strong>sulphur vapourises</strong> to form a <strong>red-brown vapour</strong> consisting of S<sub>8</sub>, S<sub>6</sub>, S<sub>4</sub> and S<sub>2</sub> molecules.</p>
<p><strong>Reason</strong></p>
<p>&#8211; The sulphur liquid changes state to form sulphur vapour.</p>
<p>&#8211; The vapour is <strong>light brown</strong> in colour, and consists of a mixture of molecules of formula S<sub>2</sub>-S<sub>10</sub></p>
<p><strong> </strong></p>
<p><strong>Note</strong></p>
<p><strong>&#8211; </strong>If heated further the larger sulphur vapour molecules (S<sub>8</sub>, S<sub>6</sub> etc) dissociate and at 750<sup>o</sup>C the vapour is mostly constituted of diatomic molecules (S<sub>2</sub>)</p>
<p><strong>&#8211; </strong>On exposure to <strong>cold surfaces</strong> the <strong>light brown vapour</strong> condenses to a <strong>yellow sublimate</strong>. The yellow sublimate is called flowers of sulphur.</p>
<p> ;</p>
<p><strong>Chemical properties</strong></p>
<ol>
<li><strong> Burning in air</strong></li>
</ol>
<p>&#8211; It burns in air with a <strong>bright blue flame</strong> forming a misty gas with a choking smell.</p>
<p>&#8211; The gas is sulphur (IV) oxide, with traces of sulphur (VI) oxide, both of which are acidic.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>S<sub>(s)</sub> + O<sub>2(g)</sub> SO<sub>2(g)</sub></p>
<p><strong> </strong></p>
<p><strong>Note:</strong></p>
<p>The SO<sub>3</sub> is formed due to further oxidation of some of the SO<sub>2</sub> gas</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2SO<sub>2(s)</sub> + O<sub>2(g)</sub> 2SO<sub>3(g)</sub></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<ol start="2">
<li><strong> Reaction with acids.</strong></li>
</ol>
<p>&#8211; Dilute acids have no effect on sulphur.</p>
<p>&#8211; It is however easily oxidized by concentrated (VI) sulphuric acid and Nitric (VI) acid.</p>
<p><strong> </strong></p>
<ul>
<li><strong>With conc. H<sub>2</sub>SO<sub>4</sub></strong></li>
</ul>
<p>&#8211; When warmed with conc. H<sub>2</sub>SO<sub>4</sub>, sulphur is oxidized to sulphur (IV) oxide while the acid is reduced to the same gas.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>S<sub>(s)</sub> + 2H<sub>2</sub>SO<sub>4(l)</sub> 3SO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong> </strong></p>
<ul>
<li><strong>With conc. HNO<sub>3</sub></strong></li>
</ul>
<p>&#8211; Sulphur is oxidized to sulphuric (VI) acid while acid itself is reduced to red-brown Nitrogen (IV) oxide.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>S<sub>(s)</sub> + 6HNO<sub>3(l)</sub> H<sub>2</sub>SO<sub>4(aq)</sub> + 6NO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong> </strong></p>
<p><strong>Note:</strong></p>
<p>&#8211; The resultant solution gives a white precipitate with a solution of Barium chloride.</p>
<p><strong>Reason</strong></p>
<p>&#8211; Due to presence of sulphate ions which combine with Ba<sup>2+</sup> to form insoluble BaSO<sub>4(s)</sub></p>
<p><strong> </strong></p>
<p><strong>Ionically;</strong></p>
<p>Ba<sup>2+</sup><sub>(aq) </sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> BaSO<sub>4(s)</sub></p>
<p><strong> </strong></p>
<ol start="3">
<li><strong> Reaction with other elements.</strong></li>
</ol>
<p>&#8211; It combines directly with many other elements to form sulphides.</p>
<p>&#8211; With metals, sulphur forms metal sulphides, most of which are black.</p>
<p><strong> </strong></p>
<p><strong>Examples.</strong></p>
<p><strong>(a). With metals</strong></p>
<p><strong> </strong></p>
<ul>
<li><strong>Iron metal</strong></li>
</ul>
<p>Fe<sub>(s)</sub> + S<sub>(s)</sub> FeS<sub>(s)</sub> + Heat</p>
<p><strong><em>(Grey) (Yellow) (Black)</em></strong></p>
<p><strong> </strong></p>
<p><strong>Note</strong>:</p>
<p>&#8211; During the reaction, the mixture glows spontaneously; immediately the reaction has started.</p>
<p><strong> </strong></p>
<ul>
<li><strong>Copper</strong></li>
</ul>
<p>2Cu<sub>(s)</sub> + S<sub>(s)</sub> Cu<sub>2</sub>S</p>
<p><strong><em>(Red-brown) (Yellow) (Black copper (I) sulphide))</em></strong></p>
<p><strong> </strong></p>
<p><strong>(b). Non-metals</strong></p>
<p><strong> </strong></p>
<ul>
<li><strong>Carbon</strong></li>
</ul>
<p>C<sub>(s)</sub> + 2S<sub>(s)</sub> CS<sub>2</sub>(s)</p>
<p><strong><em>(Black) (Yellow) (Black Carbon disulphide)</em></strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Note</strong>.</p>
<p>&#8211; Carbon (IV) sulphide has a distinct smell.</p>
<p>&#8211; It is an excellent solvent and is used as a <strong>pesticide</strong> due to its poisonous nature.</p>
<p><strong> </strong></p>
<ul>
<li><strong>Hydrogen</strong></li>
</ul>
<p>H<sub>2(g)</sub> + S<sub>(s)</sub> H<sub>2</sub>S<sub>(g)</sub></p>
<p><strong> </strong></p>
<ul>
<li><strong>Fluorine</strong></li>
</ul>
<p>S<sub>(s)</sub> + F<sub>2(g)</sub> SF<sub>2(g)</sub></p>
<p><strong> </strong></p>
<ul>
<li><strong>Chlorine</strong></li>
</ul>
<p>S<sub>(s)</sub> + Cl<sub>2(g)</sub> SCl<sub>2(g)</sub></p>
<p><strong> </strong></p>
<ul>
<li><strong>Bromine</strong></li>
</ul>
<p>2S<sub>(s)</sub> +Br<sub>2(g)</sub> S<sub>2</sub>Br<sub>2(g)</sub></p>
<p><strong> </strong></p>
<ul>
<li><strong>Phosphorous</strong></li>
</ul>
<p>10S<sub>(s)</sub> + 4P<sub>(s)</sub> P<sub>4</sub>S<sub>10(s)</sub></p>
<p><strong> </strong></p>
<p><strong>Note: </strong></p>
<p>&#8211; Sulphur does not react with inert gases, nitrogen and iodine.</p>
<p><strong> </strong></p>
<p><strong>Uses of sulphur</strong></p>
<ol>
<li>Industrial manufacture of sulphuric (VI) acid in the contact process.</li>
<li>It is used as a <strong>fungicide </strong>for treatment of fungal <strong>skin diseases</strong>.</li>
<li>It is used for <strong>vulcanization</strong> (hardening) of rubber</li>
<li>Manufacture of <strong>calcium hydrogen sulphite</strong> (Ca(HSO<sub>3</sub>)<sub>2</sub> used for bleaching in paper and textile industries.</li>
<li>Manufacture of <strong>matches</strong> and <strong>fireworks.</strong></li>
<li>Manufacture of <strong>dyes</strong> e.g. sulphur blacks that gives paint smooth texture.</li>
<li>Manufacture of sulphur <strong>ointments</strong> and <strong>drugs</strong> e.g. sulphur-guanidine for dysentery.</li>
<li>Manufacture of <strong>hair oil.</strong></li>
<li>Small amounts of sulphur are added to <strong>concrete</strong> to prevent <strong>corrosion by acids.</strong></li>
<li>Manufacture of fungicides for spraying crops against fungal infections e.g. ridomil, dithane for potato and tomato blights</li>
</ol>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Allotropes of sulphur</strong></p>
<p>&#8211; Allotropy is the existence of an element in more than one form without change of state.</p>
<p>&#8211; Sulphur has 2 allotropes</p>
<ul>
<li>Rhombic sulphur/ octahedral/ alpha-sulphur</li>
<li>Monoclinic/ prismatic sulphur/ beta-sulphur.</li>
</ul>
<p> ;</p>
<p>-Unlike carbon only the rhombic sulphur occurs naturally.</p>
<p> ;</p>
<p><strong>Comparison of rhombic and monoclinic sulphur.</strong></p>
<p><strong> </strong></p>
<table>
<tbody>
<tr>
<td width="237"><strong> Allotrope </strong></p>
<p><strong>Characteristic</strong></td>
<td width="294"><strong>Rhombic sulphur</strong></td>
<td width="294"><strong>Monoclinic sulphur</strong></td>
</tr>
<tr>
<td width="237">Stability</td>
<td width="294">&#8211; Stable below transitional temp. of 96<sup>o</sup>C</td>
<td width="294">&#8211; Stable above 96<sup>o</sup>C</td>
</tr>
<tr>
<td width="237">Colour</td>
<td width="294">&#8211; Bright yellow crystalline solid</td>
<td width="294">&#8211; Pale yellow crystalline solid</td>
</tr>
<tr>
<td width="237">Melting point</td>
<td width="294">&#8211; Melts at 113<sup>o</sup>C;</td>
<td width="294">&#8211; Melts at 119<sup>o</sup>C;</td>
</tr>
<tr>
<td width="237">Density</td>
<td width="294">&#8211; About 2.06gcm<sup>-3</sup>(heavier than monoclinic Sulphur)</td>
<td width="294">&#8211; Lighter than 1.98gcm<sup>-3</sup> (lighter than rhombic sulphur)</td>
</tr>
<tr>
<td width="237">Shape</td>
<td width="294">&#8211; Octahedral shape</p>
<p><strong>Diagram:</strong></p>
<p> ;</td>
<td width="294">&#8211; Needle-like/ prismatic</p>
<p><strong>Diagram:</strong></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>Note.</strong></p>
<p>96<sup>o</sup>C is called transitional temperature; because both allotropes are stable.</p>
<p><strong><u> </u></strong></p>
<p><strong>Compounds of sulphur</strong></p>
<p><strong> </strong></p>
<p><strong>Oxides of sulphur.</strong></p>
<p><strong> </strong></p>
<p><strong>Sulphur (IV) oxide</strong></p>
<p><strong>Laboratory preparation of sulphur (IV) oxide</strong></p>
<p><strong>(i). Apparatus:</strong></p>
<table>
<tbody>
<tr>
<td width="172">
<table width="100%">
<tbody>
<tr>
<td>Dry sulphur (IV) oxide gas</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="112">
<table width="100%">
<tbody>
<tr>
<td>Sodium sulphite</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="100">
<table width="100%">
<tbody>
<tr>
<td>Dilute HCl</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="112">
<table width="100%">
<tbody>
<tr>
<td>Conc. H<sub>2</sub>SO<sub>4(l)</sub></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure</strong></p>
<p>&#8211; Dilute HCl or H<sub>2</sub>SO<sub>4</sub> is poured into sodium sulphite crystals in the flask.</p>
<p>&#8211; The gas produced is passed through conc. Sulphuric acid to dry it.</p>
<p>&#8211; If the reaction is slow, the round-bottomed flask is heated (warmed) gently.</p>
<p>&#8211; Dry gas is collected by <strong>downward delivery</strong> as it is denser than air.</p>
<p><strong> </strong></p>
<p><strong>(ii). Equation</strong>.</p>
<p>Na<sub>2</sub>SO<sub>3(aq)</sub> + 2HCl<sub>(aq)</sub> H<sub>2</sub>O<sub>(l)</sub> + SO<sub>2(g)</sub> + 2NaCl<sub>(aq)</sub></p>
<p><strong> </strong></p>
<p><strong>Ionically;</strong></p>
<p>2H<sup>+</sup><sub>(aq)</sub> + SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> H<sub>2</sub>O<sub>(l)</sub> + SO<sub>2(g)</sub></p>
<p><strong> </strong></p>
<p><strong>Note</strong>:</p>
<p>&#8211; Nitric (V) acid should not be used.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; It is a strong oxidizing agent and cannot therefore reduce the metal sulphites.</p>
<p>&#8211; Instead it will oxidize the SO<sub>2</sub> produced to sulphuric (VI) acid</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2HNO<sub>3(aq)</sub> + SO<sub>2(g)</sub> 2NO<sub>2(g)</sub> + H<sub>2</sub>SO<sub>4(l)</sub></p>
<p> ;</p>
<p><strong>Other methods of preparing sulphur (IV) oxide.</strong></p>
<p><strong>(b). Preparation from concentrated sulphuric (VI) acid</strong></p>
<p><strong>(i). Apparatus</strong></p>
<p>&#8211; As in (a) above</p>
<p><strong> </strong></p>
<p><strong>(ii). Procedure</strong></p>
<p>&#8211; Copper turnings are covered with concentrated sulphuric (VI) acid and the mixture <strong>heated </strong>(a must in this case).</p>
<p><strong>Note:</strong></p>
<p>&#8211; Dilute sulphuric (VI) acid does not react with copper hence the need for concentrated acid.</p>
<p>&#8211; Cold concentrated sulphuric (VI) acid does not also react with copper hence warming.</p>
<p> ;</p>
<p><strong>(iii). Observation</strong>.</p>
<p>&#8211; When the solution becomes hot, there is evolution of sulphur (IV) oxide gas.</p>
<p><strong> </strong></p>
<p><strong>Equation.</strong></p>
<p>C<sub>u(s)</sub> +2H<sub>2</sub>SO<sub>4(l)</sub> CuSO<sub>4(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + SO<sub>2(g)</sub></p>
<p><strong> </strong></p>
<p><strong>Note:</strong></p>
<p>&#8211; This reaction is in two stages.</p>
<ul>
<li><strong>Oxidation of Cu to CuO</strong></li>
</ul>
<p>&#8211; Concentrated sulphuric (VI) acid oxidizes copper to Copper (II) oxide</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Cu<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(l)</sub> CuO<sub>(s)</sub> + H<sub>2</sub>O<sub>(l)</sub> + SO<sub>2(g)</sub></p>
<p> ;</p>
<ul>
<li><strong>CuO further reacts with the acid to form salt and water.</strong></li>
</ul>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>CuO<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(l)</sub> CuSO<sub>4(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Overall equation:</strong></p>
<p>Cu<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(l)</sub> CuSO<sub>4(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + SO<sub>2(g)</sub></p>
<p><strong> </strong></p>
<p><strong>(c). Roasting sulphur in air</strong></p>
<p>&#8211; When sulphur is burnt in air, SO<sub>2</sub> is produced.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>S<sub>(s)</sub> + O<sub>2(g)</sub> SO<sub>2(g)</sub></p>
<p><strong> </strong></p>
<p><strong>Note:</strong></p>
<p>This reaction is not suitable for preparing a pure sample of the gas in the lab.</p>
<p><strong>Reason </strong></p>
<p>&#8211; The gas is contaminated with traces of O<sub>2</sub>; N<sub>2</sub>; CO<sub>2</sub> and inert gases.</p>
<p>&#8211; There are higher chances of environmental pollution, due to escape of some of the gas into the atmosphere.</p>
<p> ;</p>
<p><strong>(d). Roasting metal sulphides in air</strong></p>
<p><strong>Examples:</strong></p>
<p>2FeS<sub>(g)</sub> + 3O<sub>2(g)</sub> 2FeO<sub>(s)</sub> + 2SO<sub>2(g)</sub></p>
<p>2ZnS<sub>(g)</sub> + 3O<sub>2(g)</sub> 2ZnO<sub>(s)</sub> + 2SO<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Preparation of sulphur (IV) oxide solution.</strong></p>
<p><strong>(i). Apparatus</strong></p>
<p><strong> </strong></p>
<p><strong>(ii). Procedure</strong></p>
<p>&#8211; Gas is directly passed into water using an <strong>inverted funnel</strong>; to prevent “<strong>sucking back</strong>” by increasing surface area for dissolution.</p>
<p> ;</p>
<p><strong>Properties of sulphur (IV) oxide gas</strong></p>
<p><strong>Physical properties</strong></p>
<ol>
<li>It is a colourless gas with an irritating (pungent) characteristic smell.</li>
<li>It neither burns nor supports combustion i.e. when a lighted splint is introduced into a gas jar full of sulphur (IV) oxide, the splint is extinguished.</li>
<li>It has a low PH.</li>
</ol>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Chemical properties.</strong></p>
<p>&#8211; It is a strong reducing agent.</p>
<p>&#8211; An aqueous solution of sulphur (IV) oxide, sulphurous acid is strong reducing agent.</p>
<p>&#8211; The sulphite radical, SO<sub>3</sub><sup>2-</sup>, acts as a supplier of electrons; the overall reaction results into formation of sulphate ions.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>H<sub>2</sub>SO<sub>3(aq)</sub> 2H<sup>+</sup><sub>(aq)</sub> + SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> then;</p>
<p> ;</p>
<p>SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + 2H<sup>+</sup><sub>(aq)</sub> + 2e-</p>
<p> ;</p>
<p>&#8211; The resultant electrons supplied are accepted by an oxidizing agent, which consequently gets reduced.</p>
<p> ;</p>
<p><strong>Examples: </strong></p>
<p><strong>(i). Reduction of acidified potassium manganate (VII).</strong></p>
<p><strong>Procedure.</strong></p>
<p>-To about 2 cm<sup>3</sup> of sulphur (IV) oxide solution, 2 cm<sup>3</sup> of dilute H<sub>2</sub>SO<sub>4 </sub>was added followed by an equal volume of potassium manganate (VII) solution.</p>
<p> ;</p>
<p><strong>Observations</strong></p>
<p>&#8211; Purple solution changes to colourless.</p>
<p> ;</p>
<p><strong>Explanation</strong></p>
<p>&#8211; Purple manganate (VII) ions are reduced to colourless manganate (II) ions, while H<sub>2</sub>SO<sub>3</sub> (sulphurous (IV) acid) is reduced to sulphate ions and water.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p><strong> </strong></p>
<p>5SO<sub>2(g)</sub> + 2KMnO<sub>4(aq)</sub> + 2H<sub>2</sub>O K<sub>2</sub>SO<sub>4(aq)</sub> + 2MnSO<sub>4(aq)</sub>+ H<sub>2</sub>SO<sub>4(aq)</sub></p>
<p> ;</p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>2MnO<sup>&#8211;</sup><sub>4(aq)</sub> + 5SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> + 6H<sup>+</sup><sub>(aq)</sub> 2Mn<sup>2+</sup><sub>(aq)</sub> + 5SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + 3H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>(ii). Reduction of potassium chromate (IV) solution </strong></p>
<p><strong> </strong></p>
<h1>Procedure</h1>
<p>&#8211; To 2 cm<sup>3 </sup>of Sulphur (IV) oxide solution, 2 cm<sup>3</sup> of dilute H<sub>2</sub>SO<sub>4</sub> was added followed by an equivalent volume of potassium chromate (VI) solution.</p>
<p> ;</p>
<h1>Observation</h1>
<p>&#8211; Acidified potassium chromate (VI) solution change from <strong>orange</strong> to <strong>green</strong>.</p>
<p> ;</p>
<p><strong>Equation</strong></p>
<p>K<sub>2</sub>Cr<sub>2</sub>O<sub>7(aq)</sub> + 3SO<sub>2(aq)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> K<sub>2</sub>SO<sub>4(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + Cr<sub>2</sub>(SO<sub>4</sub>)<sub>3(aq)</sub></p>
<p><strong><em>(Orange) (Green)</em></strong></p>
<p><strong> </strong></p>
<p><strong>Ionically: </strong><strong><em>Oxidation</em></strong></p>
<table>
<tbody>
<tr>
<td width="95"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p> ;</p>
<p>Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup><sub>(aq) </sub>+ 3SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> + 8H<sup>+</sup><sub>(aq)</sub> 2Cr<sup>3+</sup><sub>(aq)</sub> + 3SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub></p>
<table>
<tbody>
<tr>
<td width="35"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p> ;</p>
<p><strong><em>Reduction</em></strong></p>
<p><strong>Note:</strong> this is the usual <strong>chemical test</strong> for sulphur (IV) oxide.</p>
<p> ;</p>
<p><strong>(iii). Reduction of Iron (III) ions to Iron (II) ions (Fe<sup>3+</sup> to Fe<sup>2+</sup>)</strong></p>
<p> ;</p>
<h1>Procedure</h1>
<p>&#8211; About 3 cm<sup>3</sup> of Iron (III) chloride solution are heated in a test tube and sulphur (IV) oxide gas bubbled into it.</p>
<p> ;</p>
<h1>Observations</h1>
<p>&#8211; The <strong>brown</strong> solution turns <strong>green</strong>.</p>
<p> ;</p>
<h1>Explanation</h1>
<p>&#8211; Aqueous sulphur (IV) oxide reduces to Fe<sup>3+</sup> in FeCl<sub>3</sub> which are brown to green Fe<sup>2+</sup> in FeCl<sub>2(aq)</sub>.</p>
<p> ;</p>
<h2>Ionically</h2>
<p>2Fe<sup>3+</sup><sub>(aq)</sub> + SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l) </sub> Fe<sup>2+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> + H<sup>+</sup><sub>(aq)</sub></p>
<p> ;</p>
<p> ;</p>
<p><strong>(iv). Reduction of bromine water</strong></p>
<p> ;</p>
<h1>Procedure</h1>
<p>&#8211; Bromine water (red brown) is added to a solution of sulphur (IV) oxide followed by HCl and BaCl<sub>2 </sub>solution.</p>
<p> ;</p>
<p><strong>Equation</strong></p>
<p>Br<sub>2(aq)</sub> + SO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> 2HBr<sub>(aq)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub></p>
<p><strong> </strong></p>
<p><strong>Ionically:</strong><strong> <em><sup>Oxidation</sup></em></strong></p>
<table>
<tbody>
<tr>
<td width="0"></td>
<td width="2"></td>
<td width="197"></td>
<td width="12"></td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td rowspan="2"></td>
</tr>
<tr>
<td></td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p> ;</p>
<p>Br<sub>2(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> 2HBr<sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub></p>
<p><strong><em>(Red-brown) (Colourless)</em></strong></p>
<table>
<tbody>
<tr>
<td width="47"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<h2><em>Reduction</em></h2>
<h2></h2>
<h2>On addition of barium chloride</h2>
<p>&#8211; A <strong>white precipitate</strong> is formed, due to the formation of insoluble <strong>barium sulphate.</strong></p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Ba<sup>2+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> BaSO<sub>4(s)</sub></p>
<h1></h1>
<h1>Note</h1>
<p>&#8211; This test confirms presence of SO<sub>4</sub><sup>2-</sup> since a white precipitate insoluble in dilute hydrochloric acid is formed.</p>
<p>&#8211; CO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> and SO<sub>3</sub><sup>2-</sup> also forms a white precipitate with BaCl<sub>2(aq)</sub> but the white precipitates dissolve in dilute HCl<sub>(aq)</sub></p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>(v). Reduction of hydrogen peroxide</strong></p>
<p><strong> </strong></p>
<p><strong>Procedure</strong></p>
<p>&#8211; To 2 cm<sup>3</sup> of aqueous sulphur (IV) oxide, an equal volume of hydrogen peroxide is added followed by 1 cm<sup>3 </sup>of HCl, then a few drops BaCl<sub>2</sub> solution.</p>
<p> ;</p>
<h2>Observation and explanations:</h2>
<p>&#8211; Bubbles of a colourless gas; that relights a glowing splint.</p>
<p>&#8211; Hydrogen peroxide is reduced to water; while the sulphite ion in aqueous sulphur (IV) oxide (H<sub>2</sub>SO<sub>3(aq)</sub>) is oxidized to SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub></p>
<p> ;</p>
<h1>Equation</h1>
<p>H<sub>2</sub>O<sub>2(l)</sub> +SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> H<sub>2</sub>O<sub>(l)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; On addition of BaCl<sub>2</sub>, a white precipitate insoluble in dilute HCl.</p>
<p>&#8211; This confirms presence of sulphate ions.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Ba<sup>2+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> BaSO<sub>4(s)</sub></p>
<p> ;</p>
<p><strong>(vi). Reduction of concentrated nitric (V) acid</strong></p>
<p> ;</p>
<h1>Procedure</h1>
<p>&#8211; Sulphur (IV) oxide is bubbled through (into) a solution of concentrated nitric (v) acid.</p>
<p> ;</p>
<p><strong>Observation </strong></p>
<p>&#8211; Brown fumes (of NO<sub>2</sub>) are liberated.</p>
<p> ;</p>
<p><strong>Explanation</strong></p>
<p>&#8211; Sulphur (IV) oxide reduces nitric (V) acid to nitrogen (IV) oxide (brown) while it is itself oxidized by HNO<sub>3</sub> to form H<sub>2</sub>SO<sub>4</sub>.</p>
<p>&#8211; Thus while SO<sub>2</sub> is the reducing agent; HNO<sub>3</sub> is the oxidizing agent.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2HNO<sub>3(l)</sub> + SO<sub>2(g)</sub> 2NO<sub>2(g)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub></p>
<p><strong><em> (Brown fumes)</em></strong></p>
<p> ;</p>
<p><strong>(vii). Reaction with atmospheric oxygen in light.</strong></p>
<p><strong> </strong></p>
<h1>Procedure:</h1>
<p>&#8211; About 2 cm<sup>3</sup> of Sulphur (IV) oxide solution is left in a test tube in light for 24 hours, dilute HCl is then added, followed by barium chloride.</p>
<p> ;</p>
<h1>Observations and explanations:</h1>
<p>&#8211; Atmospheric oxygen in light oxidizes sulphite ion (SO<sub>3</sub><sup>2-</sup>) into sulphate (SO<sub>4</sub><sup>2-</sup>)</p>
<p> ;</p>
<h1>Equation:</h1>
<p>2SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> + O<sub>2(g)</sub> 2SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; On adding barium chloride, a <strong>white precipitate</strong> insoluble in dilute HCl results; confirming presence of sulphate ion.</p>
<p><strong>Equation:</strong></p>
<p>Ba<sup>2+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> BaSO4<sub>(s)</sub></p>
<p><strong> </strong><strong><em>(White ppt)</em></strong></p>
<p><strong> </strong></p>
<ol start="6">
<li><strong> Sulphur (IV) oxide as oxidizing agent</strong></li>
</ol>
<p>&#8211; It reacts as an oxidizing agent with reducing agents more powerful than itself.</p>
<p> ;</p>
<h1>Examples</h1>
<p><strong> </strong></p>
<p><strong>(a). Reaction with hydrogen sulphide</strong></p>
<p> ;</p>
<h1>Procedure</h1>
<p>&#8211; A test tube of dry hydrogen sulphide gas is inverted into a gas jar full of <strong>moist</strong> sulphur (IV) oxide, and the gases allowed to mix.</p>
<p> ;</p>
<h1>Observation</h1>
<p>&#8211; <strong>Yellow</strong> deposits of sulphur is produced.</p>
<p> ;</p>
<p><strong>Examples: </strong></p>
<p><strong> </strong><strong><em>Oxidation</em></strong></p>
<table>
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</tbody>
</table>
<p><strong> </strong></p>
<p> ;</p>
<p>2H<sub>2</sub>S<sub>(g)</sub> + SO<sub>2(g)</sub> 2H<sub>2</sub>O<sub>(l)</sub> + 3S<sub>(s)</sub></p>
<table>
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<p> ;</p>
<p> ;</p>
<p><strong><em> Reduction</em></strong></p>
<p><strong>Explanations:</strong></p>
<p>&#8211; H<sub>2</sub>S is a <strong>stronger reducing</strong> agent than sulphur (IV) oxide.</p>
<p>&#8211; Thus sulphur (IV) oxide acts as an <strong>oxidizing agent</strong> supplying oxygen to the hydrogen sulphide.</p>
<p> ;</p>
<h1>Note</h1>
<p>&#8211; Dry gases do not react and for this reaction to occur, the gases must be <strong>moist</strong> or at least one of them.</p>
<p> ;</p>
<p><strong>(b). Reaction with burning magnesium</strong></p>
<p><strong> </strong></p>
<p><strong>Procedure</strong></p>
<p>&#8211; Burning magnesium is lowered into a gas jar full of sulphur (IV) oxide.</p>
<p> ;</p>
<p><strong>Observation</strong></p>
<p>&#8211; <strong>White fumes</strong> of magnesium oxide and <strong>yellow specks</strong> of sulphur.</p>
<p> ;</p>
<p><strong>Equation</strong></p>
<p><strong> </strong></p>
<p>2Mg<sub>(s)</sub> + SO<sub>2(g)</sub> 2MgO<sub>(s)</sub> + S<sub>(s)</sub></p>
<p> ;</p>
<ol start="7">
<li><strong> Sulphur (IV) oxide as bleaching agent.</strong></li>
</ol>
<p> ;</p>
<h1>Procedure</h1>
<p>&#8211; Coloured flower petals are placed in a test-tube full of sulphur (IV) oxide.</p>
<p> ;</p>
<h1>Observation</h1>
<p>&#8211; The coloured (blue or red) petals are bleached (turned colorless);</p>
<p> ;</p>
<h1>Explanations:</h1>
<p>&#8211; In presence of water, sulphur (IV) oxide acts as a bleaching agent. It bleaches by reduction (removal of oxygen form the dye)</p>
<p>&#8211; It first combines with water forming the sulphurous acid; which then <strong>reduces</strong> the dye to form a colourless product.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>SO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> H<sub>2</sub>SO<sub>3(aq)</sub></p>
<p> ;</p>
<p>H<sub>2</sub>SO<sub>3(aq) </sub> 2H<sup>+</sup><sub>(aq)</sub> + SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub></p>
<p><strong> </strong></p>
<p>Then;</p>
<p>SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> + [O] SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub></p>
<p><strong> </strong><strong><em>From dye</em></strong></p>
<p><strong> </strong></p>
<p><strong>General equation</strong></p>
<p>SO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> + [Dye + (O)] Dye + H<sub>2</sub>SO<sub>4(aq)</sub></p>
<p><strong><em> Coloured Colourless</em></strong></p>
<h1></h1>
<h1>Note</h1>
<p>&#8211; The original colour may be restored by <strong>oxidation</strong> or prolonged exposure to air. This explains why old newspapers which were originally bleached white by sulphur (IV) oxide turn brown with time.</p>
<p>&#8211; Chlorine bleaches by oxidation hence its oxidation is <strong>permanent</strong>; SO<sub>2</sub> is however preferred because it is milder in action.</p>
<p> ;</p>
<ol start="8">
<li><strong> Reaction with sodium hydroxide (alkalis)</strong></li>
</ol>
<p><strong> </strong></p>
<p><strong>Procedure</strong></p>
<p>&#8211; A gas jar full of sulphur (IV) oxide is inverted over sodium hydroxide solution in a trough and shaken.</p>
<h3>Observations</h3>
<p>&#8211; Solution seen <strong>rises up</strong> in the jar.</p>
<p> ;</p>
<h3>Explanation</h3>
<p>&#8211; Sulphur (IV) oxide is acidic, hence easily absorbed by alkaline solutions such as sodium hydroxide solution.</p>
<p>&#8211; Sodium sulphite and sodium hydrogen sulphites are formed depending on amount of sulphur oxide.</p>
<p> ;</p>
<h2>Equations</h2>
<ul>
<li><strong>With limited sulphur (IV) oxide:</strong></li>
</ul>
<p><strong> </strong></p>
<p>2NaOH<sub>(aq)</sub> + SO<sub>2(g)</sub> Na<sub>2</sub>SO<sub>3(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<ul>
<li><strong>With excess sulphur (IV) oxide:</strong></li>
</ul>
<p><strong> </strong></p>
<p>NaOH<sub>(aq)</sub> + SO<sub>2(g)</sub> NaHSO<sub>3(aq)</sub></p>
<p> ;</p>
<h1>Reaction with chlorine:</h1>
<h1>&#8211; Sulphur (IV) oxide reacts with moist chlorine to form an acidic mixture of sulphuric (VI) acid and hydrochloric acid.</h1>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>SO<sub>2(g)</sub> + SO<sub>2(g)</sub> H<sub>2</sub>O<sub>(l) </sub> H<sub>2</sub>SO<sub>4(aq)</sub> + 2HCl<sub>(aq)</sub></p>
<h1></h1>
<h1>Explanation:</h1>
<p>&#8211; Sulphur (IV) oxide serves as the reducing agent reducing chlorine into hydrochloric acid;</p>
<p>&#8211; Chlorine acts as the oxidizing agent; oxidizing the sulphur (IV) oxide into sulphuric (VI) acid</p>
<p> ;</p>
<h1>Tests for sulphur (iv) oxide</h1>
<ol>
<li>Characteristic pungent smell.</li>
<li>Bleaches flower petals.</li>
<li>Decolourises purple potassium manganate (VII)</li>
<li>Turns filter paper soaked in acidified orange potassium dichromate (VI) solution to green</li>
</ol>
<p> ;</p>
<h1>Sulphur (IV) oxide as a pollutant</h1>
<p>&#8211; It is industrial waste in some chemical processes.</p>
<p>&#8211; The emission to the air it dissolves forming sulphurous acid.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>SO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l) </sub> H<sub>2</sub>SO<sub>3(aq)</sub></p>
<p> ;</p>
<p>&#8211; Sulphurous acid is readily oxidized to sulphuric (VI) acid; which attacks stonework and metal structures causing them to corrode.</p>
<p>&#8211; If breathed in, SO<sub>2</sub> causes lung damage.</p>
<p> ;</p>
<h1>Uses of sulphur (VI) oxide</h1>
<p>&#8211; Industrial manufacture of sulphuric (VI) acid.</p>
<p>&#8211; Fumigation in green houses for purposes of pest and disease control.</p>
<p>&#8211; Preservative in jam and fruit juices.</p>
<p>&#8211; Bleaching agent for wool, straw, paper pulp etc.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong><u> </u></strong></p>
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<p><strong>Sulphuric (VI) acid</strong></p>
<p><strong> </strong></p>
<p><strong>Industrial manufacture of sulphuric (VI) acid: The contact process</strong></p>
<p> ;</p>
<h2>Raw materials</h2>
<p>&#8211; Sulphide ores or sulphur.</p>
<p>&#8211; Water</p>
<p>&#8211; Oxygen (air)</p>
<p>&#8211; Concentrated sulphuric (VI) acid.</p>
<p> ;</p>
<h1>The chemical process</h1>
<p> ;</p>
<h1>Step 1: Production of sulphur (VI) oxide</h1>
<p>&#8211; Sulphur (IV) oxide is obtained b burning the metal ores of sulphides or elemental sulphur in air.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p><strong> </strong></p>
<p>S<sub>(s) </sub>+ O<sub>2(g)</sub> SO<sub>2(g)</sub></p>
<p> ;</p>
<p>&#8211; Obtaining sulphur (IV) oxide form pyrites is <strong>cheaper</strong> than form sulphur.</p>
<p>&#8211; Flowers of sulphur form pyrites is <strong>impure</strong> and contains dust; which involves extra expenses and time in purification.</p>
<p> ;</p>
<p> ;</p>
<h1>Step 2: Purification and drying</h1>
<p>&#8211; The Sulphur (IV) oxide and excess air are passed through a series of <strong>driers</strong> and <strong>purifiers</strong>.</p>
<p>&#8211; Purifiers remove dust particles, which would otherwise <strong>poison</strong> the catalyst used in this process by taking up the catalytic surface thus impairing the catalytic efficiency.</p>
<p>&#8211; Purification (removal of dust) is by <strong>electrostatic precipitation</strong>.</p>
<p>&#8211; Are dried through concentrated sulphuric acid then passed through heat exchanger.</p>
<p> ;</p>
<h1>Step 3: Heat exchanger reactions</h1>
<p>&#8211; The pure dry SO<sub>2</sub> and excess air mixture are passed into heat exchanger reactions.</p>
<p> ;</p>
<p><strong>Reason:</strong></p>
<p>&#8211; To <strong>lower </strong>their temperatures since reaction in the proceeding chamber (catalytic chamber) are <strong>exothermic</strong> hence requiring lower temperatures.</p>
<p> ;</p>
<h2>Step 4: Catalytic chamber</h2>
<p>&#8211; Dry dust-free SO<sub>2</sub> is mixed with clean excess air, heated and passed into a catalytic chamber containing <strong>vanadium (V) oxide catalyst</strong>.</p>
<p> ;</p>
<h1>Equation V<sub>2</sub>O<sub>5</sub></h1>
<p>2SO<sub>2(g)</sub> + O<sub>2(g)</sub> 2SO<sub>3(g)</sub> + Heat</p>
<p><strong>450<sup>o</sup>C</strong></p>
<p> ;</p>
<p>&#8211; The product is <strong>sulphur (VI) oxide</strong>, SO<sub>3</sub>.</p>
<p>&#8211; Formation of sulphur (VI) oxide is accompanied by evolution of heat (<strong>exothermic reaction</strong>) and a reduction in volume.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; A good yield of SO<sub>3</sub> is favoured by the following conditions.</p>
<p> ;</p>
<ol>
<li><strong> Temperature</strong></li>
</ol>
<p>&#8211; The forward reaction is <strong>exothermic</strong> hence the yield can be favourable in <strong>low temperatures</strong>.</p>
<p>&#8211; However, at such low temperatures the equilibrium is attained very slowly.</p>
<p>&#8211; At high temperatures, equilibrium is achieved very quickly but sulphur (VI) oxide decomposes considerably.</p>
<p>&#8211; Thus a compromise optimum temperature of about 450<sup>o</sup>C is used in order to enable as much sulphur (VI) oxide as possible to be made in a reasonable time.</p>
<p>&#8211; From the graph, high SO<sub>3</sub> yield is favoured by relatively low temperatures.</p>
<p><strong> </strong></p>
<p><strong>Graph: %age yield of sulphur (VI) oxide against temperature.</strong></p>
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<ol start="2">
<li><strong> Pressure</strong></li>
</ol>
<p>&#8211; High pressures favour production of more sulphur (VI) oxide.</p>
<p> ;</p>
<h1>Reason</h1>
<p>&#8211; The volume of <strong>gaseous reactants</strong> is higher than volume of <strong>gaseous products</strong>.</p>
<p>&#8211; Since reaction involves reduction in volume, theoretically pressure used should be as high as is economically convenient.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; High pressures are however disadvantageous.</p>
<p> ;</p>
<h1>Reason</h1>
<p>&#8211; The equipment required to generate high pressure would be expensive to maintain.</p>
<p>&#8211; The high pressure could also liquefy sulphur (VI) oxide.</p>
<p>&#8211; A pressure slightly above atmospheric pressure is used providing 98% conversion at low maintenance costs.</p>
<p> ;</p>
<ol start="3">
<li><strong> Catalyst</strong></li>
</ol>
<p>&#8211; A catalyst neither takes part in a reaction nor increases the yield.</p>
<p>&#8211; It merely speeds up the reaction i.e. reduces the time taken to react at equilibrium of 450<sup>o</sup>C.</p>
<p>&#8211; Main catalyst is <strong>vanadium (V) oxide</strong> (V<sub>2</sub>O<sub>5</sub>).</p>
<p>&#8211; It is spread out (in trays) on silica gel to increase the surface area for combination of reactants.</p>
<p>&#8211; Dust settled in the catalyst may reduce its effective area.</p>
<p>&#8211; Dust may also react with the catalyst, Â<strong>poison</strong>Â it and further reduce its efficiency.</p>
<p>&#8211; This explains need to purify gases thoroughly.</p>
<p>&#8211; An effective catalyst is <strong>platinised asbestos</strong>.</p>
<p>&#8211; However, <strong>vanadium (V) oxide</strong> is preferred.</p>
<p> ;</p>
<h1>Reasons:</h1>
<p>&#8211; It is <strong>not easily poisoned </strong>by dust particles.</p>
<p>&#8211; It is cheaper and readily available.</p>
<p><strong><u> </u></strong></p>
<p><strong>Note</strong>:</p>
<p>&#8211; The highest yield of sulphur (VI) oxide is obtained at optimum conditions of 450<sup>0</sup>C and pressure 2-3 atmospheres in presence of vanadium (V) oxide or platinised asbestos.</p>
<p> ;</p>
<h2>Step 5: Heat exchanger reactions</h2>
<p>&#8211; Hot SO<sub>3 </sub>gas from catalytic chamber is again passed through heat exchanger for <strong>cooling </strong>after which the cooled gas is taken into an absorption chamber.</p>
<p> ;</p>
<h2>Step 6: Absorption chamber</h2>
<p>&#8211; The SO<sub>3</sub> is not dissolved (passed) into water directly.</p>
<p> ;</p>
<h2>Reason</h2>
<p>&#8211; It dissolves in water <strong>exothermically</strong> with a loud, hissing sound giving off corrosive vapour resulting into harmful sulphuric acid Âsprays or mist all around.</p>
<p> ;</p>
<p>&#8211; The SO<sub>3</sub> is dissolved in conc. H<sub>2</sub>SO<sub>4</sub> forming oleum (pyrosulphuric acid/ fuming sulphuric acid).</p>
<p> ;</p>
<h1>Equation:</h1>
<p> ;</p>
<p>SO<sub>3(g)</sub> + H<sub>2</sub>SO<sub>4(l)</sub> H<sub>2</sub>S<sub>2</sub>O<sub>7(l)</sub></p>
<p> ;</p>
<p>&#8211; Resultant Â<strong>Oleum</strong>Â is then channeled into a dilution chamber.</p>
<p> ;</p>
<p><strong>Step 7: Dilution chamber.</strong></p>
<p>&#8211; Oleum is diluted with correct amounts of water to form concentrated sulphuric acid.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p><strong> </strong></p>
<p>H<sub>2</sub>S<sub>2</sub>O<sub>7(l)</sub> + H<sub>2</sub>O<sub>(l) </sub> 2H<sub>2</sub>SO<sub>4(aq)</sub></p>
<p> ;</p>
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<p><strong>Summary: flow diagram for the contact process:</strong></p>
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<p><strong>Pollution control in contact process.</strong></p>
<p>&#8211; Main source of pollution is <strong>sulphur (IV) oxide</strong>.</p>
<p>&#8211; In catalyst chamber, SO<sub>2</sub> reacts with oxygen forming SO<sub>3</sub>.</p>
<h1></h1>
<h1>Equation: V<sub>2</sub>O<sub>5</sub></h1>
<p>2SO<sub>2(g)</sub> + O<sub>2(g)</sub> 2SO<sub>3(g)</sub> + Heat</p>
<p><strong>450<sup>o</sup>C</strong></p>
<p>&#8211; This is a reversible reaction and upto 98% conversion is possible and excess (unreacted) SO<sub>2</sub> warmed and released into atmosphere via long chimneys.</p>
<p>&#8211; However, SO<sub>2</sub> being a pollutant, little or none should be released into atmosphere.</p>
<p>&#8211; This is done by <strong>scrubbing the gas</strong>.</p>
<p>&#8211; This involves neutralizing the chimney gas by a solution of Calcium hydroxide forming a salt (calcium sulphite) and water.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Ca(OH)<sub>2(aq)</sub> + SO<sub>2(g) </sub> CaSO<sub>3(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; In certain cases, <strong>filters</strong> are also installed to remove any traces of acid spray or mist form the exhaust gases.</p>
<p>&#8211; The unreacted gases (SO<sub>2</sub> and SO<sub>3</sub>) may also be recycled within the process.</p>
<h1>Properties of concentrated sulphuric (VI) acid</h1>
<h1>Physical properties</h1>
<ol>
<li>&#8211; Colourless, odourless, oily liquid.</li>
<li>&#8211; Very dense; with density 1.84 gcm<sup>-3</sup>.</li>
<li>&#8211; Soluble in water and gives out considerable heat when a solution is formed.</li>
<li>&#8211; It is hygroscopic  absorbs atmospheric moisture to become wet.</li>
</ol>
<p> ;</p>
<p><strong>Experiment: To show hygroscopic nature of conc. H<sub>2</sub>SO<sub>4</sub>.</strong></p>
<p><strong>(i). Procedure</strong></p>
<p>&#8211; A small beaker half full of conc. H<sub>2</sub>SO<sub>4</sub> is weighed.</p>
<p>&#8211; Level of acid in beaker is marked to the outside using gummed paper.</p>
<p>&#8211; Acid is left exposed to air for a week or so then weighed again and level also noted.</p>
<p> ;</p>
<p><strong>(ii). Observations</strong></p>
<p>&#8211; There is an increase in weight of acid.</p>
<p>&#8211; Level of acid in beaker is now above the paper mark.</p>
<p> ;</p>
<p><strong>(iii). Explanations</strong></p>
<p>&#8211; The increase in weight and size is due to water absorbed form the air by the conc. sulphuric (VI) acid.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; This explains why sulphuric (VI) acid is used as a <strong>drying agent</strong>.</p>
<p> ;</p>
<h1>Chemical properties</h1>
<p> ;</p>
<ol start="5">
<li>&#8211; It is a <strong>dehydrating agent</strong>.</li>
</ol>
<p><strong>Examples:</strong></p>
<p><strong> </strong></p>
<p><strong>(a). Action on blue hydrated copper (II) sulphate (CuSO<sub>4</sub>.5H<sub>2</sub>O) crystals.</strong></p>
<p> ;</p>
<p><strong>(i). Procedure</strong></p>
<p>&#8211; A few crystals of hydrated CuSO<sub>4</sub>.5H<sub>2</sub>O were put in a test tube and enough concentrated sulphuric (VI) acid added, to cover them completely.</p>
<p> ;</p>
<p><strong>(ii). Observation:</strong></p>
<p>&#8211; Blue copper (II) sulphate pentahydrate crystals turn to white powder of anhydrous CuSO<sub>4</sub>.</p>
<p> ;</p>
<p><strong>Equation</strong></p>
<table>
<tbody>
<tr>
<td width="108"></td>
</tr>
<tr>
<td></td>
<td width="88">
<table width="100%">
<tbody>
<tr>
<td> Conc. H<sub>2</sub>SO<sub>4</sub></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p> ;</p>
<p>CuSO<sub>4</sub>.5H<sub>2</sub>O<sub>(s)</sub> CuSO<sub>4(s)</sub> + 5H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(Blue crystals) (White crystals)</em></strong></p>
<p> ;</p>
<p><strong>Explanations:</strong></p>
<p>&#8211; Conc.H<sub>2</sub>SO<sub>4</sub> has a very strong affinity for water and hence removes water of crystallization from crystals hence dehydrating them.</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>(b). Action on white sugar (C<sub>12</sub>H<sub>22</sub>O<sub>11</sub>)</strong></p>
<p><strong> </strong></p>
<p><strong>(i). Procedure: </strong></p>
<p>&#8211; A tablespoonful of sugar is put in an evaporating dish form a beaker and adequate volume of conc. H<sub>2</sub>SO<sub>4</sub> is added.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p>&#8211; Sugar turns form brown then <strong>yellow</strong> and finally to a <strong>charred black mass</strong> of <strong>carbon</strong>.</p>
<p>&#8211; A spongy black mass of charcoal (carbon) rises almost filling the dish.</p>
<p>&#8211; Steam is also give off and dish becomes very hot since reaction is exothermic.</p>
<p> ;</p>
<p><strong>Equation</strong></p>
<table>
<tbody>
<tr>
<td width="77"></td>
</tr>
<tr>
<td></td>
<td width="83">
<table width="100%">
<tbody>
<tr>
<td> Conc. H<sub>2</sub>SO<sub>4 </sub></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p> ;</p>
<p>C<sub>12</sub>H<sub>22</sub>O<sub>11(s)</sub> 12C<sub>(s)</sub> + 11H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(White crystals) (Black solid)</em></strong></p>
<p> ;</p>
<p><strong>Explanation</strong></p>
<p>&#8211; The acid removed from the sugar elements of water (hydrogen and oxygen, ratio 2:1) to form water, leaving behind a black charred mass of carbon.</p>
<p> ;</p>
<p><strong>(c). Action on oxalic acid (ethanedioic acid (H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>)</strong></p>
<p>&#8211; Conc. H<sub>2</sub>SO dehydrates oxalic acid on heating to a mixture of carbon (II) oxide and carbon (IV) oxide.</p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="88">
<table width="100%">
<tbody>
<tr>
<td> Conc. H<sub>2</sub>SO<sub>4</sub></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<h1>Equation</h1>
<p><strong> </strong></p>
<p>H<sub>2</sub>C<sub>2</sub>O<sub>4(s)</sub> CO<sub>(g)</sub> + CO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Note: </strong></p>
<p>&#8211; Conc. H<sub>2</sub>SO<sub>4</sub> acid gives severe skin burns because it removes water and elements of water from skin tissue.</p>
<p>&#8211; Should the acid spill on skin, it is washed immediately with plenty of <strong>water</strong> followed with a solution of <strong>sodium hydrogen carbonate</strong>.</p>
<p>&#8211; Holes appear where the acid spills on clothes for same reason.</p>
<p> ;</p>
<p><strong>(d). Action on alcohols (alkanols)</strong></p>
<p>&#8211; Conc. sulphuric (VI) acid dehydrates alcohols to corresponding alkenes.</p>
<p> ;</p>
<p><strong>Example: dehydration of ethanol to ethene</strong></p>
<p><strong>Equation:</strong></p>
<table>
<tbody>
<tr>
<td width="88">
<table width="100%">
<tbody>
<tr>
<td> Conc. H<sub>2</sub>SO<sub>4</sub></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p> ;</p>
<p>CH<sub>3</sub>CH<sub>2</sub>OH<sub>(s)</sub> C<sub>2</sub>H<sub>4(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(Ethanol) (Ethene)</em></strong></p>
<p> ;</p>
<p><strong>(e). Action on methanoic acid.</strong></p>
<p>&#8211; Conc. sulphuric (VI) acid dehydrates methanoic acid to form CO.</p>
<table>
<tbody>
<tr>
<td width="88">
<table width="100%">
<tbody>
<tr>
<td> Conc. H<sub>2</sub>SO<sub>4</sub></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p><strong>Equation:</strong></p>
<p><strong> </strong></p>
<p>HCOOH<sub>(s)</sub> CO<sub>(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong> </strong></p>
<ol start="6">
<li><strong> Further reactions of conc. H<sub>2</sub>SO<sub>4</sub> as an oxidizing agent.</strong></li>
</ol>
<p>&#8211; Hot concentrated Sulphuric acts as an oxidizing agent in which cases it is reduced to sulphur (IV) oxide and water.</p>
<p> ;</p>
<h2>Examples:</h2>
<p> ;</p>
<p><strong>(a). Reaction with metals.</strong></p>
<ul>
<li><strong>Copper</strong></li>
</ul>
<p>Cu<sub>(s)</sub> + 2H<sub>2</sub>SO<sub>4(l)</sub> CuSO<sub>4(aq)</sub> + SO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Note:</strong> the copper (II) sulphate formed is white since the conc. H<sub>2</sub>SO<sub>4</sub> further dehydrates the hydrated CuSO<sub>4</sub>.</p>
<p> ;</p>
<ul>
<li><strong>Zinc</strong></li>
</ul>
<p>Zn<sub>(s)</sub> + 2H<sub>2</sub>SO<sub>4(l)</sub> ZnSO<sub>4(aq)</sub> + SO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em> (Hot acid)</em></strong></p>
<p> ;</p>
<p>Zn<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(l)</sub> ZnSO<sub>4(aq)</sub> + H<sub>2(g)</sub></p>
<p><strong><em> (Cold acid)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>Lead</strong></li>
</ul>
<p>Pb<sub>(s)</sub> + 2H<sub>2</sub>SO<sub>4(l)</sub> PbSO<sub>4(aq)</sub> + SO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em> (Hot; conc.) (Insoluble)</em></strong></p>
<p> ;</p>
<p><strong>Note: </strong></p>
<p><strong>&#8211; Dilute</strong> sulphuric (VI) acid doesnÂt have any action on copper.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; Copper is below hydrogen in reactivity series hence cannot displace it from the acid.</p>
<p> ;</p>
<p>&#8211; This acid (H<sub>2</sub>SO<sub>4</sub>) has very little effects on lead, and usually the amount of SO<sub>2</sub> liberated is very little.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; Formation of an <strong>insoluble lead sulphate</strong> layer that forms a protective coating on the metal stopping further reaction.</p>
<p> ;</p>
<p><strong>(b). Reaction with non-metals.</strong></p>
<p>&#8211; Concentrated sulphuric acid <strong>oxidizes </strong>non-metals such as sulphur and carbon to their <strong>respective oxides</strong>.</p>
<p> ;</p>
<h2>Equations:</h2>
<h2>Ø With carbon</h2>
<p>C<sub>(s)</sub> + 2H<sub>2</sub>SO<sub>4(l)</sub> CO<sub>2(g)</sub> + 2SO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<h4>Ø With sulphur</h4>
<p>S<sub>(s)</sub> + 2H<sub>2</sub>SO<sub>4(l)</sub> 3SO<sub>2(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<ol start="8">
<li>It is a <strong>less volatile acid</strong>; and displaces more volatile acids (refer to lab preparation of HNO<sub>3</sub>)</li>
</ol>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Reactions of dilute sulphuric acid</strong></p>
<ol>
<li><strong> Reaction with metals</strong></li>
</ol>
<p>&#8211; It reacts with metals <strong>above hydrogen</strong> in the reactivity series to produce a <strong>salt</strong> and <strong>hydrogen</strong>.</p>
<p>&#8211; With potassium and sodium, reaction is <strong>violent</strong>.</p>
<p> ;</p>
<h1>Equations:</h1>
<ul>
<li><strong>With magnesium:</strong></li>
</ul>
<p>Mg<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> MgSO<sub>4(aq)</sub> + H<sub>2(g)</sub></p>
<p> ;</p>
<ul>
<li><strong>With zinc:</strong></li>
</ul>
<p>Zn<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> ZnSO<sub>4(aq)</sub> + H<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Copper is below hydrogen in reactivity series hence canÂt displace hydrogen form dilute sulphuric (VI) acid.</p>
<p> ;</p>
<ol start="2">
<li><strong> Reaction with carbonates and hydrogen carbonates</strong></li>
</ol>
<p>&#8211; Dilute H<sub>2</sub>SO<sub>4(aq)</sub> reacts with carbonates and hydrogen carbonates to produce a salt, carbon (IV) oxide and water.</p>
<p> ;</p>
<h1>Equations</h1>
<ul>
<li><strong>With sodium carbonate:</strong></li>
</ul>
<p>Na<sub>2</sub>CO<sub>3(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> Na<sub>2</sub>SO<sub>4(aq)</sub> + CO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<ul>
<li><strong>With calcium hydrogen carbonate:</strong></li>
</ul>
<p>CaHCO<sub>3(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> CaSO<sub>4(aq)</sub> + CO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Reaction with lead carbonate however stops soon after the reaction.</p>
<p> ;</p>
<h2>Reason:</h2>
<p>&#8211; Formation of an insoluble coating of the lead (II) sulphate on the lead (II) carbonate which prevents further contact between acid and carbonate.</p>
<p>&#8211; The same logic applies for calcium carbonate.</p>
<p><u> </u></p>
<ol start="3">
<li><strong> Reaction with oxides and hydroxides</strong></li>
</ol>
<p>&#8211; Reacts to form salt and water.</p>
<p>&#8211; However, those metal oxides whose sulphates are insoluble react only for a while.</p>
<p>&#8211; Thus reaction between dilute sulphuric (VI) acid and lead (II) oxide stops almost immediately.</p>
<p>&#8211; This is due to formation of an insoluble layer of lead (II) sulphate which effectively prevents further contact between acid and oxide.</p>
<p> ;</p>
<h1>Equations:</h1>
<ul>
<li><strong>With magnesium oxide:</strong></li>
</ul>
<p>MgO<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> MgSO<sub>4(aq)</sub> + H<sub>2</sub>O<sub>(g)</sub></p>
<p><strong><em>(White) (Colourless solution)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>With copper (II) oxide:</strong></li>
</ul>
<p>CuO<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> CuSO<sub>4(aq)</sub> + H<sub>2</sub>O<sub>(g)</sub></p>
<p><strong><em>(Black) (Blue solution)</em></strong></p>
<ul>
<li><strong>With sodium hydroxide:</strong></li>
</ul>
<p>NaOH<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> Na<sub>2</sub>SO<sub>4(aq)</sub> + 2H<sub>2</sub>O<sub>(g)</sub></p>
<p><strong><em>(White) (Colourless solution)</em></strong></p>
<p> ;</p>
<ul>
<li><strong>With lead (II) oxide:</strong></li>
</ul>
<p>PbO<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub> PbSO<sub>4(aq)</sub> + H<sub>2</sub>O<sub>(g)</sub></p>
<p><strong><em>(Red) (White ppt; reaction stops immediately)</em></strong></p>
<p> ;</p>
<h1>Uses of sulphuric (VI) acid</h1>
<ol>
<li>Manufacture of fertilizers.</li>
<li>Processing of metal ores.</li>
<li>Manufacture of detergents.</li>
<li>Manufacture of plastics.</li>
<li>Manufacture of dyes and paints.</li>
<li>Manufacture of lead and accumulators.</li>
<li>Manufacture of polymers.</li>
<li>Manufacture of petroleum (petroleum refinery).</li>
<li>Drying agent in industrial processes.</li>
</ol>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Hydrogen sulphide gas</strong></p>
<p>&#8211; It is a <strong>colourless gas</strong> with a characteristic Â<strong>rotten egg</strong>Â smell; and is usually given out by rotting cabbage and eggs.</p>
<p> ;</p>
<h2>Laboratory preparation</h2>
<p> ;</p>
<p><strong>(i). Apparatus:</strong></p>
<table>
<tbody>
<tr>
<td width="100">
<table width="100%">
<tbody>
<tr>
<td> Warm water</p>
<p> ;</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="64">
<table width="100%">
<tbody>
<tr>
<td>H<sub>2</sub>S<sub>(g)</sub></td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="100">
<table width="100%">
<tbody>
<tr>
<td>Iron (II) sulphide</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="76">
<table width="100%">
<tbody>
<tr>
<td> Dil. HCl</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="304">
<table width="100%">
<tbody>
<tr>
<td> Anhydrous Dry H<sub>2</sub>S gas</p>
<p>Calcium chloride</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="112">
<table width="100%">
<tbody>
<tr>
<td> Iron (II) sulphide</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="64">
<table width="100%">
<tbody>
<tr>
<td>Dil HCl</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<table>
<tbody>
<tr>
<td width="88">
<table width="100%">
<tbody>
<tr>
<td> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p>Or</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
<p><strong>(ii). Procedure: </strong></p>
<p>&#8211; Dilute hydrochloric acid is poured into Iron (II) sulphide in a round-bottomed flask.</p>
<p>&#8211; Resultant gas is passed through U-tube with anhydrous calcium chloride to dry the gas.</p>
<p>&#8211; This can also be done with <strong>phosphorous (V) oxide</strong>.</p>
<p> ;</p>
<h2>Equation:</h2>
<p>FeS<sub>(s)</sub> + 2HCl<sub>(aq)</sub> H<sub>2</sub>S<sub>(g)</sub> + FeCl<sub>2(aq)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>S<sup>2-</sup><sub>(aq)</sub> + H<sup>+</sup><sub>(aq) </sub> H<sub>2</sub>S<sub>(g)</sub></p>
<p> ;</p>
<p><strong>(iii). Collection of gas</strong></p>
<p>&#8211; When dry, the gas is collected by <strong>downward delivery</strong> because it is <strong>denser</strong> than air.</p>
<p>&#8211; When wet is collected over <strong>warm water</strong> because it is more soluble in cold water.</p>
<p> ;</p>
<ul>
<li><strong>Hydrogen sulphide test.</strong></li>
</ul>
<p>&#8211; When a strip of filter paper soaked in aqueous <strong>lead (II) ethanoate</strong> is put in hydrogen sulphide, the paper turns <strong>black or dark brown</strong>.</p>
<h2></h2>
<h2>Reason:</h2>
<p>&#8211; Due to the formation of lead (II) sulphide which is black.</p>
<p> ;</p>
<h2>Equation</h2>
<p>H<sub>2</sub>S<sub>(g)</sub> + (CH<sub>2</sub>COOH)<sub>2</sub>Pb<sub>(aq)</sub> PbS<sub>(s)</sub> + 2CH<sub>3</sub>COOH<sub>(aq)</sub></p>
<p> ;</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Properties of hydrogen sulphide gas</strong></p>
<p><strong>Physical properties</strong></p>
<ol>
<li>Colourless and very poisonous gas (similar to hydrogen cyanide)</li>
<li>Has a <strong>repulsive</strong> smell (similar to that of rotten eggs or decaying cabbages)</li>
<li><strong>Soluble</strong> in water giving a weak acid (only slightly ionized)</li>
</ol>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>H2<sub>S(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> H<sub>2</sub>S<sub>(aq)</sub></p>
<p> ;</p>
<h2>Then:</h2>
<p>H<sub>2</sub>S<sub>(aq)</sub> H<sup>+</sup><sub>(aq)</sub> + HS<sup>&#8211;</sup><sub>(aq)</sub> 2H<sup>+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; The acid is <strong>dibasic</strong> hence forms hydrogen sulphides.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2NaOH<sub>(aq)</sub> + H<sub>2</sub>S<sub>(g)</sub> NaHS<sub>(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong> </strong></p>
<p><strong>Note: </strong></p>
<p><strong>&#8211; </strong>Potassium hydroxide reacts similarly like sodium hydroxide.</p>
<p><strong> </strong></p>
<p><strong>Chemical properties </strong></p>
<ol start="4">
<li><strong> Combustion</strong></li>
</ol>
<p>&#8211; Burns in a <strong>blue flame</strong> in a limited supply of oxygen (air) forming a <strong>yellow deposit</strong> of sulphur and steam.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2H<sub>2</sub>S<sub>(g)</sub> + O<sub>2(g)</sub> 2SO<sub>2(s)</sub> + 2H<sub>2</sub>O<sub>(g)</sub></p>
<p> ;</p>
<p>&#8211; In plentiful supply (excess) of Oxygen (air) it burns with a blue flame forming SO<sub>2</sub> and steam.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2H<sub>2</sub>S<sub>(g)</sub> +3O<sub>2(g)</sub> 2S<sub>(s)</sub> + 2H<sub>2</sub>O<sub>(g)</sub></p>
<p> ;</p>
<ol start="5">
<li><strong> It is a reducing agent</strong></li>
</ol>
<p>&#8211; It supplies electrons which are accepted by the oxidizing agent and forms sulphur.</p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>H<sub>2</sub>S<sub>(aq)</sub> + 2H<sup>+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(aq)</sub></p>
<p> ;</p>
<h2>Then</h2>
<p>S<sup>2-</sup><sub>(aq)</sub> S<sub>(s)</sub> + 2e<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>H<sub>2</sub>S<sub>(aq)</sub> + [O] S<sub>(s)</sub> + H<sub>2</sub>O<sub>(l)</sub>; in terms of addition of oxygen.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<h1>Examples</h1>
<p>(i). With acidified K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> solution (potassium dichromate VI)</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p><strong><em>Reduction:</em></strong></p>
<table>
<tbody>
<tr>
<td width="23"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup><sub>(aq)</sub> + 3H<sub>2</sub>S<sub>(g)</sub> + 8H<sup>+</sup><sub>(aq)</sub> 2Cr<sup>3+</sup><sub>(aq)</sub> + 7H<sub>2</sub>O<sub>(l)</sub> + 3S<sub>(s)</sub></p>
<p><strong><em>(Orange) (Green)</em></strong></p>
<p> ;</p>
<p><strong><em> Oxidation</em></strong></p>
<p> ;</p>
<p><strong>Observation</strong>: The orange solution turns green and H<sub>2</sub>S oxidized to <strong>yellow sulphur.</strong></p>
<p> ;</p>
<p><strong>(ii). Potassium manganate (VII) (KMnO<sub>4</sub>)</strong></p>
<p><strong>Equation:</strong></p>
<p><strong><em>Reduction:</em></strong></p>
<table>
<tbody>
<tr>
<td width="23"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>2MnO<sub>4</sub><sup>&#8211;</sup><sub>(aq)</sub> + 5H<sub>2</sub>S<sub>(g)</sub> + 6H<sup>+</sup><sub>(aq)</sub> 2Mn<sup>2+</sup><sub>(aq)</sub> + 8H<sub>2</sub>O<sub>(l)</sub> + 5S<sub>(s)</sub></p>
<p><strong><em>(Purple) (Colourless)</em></strong></p>
<p> ;</p>
<p><strong><em> Oxidation</em></strong></p>
<p><strong>Observation</strong>:</p>
<p>&#8211; The Purple solution turns colourless</p>
<p>&#8211; Manganate (VII) ions are reduced to manganate (II) ions; H<sub>2</sub>S oxidized to <strong>yellow sulphur.</strong></p>
<p> ;</p>
<p><strong>(iii). Action on Iron (III) chloride ions</strong></p>
<p><strong>Equation:</strong></p>
<p>FeCl<sub>3(aq)</sub> + H<sub>2</sub>S<sub>(g) </sub> 2FeCl<sub>2(aq)</sub> + 2HCl<sub>(aq)</sub> + S<sub>(s)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p><strong><em>Reduction:</em></strong></p>
<table>
<tbody>
<tr>
<td width="23"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Fe<sup>3+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(g)</sub> Fe<sup>2+</sup><sub>(aq)</sub> + 3S<sub>(s)</sub></p>
<p><strong><em>(Brown) (Pale green)</em></strong></p>
<p> ;</p>
<p><strong><em> Oxidation</em></strong></p>
<p> ;</p>
<p><strong>Observation</strong>:</p>
<p>&#8211; The brown solution turns pale green;</p>
<p>&#8211; The Fe<sup>3+</sup><sub>(aq)</sub> are reduced to Fe<sup>2+</sup><sub>(aq)</sub>; while the S<sup>2-</sup><sub>(aq)</sub> are oxidized to yellow sulphur.</p>
<p> ;</p>
<p><strong>(iv). Action with Conc. HNO<sub>3</sub></strong></p>
<p><strong>Equation:</strong></p>
<p>2HNO<sub>3(aq)</sub> + H<sub>2</sub>S<sub>(g) </sub> 2H<sub>2</sub>O<sub>(aq)</sub> + 2NO<sub>2(aq)</sub> + S<sub>(s) </sub>+ Heat</p>
<p><strong> </strong></p>
<p><strong>Ionically:</strong></p>
<p><strong><em>Reduction:</em></strong></p>
<table>
<tbody>
<tr>
<td width="0"></td>
<td width="2"></td>
<td width="58"></td>
<td width="295"></td>
</tr>
<tr>
<td></td>
<td colspan="2"></td>
<td rowspan="3"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
<tr>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>2H<sup>+</sup><sub>(aq)</sub> + 2NO<sub>3</sub><sup>&#8211;</sup><sub>(aq)</sub> + H<sup>+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(aq)</sub> 2H<sub>2</sub>O<sub>(l)</sub> + 2NO<sub>2(g)</sub> + S<sub>(s) </sub>+ Heat</p>
<p><strong><em>(Colourless solution) (Brown) (Yellow)</em></strong></p>
<p> ;</p>
<p><strong><em> Oxidation</em></strong></p>
<p><strong>Observation</strong>:</p>
<p>&#8211; Evolution of brown fumes; and deposits of a yellow solid;</p>
<p>&#8211; HNO<sub>3(aq)</sub> is reduced to <strong>brown NO<sub>2(g)</sub></strong>; while S<sup>2-</sup><sub>(aq)</sub> are oxidized to <strong>yellow sulphur</strong>;</p>
<p><strong>Note: </strong>The solution also contains H<sub>2</sub>SO<sub>4</sub> produced by the reaction:</p>
<p><strong><em>Reduction</em></strong></p>
<p> ;</p>
<p> ;</p>
<p>2HNO<sub>3(aq)</sub> + H<sub>2</sub>S<sub>(g) </sub> H<sub>2</sub>SO<sub>4(aq)</sub> + 8NO<sub>2(aq)</sub> + 4H<sub>2</sub>O<sub>(l) </sub>;</p>
<table>
<tbody>
<tr>
<td width="95"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong><em>Oxidation</em></strong></p>
<p> ;</p>
<p><strong>(v). Action of air on H<sub>2</sub>S</strong></p>
<p>&#8211; The gas is dissolved in distilled water in a beaker and exposed to air; after a few days, <strong>a</strong> <strong>white disposal</strong> is formed.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>H<sub>2</sub>S<sub>(g)</sub> + O<sub>2(g)</sub> 2H<sub>2</sub>O<sub>(l)</sub> + 2S<sub>(s)</sub></p>
<p> ;</p>
<p><strong>(vi). Action with concentrated sulphuric (VI) acid.</strong></p>
<p> ;</p>
<p><strong>Equation</strong></p>
<p><strong><em>Reduction</em></strong></p>
<p> ;</p>
<p> ;</p>
<p>H<sub>2</sub>SO<sub>4(aq)</sub> + 3H<sub>2</sub>S<sub>(g) </sub> 4S<sub>(s)</sub> + 4H<sub>2</sub>O<sub>(l)</sub></p>
<table>
<tbody>
<tr>
<td width="95"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong><em>Oxidation</em></strong></p>
<p> ;</p>
<p><strong>(vii). Action with halogen elements</strong></p>
<ul>
<li><strong>Red-brown bromine water</strong></li>
</ul>
<p>&#8211; Red-brown bromine water is <strong>reduced</strong> forming colourless hydrogen bromide (Hydrobromic acid) and <strong>yellow </strong>deposits (suspension) of sulphur.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p><strong><em>Reduction</em></strong></p>
<table>
<tbody>
<tr>
<td width="11"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Br<sub>2(aq)</sub> + H<sub>2</sub>S<sub>(g) </sub> 2HBr<sub>(aq)</sub> + S<sub>(s)</sub></p>
<p><strong><em>(Red-brown) (Colourless) (Yellow suspension)</em></strong></p>
<p> ;</p>
<p><strong><em>Oxidation</em></strong></p>
<p> ;</p>
<p><strong>(viii). Action with hydrogen peroxide.</strong></p>
<p><strong>Equation:</strong></p>
<p><strong><em>Reduction</em></strong></p>
<table>
<tbody>
<tr>
<td width="11"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>H<sub>2</sub>O<sub>2(aq)</sub> + H<sub>2</sub>S<sub>(g) </sub> 2H<sub>2</sub>O<sub>(l)</sub> + S<sub>(s)</sub></p>
<p><strong><em>(Red-brown) (Colourless) (Yellow suspension)</em></strong></p>
<p> ;</p>
<p><strong><em>Oxidation</em></strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong> </strong></p>
<h1>Preparation of metallic sulphides</h1>
<p>&#8211; Hydrogen sulphide reacts with metal ions in solution to form precipitates of metal sulphides; majority of which are black in colour.</p>
<p> ;</p>
<p><strong>(i). Procedure</strong></p>
<p>&#8211; The gas is bubbled through solutions of the following salts: Pb (NO<sub>3</sub>)<sub>2</sub>, CuSO<sub>4</sub>, FeSO<sub>4</sub> etc.</p>
<p><strong> </strong></p>
<p><strong>(ii). Observations and equations</strong></p>
<ul>
<li><strong>Lead ions:</strong></li>
</ul>
<p>Pb(NO<sub>3</sub>)<sub>2(aq)</sub> + H<sub>2</sub>S<sub>(aq) </sub> PbS<sub>(s)</sub> + 2HNO<sub>3(aq)</sub></p>
<p><strong><em>(Colourless) (Black)</em></strong></p>
<p><strong> </strong></p>
<p><strong>Ionically:</strong></p>
<p>Pb<sup>2+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(aq)</sub> PbS<sub>(s)</sub></p>
<p> ;</p>
<ul>
<li><strong>Copper (II) ions:</strong></li>
</ul>
<p>CuSO<sub>4(aq)</sub> + H<sub>2</sub>S<sub>(aq) </sub> CuS<sub>(s)</sub> + H<sub>2</sub>SO<sub>4(aq)</sub></p>
<p><strong><em>(Blue) (Black)</em></strong></p>
<p><strong> </strong></p>
<p><strong>Ionically:</strong></p>
<p>Cu<sup>2+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(aq)</sub> CuS<sub>(s)</sub></p>
<p> ;</p>
<ul>
<li><strong>Iron (II) ions:</strong></li>
</ul>
<p>FeSO<sub>4(aq)</sub> + H<sub>2</sub>S<sub>(aq) </sub> FeS<sub>(s)</sub> + H2SO<sub>4(aq)</sub></p>
<p><strong><em>(Pal green) (Black)</em></strong></p>
<p><strong> </strong></p>
<p><strong>Ionically:</strong></p>
<p>Fe<sup>2+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(aq)</sub> FeS<sub>(s)</sub></p>
<p><strong> </strong></p>
<ul>
<li><strong>Zinc ions:</strong></li>
</ul>
<p>Zn(NO<sub>3</sub>)<sub>2(aq)</sub> + H<sub>2</sub>S<sub>(aq) </sub> ZnS<sub>(s)</sub> + 2HNO<sub>3(aq)</sub></p>
<p><strong><em>(Colourless) (Black)</em></strong></p>
<p><strong> </strong></p>
<p><strong>Ionically:</strong></p>
<p>Zn<sup>2+</sup><sub>(aq)</sub> + S<sup>2-</sup><sub>(aq)</sub> ZnS<sub>(s)</sub></p>
<p><strong> </strong></p>
<p><strong>Note:</strong></p>
<p>&#8211; Most metal sulphides are <strong>insoluble</strong> in water except those of sodium, potassium and ammonium.</p>
<p> ;</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong>Sulphites</strong></p>
<p>&#8211; Are compounds of the sulphite radical (SO<sub>3</sub><sup>2-</sup>) and a metallic or ammonium cation</p>
<p><strong> </strong></p>
<p><strong>Effects of heat</strong></p>
<p>&#8211; They decompose on heating, forming SO<sub>2</sub>;</p>
<p> ;</p>
<p><strong>Example:</strong></p>
<p>CuSO<sub>3(s)</sub> <sup>Heat</sup> CuO<sub>(s)</sub> + SO<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Test for sulphites</strong></p>
<p> ;</p>
<h1>(i). Procedure</h1>
<p>&#8211; To 2cm<sup>3</sup> of the test solution, ad 2 cm<sup>3</sup> of BaCl<sub>2</sub> or Ba (NO<sub>3</sub>)<sub>2</sub>; i.e. addition of barium ions.</p>
<p>&#8211; To the mixture add 2 cm<sup>3</sup> of dilute HCl or HNO<sub>3</sub>.</p>
<p> ;</p>
<h2>(ii). Observation</h2>
<p>&#8211; A <strong>white precipitate</strong> (BaSO<sub>3</sub>) is formed which <strong>dissolves on addition of acid</strong>.</p>
<p>&#8211; Production of a colourless gas that turns filter paper soaked in acidified <strong>orange</strong> potassium dichromate (VI) to <strong>green.</strong></p>
<p> ;</p>
<h1>(iii). Explanations</h1>
<p>&#8211; Only BaSO<sub>3</sub>; BaCO<sub>3</sub> and BaSO<sub>4</sub> form white precipitates;</p>
<p>&#8211; The precipitates of BaSO<sub>3</sub> and BaCO<sub>3</sub> dissolve on addition of dilute acids; unlike BaSO<sub>4</sub>;</p>
<p>&#8211; BaSO<sub>3</sub> produces SO<sub>2(g)</sub> as it dissolves on addition of a dilute acid; SO<sub>2</sub> turns orange acidified potassium dichromate (VI) to green;</p>
<p>&#8211; BaCO<sub>3</sub> of the other hand dissolves in dilute acids producing CO<sub>2</sub>; which has no effect on K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>; but forms a white precipitate in lime water;</p>
<p> ;</p>
<h1>Equations:</h1>
<ul>
<li><strong>On addition of Ba<sup>2+</sup>:</strong></li>
</ul>
<p>Ba<sup>2+</sup><sub>(aq)</sub> + SO<sub>3</sub><sup>2-</sup><sub>(aq) </sub> BaSO<sub>3(s)</sub></p>
<p><strong><em>(White precipitate)</em></strong></p>
<p><strong> </strong></p>
<ul>
<li><strong>On addition of dilute HCl(aq):</strong></li>
</ul>
<p>BaSO<sub>3(s)</sub> + 2HCl<sub>(aq)</sub> BaCl<sub>2(aq)</sub> + SO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong><em>(White precipitate) (Colourless)</em></strong></p>
<p><strong> </strong></p>
<p><strong>Ionically:</strong></p>
<p>BaSO<sub>3(s)</sub> + 2H<sup>+</sup><sub>(aq)</sub> Ba<sup>2+</sup><sub>(aq)</sub> + SO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong> </strong></p>
<h1>Sulphates</h1>
<p>&#8211; Are compounds of the sulphate radical (SO<sub>4</sub><sup>2-</sup>) and a metallic or ammonium cation.</p>
<p><strong><u> </u></strong></p>
<p><strong>Effects of heat.</strong></p>
<p>&#8211; Decompose on heating and liberate SO<sub>2</sub> and SO<sub>3 </sub>or SO<sub>3 </sub>alone;</p>
<p>&#8211; However quite a number of sulphates do not decompose on heating; and thus require <strong>very strong heating</strong> in order to decompose.</p>
<p> ;</p>
<p><strong>Examples:</strong></p>
<p>2FeSO<sub>4(s)</sub> <sup>Heat</sup> Fe<sub>2</sub>O<sub>3(s)</sub> + SO<sub>2(g)</sub> + SO<sub>3(g)</sub></p>
<p><strong><em>(Pale green) (Brown) (Colourless gases)</em></strong></p>
<p> ;</p>
<p>CuSO<sub>4(s)</sub> <sup>Heat</sup> CuO<sub>(s)</sub> + SO<sub>3(g)</sub></p>
<p><strong><em>(Blue) (Black) (Colourless)</em></strong></p>
<h1>Action of acids</h1>
<h1>Test for sulphates</h1>
<p>&#8211; To about 2 cm<sup>3</sup> of the test solution, 2 cm<sup>3</sup> of BaCl<sub>2</sub> or Ba (NO<sub>3</sub>)<sub>2</sub> solution is added.</p>
<p>&#8211; To the mixture, 2 cm<sub>3</sub> of dilute HCl or HNO<sub>3</sub> is added.</p>
<p> ;</p>
<h1>Observation</h1>
<p>&#8211; A white precipitate is formed when Ba (NO<sub>3</sub>)<sub>2</sub> is added; which is insoluble in excess acid.</p>
<p> ;</p>
<p><strong>Explanations.</strong></p>
<p>&#8211; Only BaSO<sub>3</sub>; BaCO<sub>3</sub> and BaSO<sub>4</sub> form white precipitates;</p>
<p>&#8211; The precipitates of BaSO<sub>3</sub> and BaCO<sub>3</sub> dissolve on addition of dilute acids; unlike BaSO<sub>4</sub>;</p>
<p>&#8211; Thus the white precipitate insoluble in dilute HCl or HNO<sub>3</sub> could only be a <strong>sulphate</strong>; in this case barium sulphate.</p>
<p> ;</p>
<h1>Equations:</h1>
<ul>
<li><strong>On addition of Ba<sup>2+</sup>:</strong></li>
</ul>
<p> ;</p>
<p>Ba<sup>2+</sup><sub>(aq)</sub> + SO<sub>4</sub><sup>2-</sup><sub>(aq) </sub> BaSO<sub>4(s)</sub></p>
<p><strong><em> (white precipitate)</em></strong></p>
<p><strong> </strong></p>
<ul>
<li><strong>On addition of dilute acid:</strong></li>
</ul>
<p>BaSO<sub>4(s)</sub> + 2HCl<sub>(aq)</sub> BaSO<sub>4(s)</sub> + 2HCl<sub>(aq)</sub>; i.e. no effect;</p>
<p><strong><em>(White precipitate) (White precipitate)</em></strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Pollution by sulphur compounds.</strong></p>
<p>&#8211; Main pollutants are <strong>sulphur (IV) Oxide</strong> and <strong>hydrogen sulphide.</strong></p>
<p> ;</p>
<p><strong>(a). Sulphur (IV) oxide.</strong></p>
<p>&#8211; SO<sub>2</sub> is emitted when sulphur-containing fuels are burnt; during extraction of metals like copper and in manufacture of sulphuric (VI) acid.</p>
<p>&#8211; SO<sub>2</sub> is oxidized to SO<sub>3</sub>;</p>
<p>&#8211; SO<sub>3</sub> reacts with water in atmosphere to form sulphuric (VI) acid which comes down as acid rain or acid fog.</p>
<p>Acid rain (fog) has environmental effects:</p>
<ul>
<li>Leaching of minerals in soil;</li>
<li>Erosion of stone work on buildings;</li>
<li>Corrosion of metallic structures;</li>
<li>Irritation of respiratory systems thus worsening respiratory illnesses;</li>
<li>Death of plants as a result of defoliation (falling of leaves);</li>
<li>Destruction of aquatic life in acidified lakes;</li>
<li>Stunted plant growth due to chlorosis;</li>
</ul>
<p> ;</p>
<p>(b). H<sub>2</sub>S is very poisonous.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>UNIT 5: CHLORINE AND ITS COMPOUNDS.</strong></p>
<p><strong><em>Unit Checklist:</em></strong></p>
<ol>
<li>About chlorine.</li>
<li>Preparation of chlorine.</li>
<li>Properties of chlorine.</li>
</ol>
<ul>
<li>Colour and smell</li>
<li>Solubility in water</li>
<li>Action on litmus paper</li>
<li>Bleaching action</li>
<li>Action on hot metals</li>
<li>Reaction with non-metals</li>
<li>Oxidation reactions</li>
<li>Reaction with alkalis</li>
<li>Effect of sunlight on chlorine water.</li>
</ul>
<ol start="4">
<li>Industrial manufacture of chlorine (The mercury cathode cell)</li>
<li>Uses of chlorine and its compounds</li>
<li>Hydrogen chloride gas</li>
</ol>
<ul>
<li>Preparation</li>
<li>Properties</li>
</ul>
<ol start="7">
<li>Test for chlorides.</li>
<li>Hydrochloric acid</li>
</ol>
<ul>
<li>Large scale manufacture</li>
<li>Uses of hydrochloric acid</li>
</ul>
<ol start="9">
<li>Environmental pollution of chlorine and its compounds</li>
</ol>
<p> ;</p>
<p><strong>Introduction:</strong></p>
<p>&#8211; Chlorine is a molecular non-metallic element made up of diatomic molecules.</p>
<p>&#8211; Its electron arrangement is 2.8.7 and it belongs to the halogen family.</p>
<p> ;</p>
<p><strong>Preparation of chlorine.</strong></p>
<p><strong>Note:</strong> It is usually prepared by oxidation of concentrated hydrochloric acid by removal of hydrogen.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>2HCl<sub>(aq)</sub> + [O] Cl<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub></p>
<p>&#8211; The [O] is from a substance containing oxygen.</p>
<p> ;</p>
<p><strong>(a). Preparation of chlorine from MnO<sub>2</sub> and HCl.</strong></p>
<p><strong>(i). Apparatus:</strong></p>
<p><strong> </strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Conditions:</strong></p>
<p>&#8211; Heating;</p>
<p>&#8211; Presence of an oxidizing agent; in this case it is manganese (IV) oxide.</p>
<p> ;</p>
<p><strong>(iii). Procedure:</strong></p>
<p>&#8211; Hydrochloric acid is reacted with manganese (IV) oxide (dropwise);</p>
<p><strong>Equation:</strong></p>
<p>MnO<sub>2(s)</sub> + 4HCl<sub>(aq)</sub> <sup>Heat</sup> MnCl<sub>2(aq)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + Cl<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>(iv). Explanation:</strong></p>
<p>&#8211; Manganese (IV) oxide oxidizes hydrochloric acid by removing hydrogen resulting into chlorine.</p>
<p>&#8211; The manganese (IV) oxide is reduced to water and manganese chloride.</p>
<p>&#8211; The resultant chlorine gas is passed through a bottle containing water.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; To remove hydrogen chloride fumes (gas) which is very soluble in water.</p>
<p>&#8211; Next it is passed through concentrated sulphuric acid or anhydrous calcium chloride; to dry the gas.</p>
<p> ;</p>
<p><strong>(v). Collection:</strong></p>
<p>(a). Wet chlorine is collected over brine (saturated sodium chloride solution) or hot water.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; It does not dissolve in brine and is less soluble in water</p>
<p> ;</p>
<p>(b). Dry chlorine is collected by downward delivery (upward displacement of air)</p>
<p><strong>Reason:</strong></p>
<p>&#8211; It is denser than air (2.5 times).</p>
<p><strong>Note:</strong></p>
<p>&#8211; Chlorine may also be dried by adding calcium chloride to the jar of chlorine.</p>
<p> ;</p>
<p>(c). The first bottle must contain water and the second concentrated sulphuric acid.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; If the gas is first passed through concentrated sulphuric acid in the first bottle then to the water; it will be made wet again.</p>
<p> ;</p>
<p><strong>Properties of chlorine gas.</strong></p>
<ol>
<li><strong> Colour and smell.</strong></li>
</ol>
<p><strong>Caution:</strong> Chlorine is <strong>very poisonous</strong>.</p>
<p>&#8211; It is a green-yellow gas with an irritating pungent smell that attacks the nose and the lungs.</p>
<p>&#8211; It is 2.5 times denser than air, hence can be collected by downward delivery.</p>
<p> ;</p>
<ol start="2">
<li><strong> Solubility in water.</strong></li>
</ol>
<p>&#8211; It is fairly soluble in water forming green-yellow chlorine water.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Cl<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> HCl<sub>(aq)</sub> + HOCl<sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; Chlorine water is composed of two acids; chloric (I) acid (hypochlorous acid) and hydrochloric acid.</p>
<p> ;</p>
<ol start="3">
<li><strong> Action on litmus paper.</strong></li>
</ol>
<p>&#8211; Moist chlorine turns litmus paper red then bleaches it.</p>
<p>&#8211; Dry chlorine turns damp blue litmus paper red then bleaches it.</p>
<p>&#8211; Moist chlorine bleaches red litmus paper; dry chlorine bleaches damp red litmus paper.</p>
<p>&#8211; Dry chlorine has no effect on dry litmus paper.</p>
<p><strong>Reasons:</strong></p>
<p>(i). In presence of moisture chlorine forms chlorine water which is acidic and hence turns blue litmus paper red.</p>
<p>(ii). Hypochlorous acid in the chlorine water is an oxidizing agent; thus adds oxygen (oxidizes) to the colour of most dyes; hence bleaching it.</p>
<p><strong> </strong></p>
<p><strong>Equations:</strong></p>
<p>Cl<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> HCl<sub>(aq)</sub> + HOCl<sub>(aq)</sub></p>
<table>
<tbody>
<tr>
<td width="191"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Acidic solution</p>
<p>Then:</p>
<p>Dye + HOCl<sub>(aq)</sub> HCl<sub>(aq)</sub> + {Dye + [O]}</p>
<p>Coloured Colourless</p>
<p><strong> </strong></p>
<ol start="4">
<li><strong> Bleaching action.</strong></li>
</ol>
<p>&#8211; Moist chlorine bleaches dyes but not printers ink which is made of <strong>carbon</strong>.</p>
<p>&#8211; The colour change is due to oxidation by hypochlorous acid.</p>
<p><strong> </strong></p>
<p><strong>Equations:</strong></p>
<p>Cl<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> HCl<sub>(aq)</sub> + HOCl<sub>(aq)</sub></p>
<p> ;</p>
<p> ;</p>
<p>Acidic solution</p>
<p>Then:</p>
<p>Dye + HOCl<sub>(aq)</sub> HCl<sub>(aq)</sub> + {Dye + [O]}</p>
<p>Coloured Colourless</p>
<ol start="5">
<li><strong> Action on a burning splint.</strong></li>
</ol>
<p>&#8211; The gas <strong>put out</strong> a glowing splint. It does not burn.</p>
<p> ;</p>
<ol start="6">
<li><strong> Action on hot metals.</strong></li>
</ol>
<p><strong>(a). Preparation of iron (III) chloride.</strong></p>
<p><strong>(i). Apparatus.</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Precaution. </strong></p>
<p>&#8211; Experiment should be done in a fume cupboard or in the open.</p>
<p>Reason:</p>
<p>&#8211; Chlorine gas is poisonous and will thus be harmful to the human body.</p>
<p> ;</p>
<p><strong>(iii). Procedure:</strong></p>
<p>&#8211; Dry chlorine gas is passed over iron wool as per the diagram.</p>
<p> ;</p>
<p><strong>(iv). Conditions.</strong></p>
<ul>
<li>Chlorine gas has to be dry (done by the anhydrous calcium chloride in the U-tube)</li>
</ul>
<p><strong>Reason:</strong></p>
<p>To prevent <strong>hydration</strong> hence <strong>oxidation</strong> of iron (which will then form Fe<sub>2</sub>O<sub>3</sub>.5H<sub>2</sub>O) hence preventing reaction between iron and chlorine.</p>
<p> ;</p>
<ul>
<li>Iron metal must be <strong>hot</strong>; and this is done by heating.</li>
</ul>
<p><strong>Reason: </strong></p>
<p>To provide <strong>activation energy</strong> i.e. the minimum kinetic energy which the reactants must have to form products.</p>
<p> ;</p>
<ul>
<li>Anhydrous calcium chloride.</li>
</ul>
<p>&#8211; In the U-tube; to <strong>dry</strong> the chlorine gas.</p>
<p>&#8211; In the thistle funnel; to prevent <strong>atmospheric water vapour</strong> (moisture) from getting into the apparatus and hence reacting with iron (III) chloride.</p>
<p> ;</p>
<p><strong>(v). Observations:</strong></p>
<p>&#8211; Iron metal glows red-hot.</p>
<p>&#8211; Red brown fumes (FeCl<sub>3(g)</sub>) are formed in the combustion tube.</p>
<p>&#8211; A black solid (FeCl<sub>3(s)</sub>) is collected in the flask.</p>
<p><strong>Note:</strong></p>
<p>&#8211; Iron (III) chloride cannot be easily collected in the combustion tube.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; It sublimes when heated and hence the hotter combustion tube causes it to sublime and its vapour is collected on the cooler parts of the flask.</p>
<p> ;</p>
<p><strong>(vi). Reaction equation.</strong></p>
<p>2Fe<sub>(s)</sub> + 3Cl<sub>2(g)</sub> 2FeCl<sub>3(g)</sub></p>
<p> ;</p>
<p><strong>(vii). Conclusion.</strong></p>
<p>&#8211; Iron (III) chloride sublimes on heating; the black solid changes to red-brown fumes on heating.</p>
<p><strong>Equation:</strong></p>
<p>FeCl<sub>3(s)</sub> FeCl<sub>3(g)</sub></p>
<p>(black) (Red-brown)</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong>(b). Aluminium chloride.</strong></p>
<p>2Al<sub>(s)</sub> + 3Cl<sub>2(g)</sub> 2FeCl<sub>2(s)</sub></p>
<p>2Al<sub>(s)</sub> + 3Cl<sub>2(g)</sub> Al<sub>2</sub>Cl<sub>6(s)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Aluminium chloride also <strong>sublimes</strong> on heating.</p>
<p><strong>Equation:</strong></p>
<p>AlCl<sub>3(s)</sub> AlCl<sub>3(g)</sub></p>
<p>(White) (White)</p>
<p> ;</p>
<p><strong>(c). Reaction with burning magnesium.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; Burning magnesium is lowered into a gar jar of chlorine gas.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p>&#8211; The magnesium continues to <strong>burn</strong> with a <strong>bright blinding flame</strong>;</p>
<p>&#8211; Formation of <strong>white fumes</strong> (MgCl<sub>2</sub>); which cools into a white powder.</p>
<p> ;</p>
<p><strong>(iii). Equation:</strong></p>
<p>Mg<sub>(s)</sub> + Cl<sub>2(g) </sub> MgCl<sub>2(s)</sub></p>
<p> ;</p>
<p>&#8211; Generally chlorine reacts with most metals when hot top form corresponding chlorides.</p>
<p><strong>Note:</strong></p>
<p>Where a metal forms two chlorides when it reacts with chlorine, the higher chloride is usually formed.</p>
<p><strong>Reason:</strong></p>
<p>The higher chloride is <strong>stable.</strong> This explains why reactions of chlorine with iron results into iron (III) chloride and not iron (II) chloride.</p>
<p> ;</p>
<p> ;</p>
<ol start="7">
<li><strong> Reaction with non-metals.</strong></li>
</ol>
<p>&#8211; It reacts with hot metals; forming covalent molecular compounds.</p>
<p> ;</p>
<p><strong>(a). Reaction with phosphorus.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; A piece of warm phosphorus is lowered into a gas jar of chlorine.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p>&#8211; Phosphorus begins to <strong>smoulder</strong> and then ignites spontaneously.</p>
<p>&#8211; Evolution of <strong>white fumes</strong> (PbCl<sub>3</sub> and PCl<sub>5</sub>)</p>
<p> ;</p>
<p><strong>(iv). Explanation.</strong></p>
<p>&#8211; Chlorine reacts with warm dry phosphorus to form white fumes of phosphorus (III) and (V) chlorides.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>P<sub>4(s)</sub> + 6Cl<sub>2(g) </sub> 4PCl<sub>3(s)</sub></p>
<p>(With limited chlorine)</p>
<p>P<sub>4(s)</sub> + 10Cl<sub>2(g)</sub> 4PCl<sub>5(s)</sub></p>
<p>(With excess chlorine)</p>
<p> ;</p>
<p><strong>(b). Reaction with hydrogen.</strong></p>
<p><strong>(i). Conditions:</strong></p>
<p>&#8211; Heating or <strong>presence of light</strong>; since chlorine and hydrogen do not react with each other at room temperature.</p>
<p> ;</p>
<p><strong>(ii). Precaution:</strong></p>
<p>&#8211; The experiment is performed in a <strong>fume chamber</strong> (cupboard); since the reaction is <strong>explosive</strong>;</p>
<p> ;</p>
<p><strong>(iii). Procedure:</strong></p>
<p>&#8211; Chlorine gas is mixed with hydrogen gas and the mixture heated or exposed to direct light; then aqueous ammonia brought near the mouth of the jar.</p>
<p> ;</p>
<p><strong>(iv). Observations:</strong></p>
<p>&#8211; <strong>White fumes</strong> at the mouth of the jar.</p>
<p> ;</p>
<p><strong>(v). Explanations:</strong></p>
<p>&#8211; Chlorine reacts explosively with hydrogen to form hydrogen chloride gas.</p>
<p><strong>Equation:</strong></p>
<p>Cl<sub>2(g)</sub> + H<sub>2(g) </sub><sup>Heat/ Light</sup> 2HCl<sub>(g).</sub></p>
<p> ;</p>
<p>&#8211; The hydrogen chloride gas diffuses upwards and reacts with ammonia at the mouth of the test tube to form white fumes of ammonium chloride; NH<sub>4</sub>Cl.</p>
<p>Equation:</p>
<p>HCl<sub>(g)</sub> + NH<sub>3(g)</sub> NH<sub>4</sub>Cl<sub>(g)</sub></p>
<p>White fumes.</p>
<p> ;</p>
<ol start="8">
<li><strong> Chlorine as an oxidizing agent.</strong></li>
</ol>
<p>&#8211; Chlorine is a strong <strong>oxidizing agent</strong> and oxidizes many ions, by readily accepting electrons.</p>
<p>&#8211; During the process, chlorine itself undergoes reduction.</p>
<p> ;</p>
<p><strong>(a). Reaction with hydrogen sulphide gas.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; A gas jar full of chlorine gas is inverted into another containing hydrogen sulphide gas.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Apparatus:</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; <strong>Yellow</strong> deposits (of sulphur)</p>
<p>&#8211; <strong>Misty</strong> fumes (hydrogen chloride gas)</p>
<p> ;</p>
<p><strong>(iv). Explanations:</strong></p>
<p>&#8211; Chlorine oxidizes hydrogen sulphide gas to sulphur solid, while itself is reduced to hydrogen chloride gas.</p>
<p><strong>Equation: </strong> <strong><sub>Oxidation</sub></strong></p>
<table>
<tbody>
<tr>
<td width="59"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Cl<sub>2(g)</sub> + H<sub>2</sub>S<sub>(g)</sub> 2HCl<sub>(g) </sub>+ S<sub>(s)</sub></p>
<table>
<tbody>
<tr>
<td width="11"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong><sup>Reduction</sup></strong></p>
<p><strong>(v). Conditions:</strong></p>
<p>&#8211; At least one of the gases must be <strong>moist</strong>; they do not react with each other in absence of moisture.</p>
<p><strong>Note:</strong></p>
<p>&#8211; In absence of moisture both gases are still in molecular form and hence cannot react; water facilitates their ionization hence ability to react.</p>
<p> ;</p>
<p>&#8211; If aqueous hydrogen sulphide is used, then sulphur forms as a <strong>yellow suspension</strong> on the acidic solution.</p>
<p><strong>Equations:</strong></p>
<p><strong><em>Stoichiometric:</em></strong></p>
<p>Cl<sub>2(g)</sub> + H<sub>2</sub>S<sub>(aq)</sub> 2HCl<sub>(aq) </sub>+ S<sub>(s)</sub></p>
<p> ;</p>
<p><strong><em>Ionic:</em></strong></p>
<p>Cl<sub>2(g)</sub> + S<sup>2-</sup><sub>(g)</sub> 2Cl<sup>&#8211;</sup><sub>(g) </sub>+ S<sub>(s)</sub></p>
<p> ;</p>
<p><strong>(b). Reaction with sodium sulphite.</strong></p>
<p><strong>Procedure:</strong></p>
<p>&#8211; Chlorine gas is bubbled through sodium sulphate in a beaker.</p>
<p>&#8211; Resulting solution is then divided into two portions.</p>
<p>&#8211; To the first portion, drops of dilute nitric acid are added followed by few drops of barium nitrate solution.</p>
<p>&#8211; To the second portion, few drops of lead (II) nitrate are added and the mixture warmed then cooled.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p><strong>1<sup>st</sup> portion</strong>: <strong>White precipitate</strong> formed indicating presence of SO<sub>4</sub><sup>2-</sup>;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Explanations:</strong></p>
<p>&#8211; The white precipitate indicate presence of SO<sub>4</sub><sup>2-</sup>; the precipitate is barium sulphate Ba(SO<sub>4</sub>)<sub>2</sub>;</p>
<p>&#8211; Chlorine oxidizes SO<sub>3</sub><sup>2-</sup> in Na<sub>2</sub>SO<sub>3</sub> to SO<sub>4</sub><sup>2-</sup> while itself is reduced to chloride ions;</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>H<sub>2</sub>O<sub>(l)</sub> + Cl<sub>2(g)</sub> + Na<sub>2</sub>SO<sub>3(aq)</sub> Na<sub>2</sub>SO<sub>4(aq)</sub> + 2HCl<sub>(aq)</sub></p>
<p> ;</p>
<p><strong>Ionically:</strong></p>
<p>Cl<sub>2(g)</sub> + SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> + H<sub>2</sub>O<sub>(l) </sub> SO<sub>4</sub><sup>2-</sup><sub>(aq)</sub> +<sup> </sup>2H<sup>+</sup><sub>(aq)</sub> + 2Cl<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; On adding barium nitrate (<strong>Ba(NO<sub>3</sub>)<sub>2</sub></strong>); the <strong>Ba<sup>2+</sup></strong> ions react with the <strong>SO<sub>4</sub><sup>2-</sup></strong><sup> </sup>to form insoluble <strong>BaSO<sub>4</sub></strong>; the white precipitate.</p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>Ba<sup>2+</sup><sub>(aq) </sub><sup> </sup>+ SO<sub>4</sub><sup>2-</sup><sub>(aq) </sub>BaSO<sub>4(s)</sub></p>
<p>(White precipitate)</p>
<p><strong>Note:</strong></p>
<p>&#8211; The solution is first acidified (with HNO<sub>3</sub>) before addition of <strong>Ba(NO<sub>3</sub>)<sub>2</sub> </strong>to prevent <strong>precipitation</strong> of<strong> BaSO<sub>3(s) </sub>and BaCO<sub>3(s).</sub></strong></p>
<p> ;</p>
<p><strong>2<sup>nd</sup> portion:</strong></p>
<p><strong>Observation:</strong></p>
<p>&#8211; Formation of a white precipitate on addition of <strong>Pb(NO<sub>3</sub>)<sub>2 </sub></strong>solution.</p>
<p>&#8211; On warming the white precipitate dissolves then recrystalizes back on cooling.</p>
<p> ;</p>
<p><strong>Explanations:</strong></p>
<p>&#8211; The white precipitate shows presence of either Cl<sup>&#8211;</sup>; SO<sub>3</sub><sup>2- </sup>or<sup> </sup>SO<sub>4</sub><sup>2-</sup></p>
<p>&#8211; However the fact that it dissolves on warming confirms the presence of Cl<sup>&#8211;</sup><sub>(aq)</sub> and not SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub> and SO<sub>3</sub><sup>2-</sup><sub>(aq)</sub></p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>Pb<sup>2+</sup><sub>(aq) </sub><sup> </sup>+ Cl<sup>&#8211;</sup><sub>(aq) </sub>PbCl<sub>2(s)</sub></p>
<p>(White precipitate soluble on warming)</p>
<p><strong> </strong></p>
<p><strong>(c). Reaction with ammonia.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>Chlorine gas is bubbled through aqueous ammonia.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p>&#8211; Evolution of <strong>white fumes</strong>.</p>
<p> ;</p>
<p><strong>(iii). Explanation.</strong></p>
<p>&#8211; Chlorine gas oxidizes ammonia to nitrogen, while is itself reduced to white fumes of ammonium chloride.</p>
<p> ;</p>
<p><strong>Equation: </strong> <strong><sub>Reduction</sub></strong></p>
<table>
<tbody>
<tr>
<td width="83"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>8NH<sub>3(g)</sub> + 3Cl<sub>2(g)</sub> 6NH<sub>4</sub>Cl<sub>(g) </sub>+ N<sub>2(s)</sub></p>
<table>
<tbody>
<tr>
<td width="11"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong><sup>Oxidation</sup></strong></p>
<p> ;</p>
<p><strong>(d). Displacement reactions with other halogens.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; Chlorine is bubbled through aqueous solutions of fluoride, bromide and iodide ions contained in separate test tubes.</p>
<p> ;</p>
<p><strong>(ii). Observations and explanations:</strong></p>
<ul>
<li><strong>With fluoride ions.</strong></li>
</ul>
<p>&#8211; No observable change or no reaction; because chlorine is a <strong>weaker oxidizing agent</strong> than fluorine.</p>
<p> ;</p>
<ul>
<li><strong>With bromide ions:</strong></li>
</ul>
<p>&#8211; If potassium bromide was used, the colourless solution turns red-brown.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; Chlorine has a higher tendency to <strong>gain electrons</strong> than bromine.</p>
<p>&#8211; It readily oxidizes bromide ions (in KBr) to form potassium chloride and bromine which immediately dissolves to make the solution <strong>red-brown</strong>.</p>
<p> ;</p>
<p><strong>Equation: </strong> <strong><sub>Reduction</sub></strong></p>
<table>
<tbody>
<tr>
<td width="78"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>2KBr<sub>(aq)</sub> + Cl<sub>2(g)</sub> 2KCl<sub>(aq) </sub>+ Br<sub>2(l)</sub></p>
<table>
<tbody>
<tr>
<td width="11"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong><sup>Oxidation </sup></strong><strong><sup>Red brown</sup></strong></p>
<p><strong>Ionically;</strong></p>
<p>2Br<sup>&#8211;</sup><sub>(aq)</sub> + Cl<sub>2(g)</sub> 2Cl<sup>&#8211;</sup><sub>(aq)</sub> + Br<sub>2(l)</sub></p>
<p> ;</p>
<p>With iodide ions.</p>
<p>&#8211; Using potassium iodide the colourless solution would turn black.</p>
<p>Reason:</p>
<p>&#8211; Chlorine has a higher tendency to gain electrons that iodine.</p>
<p>&#8211; It readily oxidizes the I<sup>&#8211;</sup> (in KI) to form iodine and potassium chloride.</p>
<p>&#8211; Iodine solid in the resulting solution makes it black.</p>
<p> ;</p>
<p><strong>Equation: </strong> <strong><sub>Reduction</sub></strong></p>
<table>
<tbody>
<tr>
<td width="74"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>2KI<sub>(aq)</sub> + Cl<sub>2(g)</sub> 2KCl<sub>(aq) </sub>+ I<sub>2(l) (black)</sub></p>
<table>
<tbody>
<tr>
<td width="16"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong><sup>Oxidation </sup></strong></p>
<p><strong>Ionically;</strong></p>
<p>2I<sup>&#8211;</sup><sub>(aq)</sub> + Cl<sub>2(g)</sub> 2l<sup>&#8211;</sup><sub>(aq)</sub> + Br<sub>2(l)</sub></p>
<p> ;</p>
<ol start="9">
<li><strong> Reaction with alkalis.</strong></li>
</ol>
<p><strong>(a). Reaction with sodium hydroxide solution.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; Bubble chlorine slowly through cold dilute sodium hydroxide solution.</p>
<p>&#8211; Dip litmus paper.</p>
<p> ;</p>
<p><strong>(ii). Observation:</strong></p>
<p>&#8211; Litmus paper is bleached; the product has the colour and smell of chlorine.</p>
<p> ;</p>
<p> ;</p>
<p><strong>(iii). Explanation:</strong></p>
<p>&#8211; Chlorine dissolves in sodium hydroxide to form a pale yellow solution of sodium chlorate (I) or sodium hypochlorite (NaClO);</p>
<p>&#8211; The sodium chlorate (I) bleaches dyes by oxidation.</p>
<p><strong>Equation:</strong></p>
<p>Cl<sub>2(g)</sub>+ 2NaOH<sub>(l)</sub> NaCl<sub>(aq)</sub> + NaClO<sub>(aq) </sub>+ H<sub>2</sub>O<sub>(l)</sub></p>
<table>
<tbody>
<tr>
<td width="191"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Pale yellow solution</p>
<p><strong>Bleaching action of NaClO:</strong></p>
<p>&#8211; The NaClO donates <strong>oxygen</strong> to the dye making it <strong>colourless</strong>; and thus it bleaches by <strong>oxidation.</strong></p>
<p><strong>Equation:</strong></p>
<p>Dye + NaClO<sub>(aq)</sub> NaCl<sub>(aq)</sub> + {Dye + [O]}</p>
<p>Coloured Colourless</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>With hot concentrated sodium hydroxide, the chlorine forms <strong>sodium chlorate (III); NaClO<sub>3</sub></strong>.</p>
<p><strong>Equation:</strong></p>
<p>3Cl<sub>2(g)</sub>+ 6NaOH<sub>(l)</sub> 5NaCl<sub>(aq)</sub> + NaClO<sub>3(aq) </sub>+ 3H<sub>2</sub>O<sub>(l)</sub></p>
<p> ;</p>
<p><strong>(b). Reaction with potassium hydroxide</strong></p>
<p>&#8211; Follows the trend of sodium.</p>
<p> ;</p>
<p><strong>(c). Reaction with slaked lime {Ca(OH)<sub>2(s)</sub>}</strong></p>
<p><strong>Equation:</strong></p>
<p>Cl<sub>2(g)</sub>+ Ca(OH)<sub>2(l)</sub> CaOCl<sub>2(aq) </sub>+ 3H<sub>2</sub>O<sub>(l)</sub></p>
<p><strong>Calcium chlorate I</strong></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>Bleaching powder, CaOCl<sub>2</sub> always smells of strongly of chlorine because it reacts with carbon (IV) oxide present in the atmosphere to form chlorine.</p>
<p><strong>Equation:</strong></p>
<p>CaOCl<sub>2(s)</sub> + CO<sub>2(g)</sub> CaCO<sub>3(s)</sub> + Cl<sub>2(g)</sub></p>
<p> ;</p>
<ol start="10">
<li><strong> Effects of chlorine gas on:</strong></li>
</ol>
<p><strong>(a). A burning candle.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; A burning candle is lowered into a gas jar of chlorine.</p>
<p> ;</p>
<p><strong>(ii). Observations:</strong></p>
<p>&#8211; It burns with a small, <strong>red</strong> and <strong>sooty flame</strong>.</p>
<p> ;</p>
<p><strong>(iii). Explanations:</strong></p>
<p>&#8211; Wax (in candles) consists of mainly hydrocarbons.</p>
<p>&#8211; The hydrogen of the hydrocarbon reacts with chlorine forming hydrogen chloride while leaving behind carbon.</p>
<p> ;</p>
<p><strong>(b). warm turpentine.</strong></p>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; A little turpentine is warmed in a dish and a filter paper soaked (dipped) in it.</p>
<p>&#8211; The filter paper is then dropped into a gas jar of chlorine.</p>
<p><strong>(ii). Observation:</strong></p>
<p>&#8211; There is a <strong>red flash</strong> accompanied by a <strong>violent action</strong> whilst a <strong>black cloud</strong> of solid particles form.</p>
<p> ;</p>
<p><strong>(iii). Conclusion:</strong></p>
<p>&#8211; Black cloud of slid is carbon.</p>
<p>&#8211; Turpentine (a hydrocarbon) consists of hydrogen and carbon combined together.</p>
<p>&#8211; The chlorine combines with hydrogen and leaves the black carbon behind.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p>C<sub>10</sub>H<sub>16(l)</sub> + 8Cl<sub>2(g)</sub> 16HCl<sub>(g)</sub> + 10C<sub>(s)</sub></p>
<p> ;</p>
<ol start="11">
<li><strong> Effects of sunlight on chlorine water.</strong></li>
</ol>
<p><strong>(i). Procedure:</strong></p>
<p>&#8211; Chlorine water is made by dissolving the gas in water.</p>
<p>&#8211; A long tube filled with chlorine water is inverted over a beaker containing water.</p>
<p>&#8211; It is then exposed to sunlight (bright light) as shown below.</p>
<p> ;</p>
<p><strong>(ii). Apparatus:</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(iii). Observations:</strong></p>
<p>&#8211; After sometime a gas collects in the tube and on applying a glowing splint, the splint is rekindles showing that the gas collected is oxygen.</p>
<p> ;</p>
<p><strong>(iv). Explanation:</strong></p>
<p>&#8211; Chlorine water has two components.</p>
<p><strong>Equation:</strong></p>
<p>Cl<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub> HCl<sub>(aq)</sub> + HOCl<sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; The HOCl being unstable will dissolve on exposure to sunlight, giving out oxygen.</p>
<p><strong>Equation:</strong></p>
<p>2HOCl<sub>(aq)</sub> 2HCl<sub>(aq)</sub> + O<sub>2(g)</sub> (slow reaction)</p>
<p> ;</p>
<p><strong>Overall reaction:</strong></p>
<p>2H<sub>2</sub>O<sub>(l)</sub> + 2Cl<sub>2(g)</sub> 4HCl<sub>(aq)</sub> + O<sub>2(g)</sub></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Industrial manufacture of chlorine (the mercury cathode cell)</strong></p>
<p><strong>The electrolysis of brine</strong></p>
<p><strong>(i). Apparatus.</strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>(ii). Electrolyte.</strong></p>
<p><strong>&#8211; Brine, </strong>concentrated sodium chloride solution, NaCl</p>
<p> ;</p>
<p><strong>(iii). Electrodes.</strong></p>
<p><strong>Anode:</strong> carbon (graphite)</p>
<p><strong>Cathode:</strong> Flowing mercury;</p>
<p> ;</p>
<p><strong>(iv). Ions present:</strong></p>
<p>NaCl<sub>(aq)</sub> Na<sup>+</sup><sub>(aq)</sub> + Cl<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p> ;</p>
<p>H<sub>2</sub>O<sub>(l) </sub> H<sup>+</sup><sub>(aq)</sub> + OH<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p><strong>(v). Reactions:</strong></p>
<p><strong>Anode:</strong></p>
<p>&#8211; Cl<sup>&#8211;</sup> and OH<sup>&#8211;</sup> migrate to the anode.</p>
<p>&#8211; Because of <strong>high concentration</strong> of Cl<sup>&#8211;</sup><sub>(aq)</sub>, they are discharged in preference to OH<sup>&#8211;</sup> ions.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2Cl<sup>&#8211;</sup><sub>(aq)</sub> Cl<sub>2(g)</sub> + 2e<sup>&#8211;</sup></p>
<p>(Green-yellow)</p>
<p> ;</p>
<p><strong>Cathode:</strong></p>
<p>&#8211; H<sup>+</sup><sub>(aq)</sub> and Na<sup>+</sup><sub>(aq)</sub> migrate to the cathode.</p>
<p>&#8211; Because the cathode is made of mercury, Na<sup>+</sup><sub>(aq)</sub> is discharged in preference to H<sup>+</sup><sub>(aq)</sub> ions;</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2Na<sup>+</sup><sub>(aq)</sub> + 2e<sup>&#8211;</sup> 2Na<sub>(s)</sub></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; Sodium formed at the cathode dissolves in the flowing mercury cathode to form <strong>sodium amalgam</strong> (Na/Hg).</p>
<p>&#8211; Sodium amalgam is reacted with water to form sodium hydroxide and hydrogen.</p>
<p>&#8211; Mercury (in the sodium amalgam) remains unreacted.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p>2Na/Hg<sub>(l)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> 2NaOH<sub>(aq)</sub> + H<sub>2(g)</sub> + 2Hg<sub>(l)</sub></p>
<p> ;</p>
<p>&#8211; The unreacted mercury is recycled.</p>
<p> ;</p>
<p><strong>(vi). Products:</strong></p>
<p>&#8211; <strong>Chlorine </strong>gas at the anode.</p>
<p>&#8211; <strong>Hydrogen </strong>and <strong>sodium hydroxide</strong> at the cathode.</p>
<p> ;</p>
<p><strong>Uses of chlorine gas and its compounds.</strong></p>
<ol>
<li>Manufacture of <strong>hydrochloric acid.</strong></li>
<li>Used in form of <strong>bleaching powder</strong> in textile and paper industries.</li>
<li>For <strong>sterilization</strong> of water for both domestic and industrial use and in swimming pools.</li>
<li>Used in <strong>sewage treatment</strong> e.g. NaOClO<sub>3</sub> solution used in latrines.</li>
<li>Manufacture of <strong>plastics</strong> (polyvinyl chloride; PVC)</li>
<li>Manufacture of <strong>germicides</strong>, pesticides and fungicides e.g. DDT and some CFCs.</li>
<li>CFCs are used to manufacture <strong>aerosol propellants</strong>.</li>
<li>Manufacture of <strong>solvents </strong>such as trichloromethane and some chlorofluorocarbons (CFCs).</li>
<li>CFCs are commonly <strong>freons</strong> are used as <strong>refrigerants</strong> in fridges and air condition units due to their low boiling points.</li>
<li>Manufacture of <strong>chloroform</strong>, an aesthetic.</li>
</ol>
<p> ;</p>
<p><strong>Hydrogen chloride gas.</strong></p>
<p><strong>Laboratory preparation of hydrogen chloride gas.</strong></p>
<p><strong>(i). Apparatus:</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure:</strong></p>
<p>&#8211; Concentrated sulphuric acid is reacted with sodium chloride, and the mixture heated gently.</p>
<p>&#8211; Resultant gas is passed through conc. Sulphuric (VI) acid; to dry the gas.</p>
<p> ;</p>
<p><strong>(iii). Equation:</strong></p>
<p>H<sub>2</sub>SO<sub>4(l)</sub> + NaCl<sub>(aq)</sub> NaHSO<sub>4(s)</sub> + HCl<sub>(g)</sub></p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>H<sup>+</sup><sub>(aq)</sub> + Cl<sup>&#8211;</sup><sub>(aq) </sub> HCl<sub>(g)</sub></p>
<p><strong>Note:</strong></p>
<p>&#8211; The reaction can proceed in the cold, but on large scale HCl(g) is produced by the same reaction but the heating is continued to re hot.</p>
<p> ;</p>
<p><strong>Properties of hydrogen chloride gas.</strong></p>
<ol>
<li>Colourless gas with a strong irritating pungent smell.</li>
<li>Slightly denser than air (1¼ times). This makes it possible to collect the gas by downward delivery.</li>
<li>Very soluble in water; and fumes strongly in moist air forming hydrochloric acid deposits.</li>
</ol>
<p><strong> </strong></p>
<p><strong>Diagram: </strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p>&#8211; The aqueous solution is known as hydrochloric acid.</p>
<p>&#8211; It is almost completely ionized (a strong acid) in aqueous solution.</p>
<p><strong>Equation:</strong></p>
<p>HCl<sub>(aq)</sub> H<sup>+</sup><sub>(aq)</sub> + Cl<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p>&#8211; This solution has the usual acidic properties:</p>
<p><strong>Examples:</strong></p>
<p>(i). turns blue litmus red.</p>
<p>(ii). Liberates hydrogen gas with certain metals e.g. zinc, Magnesium, iron etc.</p>
<p><strong>Note:</strong></p>
<p>Hydrochloric acid does not react with metals below hydrogen in the reactivity series.</p>
<p><strong>Equations:</strong></p>
<p>Zn<sub>(s)</sub> + 2HCl<sub>(aq)</sub> ZnCl<sub>2(aq)</sub> + H<sub>2(g)</sub></p>
<p>Mg<sub>(s)</sub> + 2HCl<sub>(aq)</sub> MgCl<sub>2(aq)</sub> + H<sub>2(g)</sub></p>
<p>Fe<sub>(s)</sub> + 2HCl<sub>(aq)</sub> FeCl<sub>2(aq)</sub> + H<sub>2(g)</sub></p>
<p> ;</p>
<p>(iii). Neutralizes bases to form salt and water.</p>
<p><strong>Examples:</strong></p>
<p>HCl(aq) + NaOH(aq) NaCl(aq) +H<sub>2</sub>O(l)</p>
<p>2HCl(aq) + CuO(s) CuCl<sub>2</sub>(aq) + H<sub>2</sub>O(l)</p>
<p> ;</p>
<p>(iv). Liberates carbon (IV) oxide from carbonates and hydrogen carbonates.</p>
<p><strong>Examples:</strong></p>
<p>CaCO<sub>3(s)</sub> + 2HCl<sub>(aq) </sub> CaCl<sub>2(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + CO<sub>2(g)</sub></p>
<p>ZnCO<sub>3(s)</sub> + 2HCl<sub>(aq) </sub> ZnCl<sub>2(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + CO<sub>2(g)</sub></p>
<p>NaHCO<sub>3(s)</sub> + HCl<sub>(aq) </sub> NaCl<sub>(aq)</sub> + H<sub>2</sub>O<sub>(l)</sub> + CO<sub>2(g)</sub></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Note:</strong></p>
<p>As the hydrogen chloride gas very soluble in water, the solution must be prepared using a funnel arrangement; to prevent sucking back and increase the surface area for the dissolution of the gas;</p>
<p> ;</p>
<p><strong>Diagram: dissolution of hydrogen chloride gas</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<ol start="4">
<li>Dry hydrogen chloride is NOT particularly reactive at ordinary temperatures, although very reactive metals burn in it to form the chloride and hydrogen gas.</li>
</ol>
<p>Equation:</p>
<p>2Na<sub>(s)</sub> + 2HCl<sub>(aq)</sub> 2NaCl<sub>(s)</sub> + H<sub>2(g)</sub></p>
<p> ;</p>
<p>Metals above hydrogen in the reactivity series react with hydrogen chloride gas when heated.</p>
<p><strong>Note:</strong></p>
<p>If reacted with some metals it forms 2 chlorides e.g. iron where iron (II) and iron (III) chlorides exist.</p>
<p> ;</p>
<ol start="5">
<li>Hydrogen chloride gas forms white fumes of ammonium chloride when reacted with ammonia gas;</li>
</ol>
<p>Equation:</p>
<p>NH<sub>3(g)</sub> + HCl<sub>(g)</sub> NH<sub>4</sub>Cl<sub>(s)</sub></p>
<p> ;</p>
<p><strong>Note</strong>: This is the <strong>chemical test</strong> for hydrogen chloride gas.</p>
<p> ;</p>
<ol start="6">
<li>Hydrogen chloride is decomposed by oxidizing agents, giving off chlorine.</li>
</ol>
<p>Examples:</p>
<p>PbO<sub>2(s)</sub> + 4HCl<sub>(g)</sub> PbCl<sub>2(s)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + Cl<sub>2(g)</sub></p>
<p>MnO<sub>2(s)</sub> + 4HCl<sub>(g)</sub> MnCl<sub>2(s)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> + Cl<sub>2(g)</sub></p>
<p> ;</p>
<p><strong>Diagram: reacting hydrogen chloride with an oxidizing agent.</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Test for chlorides.</strong></p>
<p><strong>Test 1: Using silver ions:</strong></p>
<p><strong>Procedure:</strong></p>
<p>&#8211; To the test solution, add silver ions from silver nitrate.</p>
<p>&#8211; Acidify with dilute nitric acid.</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Observations and inference:</strong></p>
<p>&#8211; Formation of a white precipitate shows presence of Cl<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p><strong>(iii). Explanations:</strong></p>
<p>&#8211; Only silver carbonate and silver chloride can be formed as white precipitates.</p>
<p>&#8211; Silver carbonate is soluble in dilute nitric acid but silver chloride is not.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>&#8211; Using Cl<sup>&#8211;</sup> from NaCl as the test solution;</p>
<p>NaCl<sub>(aq)</sub> + AgNO<sub>3(aq)</sub> NaNO<sub>3(aq)</sub> + AgCl<sub>(s)</sub></p>
<p>White ppt.</p>
<p> ;</p>
<p><strong>Ionically;</strong></p>
<p>Ag<sup>+</sup><sub>(aq)</sub> + Cl<sup>&#8211;</sup><sub>(aq)</sub> Ag<sub>(s)</sub></p>
<p>White ppt.</p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>&#8211; This precipitate dissolves in <strong>excess ammonia</strong>.</p>
<p>&#8211; The white precipitate of silver chloride turns <strong>violet </strong>when exposed to light.</p>
<p> ;</p>
<p><strong>Test 2: Using lead ions </strong></p>
<p><strong>(i) Procedure:</strong></p>
<p>&#8211; To the test solution, add lead ions from lead (II) nitrate, then warm</p>
<p> ;</p>
<p><strong>(ii). Observations and inference:</strong></p>
<p>&#8211; Formation of a white precipitate that dissolves on warming shows presence of Cl<sup>&#8211;</sup><sub>(aq)</sub></p>
<p> ;</p>
<p><strong>(iii). Explanations:</strong></p>
<p>&#8211; Only lead carbonate, lead sulphate, lead sulphite and lead chloride can be formed as white precipitates.</p>
<p>&#8211; Only lead chloride dissolves on warming; unlike the rest which are insoluble even on warming.</p>
<p> ;</p>
<p><strong>Equations:</strong></p>
<p>Using Cl<sup>&#8211;</sup> from NaCl as the test solution;</p>
<p>2NaCl<sub>(aq)</sub> + Pb(NO<sub>3</sub>)<sub>2(aq)</sub> 2NaNO<sub>3(aq)</sub> + PbCl<sub>2(s)</sub></p>
<p>White ppt.</p>
<p><strong>Ionically;</strong></p>
<p>Pb<sup>2+</sup><sub>(aq)</sub> + Cl<sup>&#8211;</sup><sub>(aq)</sub> PbCl<sub>2(s)</sub></p>
<p>White ppt.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Hydrochloric acid.</strong></p>
<p><strong>Large scale manufacture of hydrochloric acid.</strong></p>
<p><strong>(i). Diagram:</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Raw materials:</strong></p>
<p>&#8211; <strong>Hydrogen </strong>obtained as a byproduct of petroleum industry; electrolysis of brine or from water by <strong>Bosch process</strong>;</p>
<p>&#8211; <strong>Chlorine </strong>obtained from the electrolysis of brine or as fused calcium chloride.</p>
<p> ;</p>
<p><strong>(iii). Procedure:</strong></p>
<p>&#8211; A small sample of hydrogen gas is allowed through a jet and burnt in excess chlorine gas.</p>
<p><strong>Equation:</strong></p>
<p>H<sub>2(g)</sub> + Cl<sub>2(g)</sub> 2HCl<sub>(g)</sub></p>
<p> ;</p>
<p><strong>Precaution: </strong>A mixture of equal volumes of hydrogen and chlorine explodes when put in sunlight.</p>
<p> ;</p>
<p>&#8211; The hydrogen chloride gas formed is dissolved in water over glass beads.</p>
<p>&#8211; The <strong>glass beads</strong> <strong>increase the surface area</strong> over which absorption takes place.</p>
<p>&#8211; Commercial hydrochloric acid is about 35% pure.</p>
<p>&#8211; Hydrochloric acid is transported in steel tanks lined inside with <strong>rubber.</strong></p>
<p>&#8211; If the acid comes into contact with exposed parts of metal or with rust, it forms <strong>iron (III) chloride</strong> that makes the acid appear <strong>yellow</strong>.</p>
<p> ;</p>
<p><strong>Pollution in an industry manufacturing hydrochloric acid.</strong></p>
<p>(i). Chlorine is <strong>poisonous.</strong></p>
<p>(ii). Mixture of hydrogen and oxygen in air is <strong>explosive</strong> when ignited.</p>
<p> ;</p>
<p><strong>Uses of hydrochloric acid.</strong></p>
<ol>
<li>Sewage treatment.</li>
<li>Treatment of water (<strong>chlorination</strong>) at the waterworks.</li>
<li>Removing rust from metal e.g. descaling iron before it is galvanized or and other metals before they are electroplated.</li>
<li>Making dyes, drugs and photographic materials like <strong>silver chloride</strong> on photographic films.</li>
</ol>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Environmental pollution by chlorine and its compounds.</strong></p>
<ol>
<li>Chlorine may dissolve in rain and fall as <strong>acid rain</strong>, which has adverse effects on plants and animals, buildings and soil nutrients.</li>
<li>CFCs are <strong>non-biodegradable</strong>. Over time, they diffuse into the atmosphere breaking down to free chlorine and fluorine atoms. These atoms deplete the <strong>ozone layer</strong>. Chlorine is thus one of the <strong>greenhouse gases.</strong></li>
<li>PVCs are <strong>non-biodegradable</strong>.</li>
<li>DDT is a pesticide containing chlorine and has a long life span, affecting plants and animal life.</li>
</ol>
<p>Note: DDT is banned in Kenya; NEMA advises increased use of <strong>pyrethroids</strong> in mosquito control.</p>
<p> ;</p>
<p><strong>ORGANIC CHEMISTRY I</strong></p>
<p><strong>Contents checklist.</strong></p>
<p><strong><u> </u></strong></p>
<h2>ORGANIC CHEMISTRY</h2>
<h2>Definition</h2>
<p>&#8211; The chemistry of hydrogen carbon chain compounds.</p>
<p>&#8211; It the study of carbon compounds except the oxides of carbon i.e. CO, CO<sub>2</sub> and Carbons.</p>
<p> ;</p>
<h1>ORGANIC CHEMISTRY I: THE HYDROCARBONS</h1>
<p> ;</p>
<p><strong>Hydrocarbons</strong></p>
<p>Are compounds of hydrogen and carbon only; and are the simplest organic compounds.</p>
<p> ;</p>
<h1>Main groups of hydrocarbons</h1>
<p>Are classified on the basis of the type of bonds found within the carbon atoms.</p>
<ul>
<li><strong>Alkanes:</strong> Are hydrocarbons in which carbon atoms are linked by single covalent bonds.</li>
<li><strong>Alkenes:</strong> Carbon atoms are held by at least one double bond.</li>
<li><strong>Alkynes:</strong> Have at least one triple bond between any tow carbon atoms.</li>
</ul>
<p> ;</p>
<p><strong>Saturated and unsaturated hydrocarbons</strong></p>
<p><strong>(a). Saturated hydrocarbons</strong></p>
<p>&#8211; Are hydrocarbons which the carbon atoms are bonded to the maximum number of other atoms possible.</p>
<p>&#8211; hydrocarbons which don react and hence cannot decolourise both Bromine water and acidified potassium manganate (VII).</p>
<p>&#8211; They are compounds in which each carbon atom has only single covalent bonds, throughout the structure.</p>
<p> ;</p>
<p><strong>(b). Unsaturated hydrocarbons</strong></p>
<p>&#8211; Are hydrocarbons which contain at least one double or bond, between any two adjacent carbon atoms.</p>
<p>&#8211; The carbon atoms do not have maximum covalency.</p>
<p>&#8211; They can decolourise both bromine water and acidified potassium manganate (VII).</p>
<p> ;</p>
<p><strong>Examples:</strong> All alkenes and Alkynes.</p>
<p><strong> </strong></p>
<p><strong>Experiment: To verify saturated and unsaturated hydrocarbons.</strong></p>
<p><strong>Procedure:<br />
</strong>&#8211; 3 to 4 drops of bromine wate are added to about 1 cm3 of the liquid under investigation.</p>
<p>&#8211; The mixture is then shaken thoroughly and the observations recorded;</p>
<p>&#8211; For gases the gas under investigation is bubbled ito 1 cm3 of bromine water;</p>
<p>&#8211; The procedures are then repeated with acidified potassium manganate (VII);</p>
<p> ;</p>
<p><strong>Observations:</strong></p>
<table>
<tbody>
<tr>
<td rowspan="2" width="135"> ;</p>
<h1>COMPOUND</h1>
</td>
<td colspan="2" width="647">
<h5>OBSERVATIONS</h5>
</td>
</tr>
<tr>
<td width="323"><strong>With potassium permanganate</strong></td>
<td width="323"><strong>With Bromine water</strong></td>
</tr>
<tr>
<td width="135">Kerosene</td>
<td width="323">No observable colour change</td>
<td width="323">No colour change</td>
</tr>
<tr>
<td width="135">Laboratory gas</td>
<td width="323">No observable colour change</td>
<td width="323">No observable colour change</td>
</tr>
<tr>
<td width="135">Turpentine</td>
<td width="323">Purple colour turns colourless</td>
<td width="323">Solution is decolourised</td>
</tr>
<tr>
<td width="135">Hexane</td>
<td width="323">No observable colour change</td>
<td width="323">No observable colour change</td>
</tr>
<tr>
<td width="135">Pentene</td>
<td width="323">Potassium permanganate is decolourised</td>
<td width="323">Solution is decolourised</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>Conclusion</strong></p>
<p>&#8211; Kerosene, laboratory gas and hexane are saturate hydrocarbons</p>
<p>&#8211; Turpentine and pentane are unsaturated hydrocarbons.</p>
<p> ;</p>
<p><strong>Homologous series</strong></p>
<p>&#8211; Refers to a group of organic compounds that have the same general formula, whose consecutive members differ by a similar unit, and usually have similar chemical properties.</p>
<p> ;</p>
<p><strong>Characteristics of a Homologous series.</strong></p>
<p>(i). Can be represented by a general formula;</p>
<p>(ii). Have similar chemical properties</p>
<p>(iii). Have similar structures and names</p>
<p>(iv). They show a steady gradation of physical properties</p>
<p>(v). Can usually be prepared by similar methods.</p>
<p> ;</p>
<p><strong>Structural and molecular formula</strong></p>
<ul>
<li><strong>Molecular formulae</strong></li>
</ul>
<p>&#8211; Simply shows the number and type of elements (atoms) in the compound.</p>
<p> ;</p>
<ul>
<li><strong>Structural formula</strong></li>
</ul>
<p>Shows how the different atoms in the molecules (of a compound) are bonded or joined together.</p>
<p><strong> </strong></p>
<p><strong>Example:</strong></p>
<p><strong>Methane</strong></p>
<p>Molecular formula CH<sub>4</sub>;</p>
<p> ;</p>
<p>Structural formula</p>
<p>H</p>
<p>│</p>
<p>H – C – H</p>
<p>│</p>
<p>H</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<ol>
<li><strong> Alkanes</strong></li>
</ol>
<p>Are the simplest hydrocarbons with the general formula; C<sub>n</sub>H<sub>2n + 2</sub> where n = number of carbon atoms in the molecule.</p>
<p> ;</p>
<p><strong>Examples:</strong></p>
<p>&#8211; For compound with only 1 carbon atom, formula = CH<sub>4</sub></p>
<p>&#8211; 2 carbon atoms; the formula = C<sub>2</sub>H<sub>6</sub></p>
<p> ;</p>
<p><strong>Names and formulas of the first 10 Alkanes</strong></p>
<p> ;</p>
<p><strong>Note:</strong></p>
<p>Consecutive members of the alkane series differ by a CH<sub>2</sub>-unit, hence a <strong>homologous series</strong>.</p>
<p> ;</p>
<p><strong>(a). General formula</strong></p>
<p>&#8211; The Alkanes have a general formula C<sub>n</sub>H<sub>2n+2</sub> where n is the number of carbon atoms in the molecule.</p>
<p><strong>Example: </strong></p>
<p>When n = 3, (2n + 2) = 8, and the alkane has the formula C<sub>3</sub>H<sub>8</sub> (Propane)</p>
<p> ;</p>
<p><strong>(b). Structure</strong></p>
<p>&#8211; In all Alkanes the distribution of bonds around each carbon atom is tetrahedral.</p>
<p> ;</p>
<p><strong>Example:</strong> Methane</p>
<p><strong> </strong></p>
<p><strong>(c). Homologous series</strong></p>
<p>&#8211; The Alkanes differ from each other by a ÂCH<sub>2</sub>-.</p>
<p>&#8211; Thus methane, CH<sub>4 </sub>differs from ethane, C<sub>2</sub>H<sub>6</sub> by ÂCH<sub>2</sub>-, and ethane in turn differs from propane C<sub>3</sub>H<sub>8</sub> by  C <sub>2 </sub>-.</p>
<p>&#8211; They therefore form a homologous series.</p>
<p> ;</p>
<p><strong>(d). Functional groups</strong></p>
<p>&#8211; A functional group is a part of a compound which has a characteristic set of properties.</p>
<p>&#8211; Thus when a bromine atom replaces a hydrogen atom in an alkane, it imparts to the compound new chemical and physical properties.</p>
<p> ;</p>
<p><strong>Examples:</strong> six important functional groups.</p>
<p> ;</p>
<p><strong>(e). Isomerism</strong></p>
<p>&#8211; Is a situation whereby two or more compounds have similar molecular formulae but different structural formula.</p>
<p>&#8211; Such compounds are called <strong>isomers</strong>, i.e compounds with the same molecular formula but different structural formula.</p>
<p> ;</p>
<p><strong>Examples:</strong> For Butane, (C<sub>4</sub>H<sub>10</sub>) there are <strong>two</strong> possible structures.</p>
<p><strong> </strong></p>
<p>Isomers have different physical and chemical properties.</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>Example</strong>: Ethanol and dimethyl ether.</p>
<p>&#8211; Molecular formula: both have C<sub>2</sub>H<sub>6</sub>O</p>
<p> ;</p>
<ul>
<li><strong>Structural formula:</strong></li>
</ul>
<p>(i). Ethanol (ii). Dimethyl ether</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Differences</strong></p>
<table>
<tbody>
<tr>
<td width="420"><strong>Ethanol</strong></td>
<td width="390"><strong>Dimethyl ether</strong></td>
</tr>
<tr>
<td width="420">&#8211; A liquid of boiling point 78.4<sup>o</sup>C</p>
<p>&#8211; Completely soluble in water</p>
<p>&#8211; Reacts with sodium ethoxide and liberates hydrogen gas</td>
<td width="390">&#8211; A gas at room temperature (B.P Â 24<sup>0</sup>C).</p>
<p>&#8211; Slightly soluble in water.</p>
<p>&#8211; Does not react with sodium metal.</td>
</tr>
</tbody>
</table>
<p><strong> </strong></p>
<p><strong>(f). Alkyl groups</strong></p>
<p>&#8211; Is a group formed by the removal of a hydrogen atom form a hydrocarbon.</p>
<p>&#8211; Alkyl groups donÂt exist on their own but are always attached to another atom or group.</p>
<p><strong><em> </em></strong></p>
<p><strong>Naming of alkyl groups</strong></p>
<p>&#8211; Is done by removing the ending -ane from the parent alkane and replacing it with Âyl.</p>
<p><strong> </strong></p>
<p><strong>Examples</strong></p>
<p>Methane (CH<sub>4</sub>) gives rise to Methyl -CH<sub>3</sub></p>
<p>Ethane (C<sub>2</sub>H<sub>6</sub>) gives rise to ethyl, &#8211; C<sub>2</sub>H<sub>5 </sub>i.e. -CH<sub>2</sub>CH<sub>3</sub></p>
<p>Propane (C<sub>3</sub>H<sub>8</sub>) gives rise to Propyl, &#8211; C<sub>3</sub>H<sub>7</sub> // -CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub>;</p>
<p><strong> </strong></p>
<p><strong>(g). Nomenclature of Alkanes</strong></p>
<p>&#8211; Generally all Alkanes end with the suffix -ane;</p>
<p>&#8211; Alkanes can either be <strong>straight chain</strong> or <strong>branched</strong>.</p>
<p> ;</p>
<p><strong>(i). Straight chain Alkanes</strong></p>
<p>&#8211; The names of all Alkanes end with the suffix -ane;</p>
<p><strong>Examples: </strong></p>
<p>Methane, ethane, propane, butane.</p>
<p> ;</p>
<p>&#8211; With the exception of the first 4 members of the series (i.e. the 4 listed above) the names of Alkanes begin with a Greek prefix indicating the number of carbon atoms in the main chain.</p>
<p>Examples: &#8211; Pentane  5 carbon atoms</p>
<p>Hexane  6 carbon atoms.</p>
<p> ;</p>
<p><strong>(ii). Branched Alkanes</strong></p>
<p>The naming of branched chain Alkanes is based on the following rules:-</p>
<ol>
<li>The largest continuous chain of carbon atoms in the molecule is used to deduce the parent name of the compound.</li>
<li>The carbon atoms of this chain are numbered such that the branching // substituents are attached to the carbon atom bearing the lowest number.</li>
<li>The substituent // branch is named e.g. methyl, ethyl etc and the name of the compound written as <strong>one word.</strong></li>
</ol>
<p> ;</p>
<p><strong>Examples</strong></p>
<p>Further examples</p>
<p>H H H CH<sub>2</sub>CH<sub>2</sub>CHCH<sub>2</sub>CH<sub>3</sub></p>
<p>│ │ │ │ │</p>
<p>H – C – C – C – H CH<sub>3</sub> CH<sub>2</sub></p>
<p>│ │</p>
<p>H – C – H CH<sub>3</sub></p>
<p>│ 3-ethylhexane;</p>
<p>H</p>
<p>2-methylpropane;</p>
<p> ;</p>
<p><strong>Further examples.</strong></p>
<ol>
<li>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>3</sub></li>
</ol>
<p>│</p>
<p>CH<sub>3</sub></p>
<p>3-methylpentane;</p>
<p> ;</p>
<ol start="2">
<li>CH<sub>3</sub></li>
</ol>
<p>│</p>
<p>H<sub>3</sub>C – C – CH<sub>3</sub></p>
<p>│</p>
<p>CH<sub>3</sub></p>
<p>2, 2-dimethylpropane;</p>
<p> ;</p>
<p><strong>Note:</strong> refer to course books and draw as many examples as possible.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Draw the structural isomers of:</strong></p>
<ol>
<li><strong> Butane.</strong></li>
</ol>
<p><strong> </strong></p>
<ol start="2">
<li><strong> Pentane;</strong></li>
</ol>
<p><strong> </strong></p>
<ol start="3">
<li><strong> Hexane;</strong></li>
</ol>
<p><strong> </strong></p>
<p><strong>(f). Occurrence of Alkanes</strong></p>
<p>&#8211; There are 3 known natural sources:</p>
<p><strong>(i). Natural gas:</strong> this consists of mainly of methane;</p>
<p> ;</p>
<p><strong>(ii). Crude oil:</strong></p>
<p>&#8211; Consists of a mixture of many Alkanes</p>
<p>&#8211; It can be separated into its components by fractional distillation.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; The different components have different boiling points.</p>
<p> ;</p>
<p><strong>(iii). Biogas:</strong> This contains about 60-75% of methane gas/marshy gas.</p>
<p> ;</p>
<p><strong>Separation of the components of crude oil.</strong></p>
<p><strong>(i). Apparatus</strong></p>
<p><strong> </strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>(ii). Procedure</strong></p>
<p>&#8211; The apparatus is arranged as shown above.</p>
<p>&#8211; The first distillate appears at about 120<sup>o</sup>C and is collected, the of 40<sup>o</sup>C intervals thereafter until the temperatures reach 350<sup>o</sup>C.</p>
<p> ;</p>
<p><strong>(iii). Observations and explanations</strong></p>
<p>&#8211; This method of separation is called fractional distillation, and depends on the fact that the various components of the mixture have <strong>different boiling points</strong>.</p>
<p>&#8211; The various fractions vary in properties as explained below.</p>
<p> ;</p>
<p><strong>(a). Appearance</strong></p>
<p>&#8211; Intensity of the colour increases with increase in boiling point.</p>
<p>&#8211; Boiling point increases with increasing number of carbon atoms.</p>
<p><strong>Reason: </strong></p>
<p>&#8211; The higher the number of carbon atoms, the higher the number of <strong>covalent bonds</strong>.</p>
<p>&#8211; Thus the first fraction to be distilled (lab gas) is colourless while the last distillates (between) is dark black in colour.</p>
<p> ;</p>
<p><strong>(b). Viscosity</strong></p>
<p>&#8211; <strong>Increases</strong> with increasing <strong>boiling point</strong>;</p>
<p>&#8211; The fractions with low boiling points are less viscous while the fraction with the highest boiling point is semi-solid;</p>
<p> ;</p>
<p><strong>(c). Inflammability:</strong></p>
<p>&#8211; Decreases with increasing boiling points.</p>
<p>&#8211; The gaseous fractions, with least boiling points readily catches fire // burn, while the semi-solid fractions with very high boiling points are almost non-combustible.</p>
<p> ;</p>
<p><strong>Note:</strong> Some Hydrocarbons are found in more than one fraction of crude oil and more advanced chemical methods are necessary for complete separation.</p>
<p> ;</p>
<p><strong>Uses of the various fractions of crude oil.</strong></p>
<table>
<tbody>
<tr>
<td width="255"><strong>No. f carbon atom per molecule</strong></td>
<td width="165"><strong>Fractions</strong></td>
<td width="375"><strong>Uses</strong></td>
</tr>
<tr>
<td width="255">1-4</td>
<td width="165">Gases</td>
<td width="375">Laboratory gases and gas cookers</td>
</tr>
<tr>
<td width="255">5-12</td>
<td width="165">Petrol</td>
<td width="375">Fuel in petrol engines</td>
</tr>
<tr>
<td width="255">9-16</td>
<td width="165">Kerosene (paraffin)</td>
<td width="375">Fuel for jet engines (aeroplanes) and domestic uses</td>
</tr>
<tr>
<td width="255">15-18</td>
<td width="165">Light diesel oils</td>
<td width="375">Fuel for heavy diesel engines e.g. for ships</td>
</tr>
<tr>
<td width="255">18-25</td>
<td width="165">Diesel oils</td>
<td width="375">Fuel for diesel engines</td>
</tr>
<tr>
<td width="255">20-70</td>
<td width="165">Lubricating oils</td>
<td width="375">Used for smooth running of engine parts</td>
</tr>
<tr>
<td width="255">>;70</td>
<td width="165">Bitumen</td>
<td width="375">Road tarmacking</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>Changes // gradation of physical properties across the alkane homologous series</strong></p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="120"><strong>Name of alkane</strong></td>
<td width="90"><strong>Formula</strong></td>
<td width="202"><strong>State of room temperature (208K)</strong></td>
<td width="53"><strong>M.P (K)</strong></td>
<td width="60"><strong>B.P (K)</strong></td>
<td width="82"><strong>Density</strong></p>
<p><strong>(g cm<sup>-3</sup>)</strong></td>
<td width="94"><strong>Solubility</strong></td>
<td width="94"><strong>Solubility</strong></td>
</tr>
<tr>
<td width="120">Methane</p>
<p>Ethane</p>
<p>Propane</p>
<p>Butane</p>
<p>Pentane</p>
<p>Hexane</p>
<p>Heptane</p>
<p>Octane;</p>
<p>Nonane</p>
<p>Decane</td>
<td width="90">CH<sub>4</sub></p>
<p>C<sub>2</sub>H<sub>6</sub></p>
<p>C<sub>3</sub>H<sub>8</sub></p>
<p>C<sub>4</sub>H<sub>10</sub></p>
<p>C<sub>5</sub>H<sub>12</sub></p>
<p>C<sub>6</sub>H<sub>14</sub></p>
<p>C<sub>7</sub>H<sub>16</sub></p>
<p>C<sub>8</sub>H<sub>10</sub></p>
<p>C<sub>9</sub>H<sub>20</sub></p>
<p>C<sub>10</sub>H<sub>22</sub></td>
<td width="202">↑</p>
<p> ;</p>
<p>Gaseous</p>
<p>↓</p>
<p>↑</p>
<p> ;</p>
<p>Liquid</p>
<p> ;</p>
<p> ;</p>
<p>↓</td>
<td width="53">90</p>
<p>91</p>
<p>85</p>
<p>138</p>
<p>143</p>
<p>178</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p>243</td>
<td width="60">112</p>
<p>184</p>
<p>231</p>
<p>273</p>
<p>309</p>
<p>342</p>
<p>447</td>
<td width="82">0.424</p>
<p>0.546</p>
<p>0.582</p>
<p>0.579</p>
<p>0.626</p>
<p>0.659</p>
<p>0.730</td>
<td width="94"> ;</td>
<td width="94"> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>Preparation and chemical properties of Alkanes</strong></p>
<p><strong>Note:</strong></p>
<p>&#8211; Alkanes, like any other Homologous series have similar chemical properties.</p>
<p>&#8211; Generally any alkane can be represented form the reaction represented by the following equation:</p>
<p><strong>C<sub>n</sub>H<sub>2n + 1</sub>COONa + NaOH<sub>(aq)</sub> → C<sub>n</sub>H<sub>2n +2</sub> + Na<sub>2</sub>CO<sub>3(aq)</sub>;</strong></p>
<p><strong> </strong></p>
<p><strong>Thus;</strong></p>
<p>&#8211; Methane can be prepared form sodium ethanoate (CH<sub>3</sub>COONa)</p>
<p>&#8211; Ethane can be prepared form sodium propanoate (CH<sub>3</sub>CH<sub>2</sub>COONa)</p>
<p>&#8211; Propane can be prepared form sodium Butanoate (CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>COONa)</p>
<p><strong>Laboratory Preparation of methane</strong></p>
<p><strong>(i). Apparatus</strong></p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong> </strong></p>
<p><strong>(ii). Procedure</strong></p>
<p>&#8211; About 5g of odium ethanoate and an equal mass of soda lime is put in a hard glass test tube, upon mixing them thoroughly in a mortar.</p>
<p>&#8211; The mixture is heated thoroughly in the test-tube.</p>
<p> ;</p>
<p><strong>(iii). Observation</strong></p>
<p>&#8211; A colourless gas collects over water</p>
<p><strong>Reasons:</strong></p>
<p>&#8211; Methane does not react with and is insoluble in water.</p>
<p> ;</p>
<p><strong>Equation</strong></p>
<p>CH<sub>3</sub>COONa + NaOH<sub>(s)</sub> → CH<sub>4(g)</sub> + Na<sub>2</sub>CO<sub>3(aq)</sub></p>
<p><strong><em>Sodium ethanoate sodalime Methane Sodium carbonate</em></strong></p>
<p> ;</p>
<p><strong>Physical properties of methane</strong></p>
<ol>
<li>It is a non-poisonous, colourless gas.</li>
<li>It is slightly soluble in water, but quite soluble in organic solvents such as ethanol and ether.</li>
<li>II is less denser than air and when cooled under pressure, it liquefies.</li>
</ol>
<p> ;</p>
<p><strong>Chemical properties</strong></p>
<ol start="4">
<li><strong> Burning </strong></li>
</ol>
<p>&#8211; It is flammable and burns in excess air // oxygen with a pale blue non-luminous flame to give carbon (IV) oxide ad water vapour.</p>
<p><strong>Equation:</strong></p>
<p>CH<sub>4(g)</sub> + 2O<sub>2(g)</sub> → CO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(g)</sub></p>
<p><strong> </strong></p>
<p><strong>Note:</strong> In a limited supply of air, the flame is <strong>luminous</strong>.</p>
<p><strong>Reason:</strong></p>
<p>&#8211; This is due to incomplete combustion of the methane.</p>
<p>&#8211; A mixture of methane and air <strong>explodes</strong> violently when ignited if the volume ratio is approximately 1:10 and this is often the cause of fatal explosions in coal mines.</p>
<p> ;</p>
<ol start="5">
<li><strong>Reaction with Bromine water and acidified potassium permanganate</strong></li>
</ol>
<p>&#8211; When methane is bubbled through bromine water the red brown colour of bromine persists; and when bubbled through acidified potassium manganate (VII) solution; the purple colour of the solution remains;</p>
<p>&#8211; Thus it has no effect on either bromine water or acidified potassium permanganate.</p>
<p><strong>Reason:</strong> It is a saturated hydrocarbon.</p>
<p> ;</p>
<ol start="6">
<li><strong> Substitution reactions</strong></li>
</ol>
<p>&#8211; A substitution reaction is one in which one atom replaces another atom in a molecule.</p>
<p><strong> </strong></p>
<p><strong>Example: The substitution of Bromine in methane.</strong></p>
<p><strong>Procedure:</strong></p>
<p>&#8211; A sample of Methane (CH<sub>4</sub>) is placed in a boiling tube and to it is added some bromine gas.</p>
<p>&#8211; The tube is stoppered, and the mixture shaken, then allowed to stand and exposed to <strong>ultra-violet lamp.</strong></p>
<p> ;</p>
<p><strong>Observations </strong></p>
<p>&#8211; The red colour of Bromine begins to fade, and the pungent smell of hydrogen bromide (HBr) gas is detectable when the stopper is removed.</p>
<p>&#8211; A moist blue litmus paper also turns <strong>red</strong> on dipping into the resultant mixture.</p>
<p><strong>Equation </strong>CH<sub>4(g)</sub> + Br<sub>2(g)</sub> → CH<sub>3</sub>Br<sub>(g)</sub> + HBr<sub>(g)</sub></p>
<p><strong>Explanation &#8211; </strong>For a chemical reaction to occur, bonds must be broken.<strong> &#8211; </strong>The light energy (V.V. light) splits the Bromine molecule into free atoms, which are very reactive species.<strong> &#8211; </strong>Similarly the energy breaks the weaker carbon  hydrogen bonds, and not the stronger carbon  carbon bonds.<strong> &#8211; </strong>The free bromine atoms can then substitute (replace one of the hydrogen atoms of methane, resulting unto bromomethane and hydrogen bromide gas.</p>
<p><strong>Note:</strong> This process can be repeated until all hydrogen atoms in CH<sub>4</sub> are replaced.</p>
<p><em>Write all the equations to show the stepwise substitution of all hydrogen atoms in methane.</em></p>
<p>&#8211; The substitution reactions can also occur with chlorine, forming chloremethane dichloromethane, trichloromethane (chloroform) and tetrachloromethane (carbon tetrachloride) respectively.</p>
<p><strong>Equations:</strong></p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Uses of methane &#8211; </strong>It is used as a fuel &#8211; Used in the manufacture of carbon black which is used in printers ink and paints.<strong> &#8211; </strong>Used in the manufacture of methanol, methanal, chloromethane and ammonia.</p>
<p><strong>Cracking of Alkanes &#8211; </strong>Is the breaking of large alkane molecules into smaller Alkanes, alkenes and often hydrogen. It occurs under elevated temperatures of about 400-700<sup>o</sup>C</p>
<p><strong>Equation</strong></p>
<p><strong>Example: Cracking of propane</strong></p>
<p> ;</p>
<ol start="2">
<li><strong> Alkenes</strong></li>
</ol>
<p>&#8211; Are hydrocarbons with at least one carbon-carbon double bond, and have the general formula C<sub>n</sub>H<sub>2n</sub>.</p>
<p>&#8211; They thus form a homologous series  with the simplest member behind ethane.</p>
<p> ;</p>
<p><strong>Names and formulae of the first six alkenes.</strong></p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="212">Name of alkene</td>
<td width="165">Formula</td>
</tr>
<tr>
<td width="212">Ethene</p>
<p>Propane</p>
<p>Pbut-l-ene</p>
<p>Pent-lene</p>
<p>Hex-tene</td>
<td width="165"> ;</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p><strong>NOMENCLATURE OF ALKENES</strong></p>
<p><strong> </strong></p>
<p><strong>Rules </strong></p>
<ol>
<li>The parent molecule is the longest carbon chain; and its prefix is followed by the suffix Âene.</li>
<li>The carbon atoms in the chain are numbered such that the carbon atoms joined by the double bonds get the lowest possible numbers.</li>
<li>The position of the substituent groups is indicated by showing the position of the carbon atom to which they are attached.</li>
<li>In case of 2 double bonds in an alkene molecule, the carbon atom to which each double bond is attached must be identified.</li>
</ol>
<p> ;</p>
<p><strong>Examples</strong></p>
<p><strong> </strong></p>
<p><strong><em>Questions:</em></strong> For each of the following alkenes, draw the structural formula</p>
<p> ;</p>
<ol>
<li>Hex- l  ene</li>
<li>Prop-l-ene</li>
</ol>
<ul>
<li>Hex-2-ene</li>
</ul>
<p> ;</p>
<ol>
<li>Give the IUPAC names for:</li>
</ol>
<p><strong> </strong></p>
<p><strong>Note: Branched alkenes:</strong></p>
<p> ;</p>
<p>Event for branched alkenes, the numbering of the longest carbon chain is done such that the carbon atoms joined by the double bonds gets the smallest numbers possible.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Isomerism in alkenes</strong></p>
<ul>
<li>Alkenes show two types of isomerism:-</li>
</ul>
<ol>
<li>Branching isomerism</li>
<li>Positional isomerism</li>
</ol>
<p> ;</p>
<ol>
<li>i) Branching isomerism</li>
</ol>
<p>Occurs when a substitutent groups is attached to one of the carbon atoms in the largest chain containing the double bond.</p>
<p> ;</p>
<p><strong>Positional isomerism; in alkenes</strong></p>
<p> ;</p>
<p>Is a situation whereby two or more unsaturated alkenes have same molecular formular but different structural formula; due to alteration of the position of the double bond.</p>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<p><strong>Question:</strong> Draw all the possible isomers of Hexene , resulting from positional and branching isomerism.</p>
<p> ;</p>
<p>Gradation of physical properties of Alkenes</p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="152">Name of alkene</td>
<td width="112">Formula</td>
<td width="132">(MP<sup>0</sup>C)</td>
<td width="101">B.P (0)</td>
<td width="162">Density g/cm<sup>3</sup></td>
<td width="132">solubility</td>
</tr>
<tr>
<td width="152">Ethene</p>
<p>Propene</p>
<p>But-l-ene</p>
<p>Pent-l-ene</p>
<p>Hex-l-ene</td>
<td width="112"> ;</td>
<td width="132">-169</p>
<p>-189</p>
<p>-185</p>
<p>-138</p>
<p>-98</td>
<td width="101">-104</p>
<p>&#8211;47.7</p>
<p>-6.2</p>
<p>-3.0</p>
<p>-98</td>
<td width="162">&#8211;</p>
<p>&#8211;</p>
<p>&#8211;</p>
<p>0.640</p>
<p>0.674</td>
<td width="132"> ;</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p>Note: the double bond is the reactive site in alkenes</p>
<p> ;</p>
<p><strong>Preparation and chemical properties of Ethene</strong></p>
<p> ;</p>
<ol>
<li>i) <strong><em>Apparatus</em></strong></li>
</ol>
<p> ;</p>
<p> ;</p>
<ol>
<li><strong><em>Procedure</em></strong></li>
</ol>
<p>A mixture of ethanol and concentrated sulfuric acid in the ratio 1:2 respectively are heated in a flask to a temp. of 160<sup>0</sup>C Â 180<sup>0</sup>C.</p>
<p> ;</p>
<ul>
<li><strong><em>Observation</em></strong></li>
</ul>
<p>A colourless gas results; and is collected over water.</p>
<p> ;</p>
<p>Reasons: Its insoluble, unreactive and lighter than water.</p>
<p> ;</p>
<ol>
<li><em>Equation</em></li>
</ol>
<p> ;</p>
<ol>
<li><em>Explanation</em></li>
</ol>
<p> ;</p>
<p>At 160<sup>0</sup>C Â 180<sup>0</sup>C the conc. H2SO4 dehydrates the ethanol, removing a water molecule form it and the remaining C and H atoms rearrange and combine to form Ethene which is collected as colourless gas.</p>
<p> ;</p>
<p><strong>Note:</strong> At temperature below 140<sup>0</sup>C, a different compound called ether is predominantly formed.</p>
<p> ;</p>
<p>Ethene can also be prepared by passing hot aluminum oxide over ethanol. The later of which acts as a catalyst i.e.</p>
<p> ;</p>
<p><strong><u>Reactions of ethene/chemical properties</u></strong></p>
<p> ;</p>
<ol>
<li>Burning/combustion</li>
</ol>
<p>Just like an alkenes and alkanes, ethene burn in air, producing carbon dioxide and large quantities of heat.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p><strong> </strong></p>
<p><strong>Caution:</strong> Mixtures of air and ethene can be explosive and must be handled very carefully.</p>
<p> ;</p>
<ol>
<li><strong>Additional reactions:</strong></li>
</ol>
<p>Is a reaction in which are molecule adds to another to form a single product occur in alkenes due to presence of a double bond.</p>
<p> ;</p>
<ol>
<li><strong>With oxidizing agents </strong></li>
<li>i) Reaction with acidified potassium permanganate.</li>
</ol>
<p><strong><em>Procedure</em></strong>: Ethene is bubbled into a test tube containing acidified potassium <strong><em> permanganate.</em></strong></p>
<p><strong><em>Observation</em></strong>: The purple colour of the solution disappears.</p>
<p><strong><em>Explanation:</em></strong> Ethene reduces the potassium permanganate.</p>
<p>The permanganate ion is reduced to Manganese (II) ion and water.</p>
<p> ;</p>
<p><strong><u>Equation</u></strong></p>
<p> ;</p>
<p><strong>Note</strong>: The net effect of the above reaction is the addition of two ÂOH groups to the double bond forming ethan-1, 2-dio(ethylene glycol).</p>
<p>In cold countries ethylene glycol is used as an antifreeze in car radiators.</p>
<p> ;</p>
<ol>
<li>Reaction with acidified potassium chromate (VI) (K2Cr2O7)</li>
</ol>
<p> ;</p>
<ol start="2">
<li>Halogenations is the addition of halogen atoms across a double bond.</li>
<li>i) Reaction with Bromine Br2(g)</li>
</ol>
<p><strong> </strong></p>
<p><strong>Procedure:</strong> Ethene is mixed with Bromine liquid/gas</p>
<p><strong>Observation:</strong> The reddish brown bromine gas is decoloursed/becomes colourless.</p>
<p><strong>Explanation:</strong> Bromine is decoloursed due to the addition of Bromine atoms to the twocarbon atoms f the double bond forming 1.2 dibromethane.</p>
<p> ;</p>
<ol>
<li><strong>ii) Reaction with chlorine</strong></li>
</ol>
<p>The Chlorine (greenish yellow) also gets decoloursied due the addition of its atoms on the double bond.</p>
<p> ;</p>
<p><strong> </strong></p>
<p><strong>Note:</strong> Alkenes react with and decolourise halogens and potassium permanganate by additional reaction at room temperature and pressure.</p>
<p> ;</p>
<p>The reaction site is the double bond and hence/all alkenes will react in a similar manner.</p>
<p><strong>Example;</strong> Butene and Bromine</p>
<p> ;</p>
<p> ;</p>
<p>iii) Reaction with Bromine water</p>
<p>Bromine is dissolved in water and reacted with ethene.</p>
<p> ;</p>
<p><strong>Equation:</strong></p>
<p> ;</p>
<p>Further examples of additional reactions</p>
<p> ;</p>
<ol start="3">
<li>Addition of hydrogen halides</li>
</ol>
<p> ;</p>
<ol>
<li>With hydrobromic acid; HBr (aq)</li>
</ol>
<p> ;</p>
<p><strong><em><u>With sulphuric acid</u></em></strong></p>
<p> ;</p>
<ol start="4">
<li>Addition of Ethene with sulphuric acid</li>
</ol>
<p><strong> </strong></p>
<p><strong>Note:</strong> When ethylhydrogen sulphate is hydrolysed, ethanol is formed.</p>
<p> ;</p>
<p>In this reaction, water is added to ehylhydrogen sulphate and the mixture warmed.</p>
<p> ;</p>
<ol start="5">
<li>Ethene with Hydrogen i.e. Hydrogenation.</li>
</ol>
<p> ;</p>
<p>Is commonly termed hydrogenation though just a typical addition reaction.</p>
<p> ;</p>
<p>Ethene is reacted with hydrogen, under special conditions.</p>
<p><strong> </strong></p>
<p><strong>Conditions;</strong> moderate temperature and pressure.</p>
<p>Nickel catalyst/palladure catalyst.</p>
<p><strong> </strong></p>
<p><strong>Equation:</strong></p>
<p> ;</p>
<p><strong>Application</strong>: it is used industrially in the conversion f various oils into fats e.g. in the preparation of Margarine.</p>
<p> ;</p>
<ol start="6">
<li><strong>Polymerization reactions.</strong></li>
</ol>
<p>Also called self-addition reactions</p>
<p>Alkanes have the ability to link together (polymerise) to though the double bond to give a molecule of larger molecular mass (polymers)</p>
<p> ;</p>
<p><strong>Polymers:</strong> Are very large molecules formed when 2 or more (smaller) molecules link together to form a larger unit.</p>
<p>Polymers have properties different form those of the original constituent manners.</p>
<p> ;</p>
<p><strong>Examples:</strong> Polymerisation of ethene</p>
<p> ;</p>
<ol>
<li><strong>i) Conditions</strong></li>
</ol>
<ul>
<li>High temperatures of about 200<sup>0</sup>C</li>
<li>High/elevated pressures of approximately 1000 atmospheres</li>
<li>A trace of oxygen catalyst.</li>
</ul>
<p> ;</p>
<ol>
<li><strong>ii) Procedure:</strong> Ethene is heated at 200<sup>0</sup>C and 1000 atm. Pressure over a catalyst.</li>
</ol>
<p> ;</p>
<p><strong>iii) Observation:</strong> Sticky white substance which hardens on cooling is formed. This solid is called polythene, commonly reffered to as polythene.</p>
<p> ;</p>
<ol>
<li><strong>Equation:</strong></li>
</ol>
<p> ;</p>
<p> ;</p>
<p><strong><u>Generally</u></strong></p>
<p> ;</p>
<p><strong><u>Uses of polythene</u></strong></p>
<p> ;</p>
<ol>
<li>Used for the manufacture of many domestic articles (bowls, buckets, water cans, and cold water pipes) e.t.c.</li>
</ol>
<p><strong> </strong></p>
<p><strong>Note:</strong> Polythene pipes have a great advantage over metal pipes as they can be welded quickly and do not burst in frosty weather.</p>
<p> ;</p>
<ol start="2">
<li>Manufacture of reagent bottles, droppers, stoppers etc. since polythene is unaffected by alkalis and acids.</li>
</ol>
<p> ;</p>
<p><strong><u>Test for Alkenes</u></strong></p>
<p><strong><u> </u></strong></p>
<p>&#8211; They decolourise bromine water, acidified potassium manganate VII.</p>
<p>i.e. These addition reactions show the presence of a double bond.</p>
<p> ;</p>
<p><strong><u>Uses of Alkenes</u></strong></p>
<p> ;</p>
<ol>
<li>Manufacture of plastics, through polymerization.</li>
<li>Manufacture of ethanol; through hydrolysis reactions</li>
<li>Ripening of fruits.</li>
<li>Manufacture of ethan  1, 2-diol(glyco) which is used as a coolant.</li>
</ol>
<p> ;</p>
<p><strong> </strong></p>
<ol start="3">
<li><strong>ALYKYNES</strong></li>
</ol>
<p><strong> </strong></p>
<p>Are unsaturated hydrocarbons which form a homologous series of a general formula CnH2n-2, where n = 2 or more.</p>
<p> ;</p>
<p>The functional groups of the alkyne series is the carbon  carbon tripple bond.</p>
<p> ;</p>
<p>They also undergo addition reactions because of High unsaturation and may be polymerised like the alkenes.</p>
<p><strong><u> </u></strong></p>
<p><strong><u>Examples</u></strong></p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="177"><strong>Name</strong></td>
<td width="198"><strong>Molecular formula</strong></td>
<td width="210"><strong>Structural formular</strong></td>
</tr>
<tr>
<td width="177">Ethyne</p>
<p>Propyne</p>
<p>But-l-yne</p>
<p>Pent-l-yne</td>
<td width="198">C2H2</p>
<p>C3H4</p>
<p>C4H6</p>
<p>C5H8</td>
<td width="210">CH CH</p>
<p>CH3C CH</p>
<p>CH3CH2C CH</p>
<p>CH3(CH2)2C CH</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p><strong>Nomenclature of alkynes</strong></p>
<p><strong> </strong></p>
<ul>
<li>The largest chain with the tripple carbon  carbon bond forms the parent molecule.</li>
<li>Numbering of the carbon atoms is done such that the carbon atom with the tripple bond acquires the lowest possible number.</li>
<li>The substituent branch if any is named, and the compound written as a single word.</li>
<li></li>
</ul>
<p><strong>Examples</strong></p>
<p> ;</p>
<p> ;</p>
<ol start="2">
<li>Draw the structures of the following hydrocarbons</li>
<li>2,2 dimethyl-but-2-yne</li>
<li>propyne</li>
</ol>
<ul>
<li>4,4 diethyl-hex-2-yne.</li>
</ul>
<p> ;</p>
<p><strong>Isomerism in alkynes</strong></p>
<p><strong> </strong></p>
<ol>
<li><strong>Positional isomerism</strong></li>
</ol>
<p>Isomerism commonly occurs in alkynes due to the fact that the position of the tripple bond can be altered.</p>
<p> ;</p>
<p>Such isomers, as usual have same molecular but different structural formulas.</p>
<p> ;</p>
<p><strong>Examples </strong></p>
<ol>
<li>i) Isomers of Butyne</li>
</ol>
<p> ;</p>
<ol>
<li></li>
</ol>
<p> ;</p>
<ol>
<li>Branching isomerism  occurs when alkyl group is present in the molecule.</li>
</ol>
<p> ;</p>
<ol>
<li>Others</li>
</ol>
<p> ;</p>
<p><strong><u>Gradation in physical properties of Alkynes</u></strong></p>
<p> ;</p>
<table>
<tbody>
<tr>
<td width="182">Name of Alkyne</td>
<td width="210">Formula</td>
<td width="128">M.P/<sup>0</sup>C</td>
<td width="105">B.P/<sup>0</sup>C</td>
<td width="143">Density/gcm-3</td>
</tr>
<tr>
<td width="182">Ethyne</p>
<p>Propyne</p>
<p>Butyne</p>
<p>Pent-l-yne</p>
<p>Hex-l-yne</td>
<td width="210">HC CH</p>
<p>CH3 CH</p>
<p>CH3CH2CC CH</p>
<p>CH3CH2CH2C CH</p>
<p>CH3(CH2)3C CH</td>
<td width="128">-8108</p>
<p>-103</p>
<p>-122</p>
<p>-90</p>
<p>-132</td>
<td width="105">-83.6</p>
<p>-23.2</p>
<p>8.1</p>
<p>39.3</p>
<p>71</td>
<td width="143">&#8211;</p>
<p>&#8211;</p>
<p>&#8211;</p>
<p>0.695</p>
<p>0.716</td>
</tr>
</tbody>
</table>
<p> ;</p>
<p> ;</p>
<p>Preparation and chemical properties of Ethyne.</p>
<p> ;</p>
<ol>
<li>Preparation</li>
<li>i) Apparatus</li>
</ol>
<p> ;</p>
<p> ;</p>
<p> ;</p>
<ol>
<li><strong>ii) Procedure: </strong></li>
</ol>
<p>Water is dripped over calcium carbide and is collected over water.</p>
<p>Reasons for over-water collection:-</p>
<ul>
<li>ItÂs insoluble in water</li>
<li>Unreactive and lighter than water.</li>
</ul>
<p> ;</p>
<ul>
<li><strong>Conditions</strong></li>
<li>Room temperature</li>
</ul>
<p> ;</p>
<ol>
<li><strong>Equation</strong></li>
</ol>
<p> ;</p>
<p> ;</p>
<ol>
<li><strong>Properties of Ethyne</strong></li>
<li><strong><em>i) Physical</em></strong></li>
</ol>
<ul>
<li>Colourless gas, with a sweet smell when pure.</li>
<li>Insoluble in water and can thus be collected over water.</li>
<li>Solubility is higher in non- solvents * Draw table on physical properties.</li>
</ul>
<ol>
<li><strong><em>Chemical properties</em></strong></li>
</ol>
<ul>
<li>Combustion</li>
</ul>
<p>Ethyne burns with a luminous and very sooty flame; due to the high percentage of carbon content, some of which remains unburnt.</p>
<ul>
<li>In excess air, the products are carbon dioxide and water.</li>
</ul>
<p> ;</p>
<p><strong>Equation</strong></p>
<p> ;</p>
<p>In limited air, they undergoes incomplete combustion, forming a mixture of carbon and carbon dioxide.</p>
<p> ;</p>
<p><strong>Note:</strong> A sooty flame observed when a hydrocarbon burns in air is an indication of unsaturation in the hydrocarbon.</p>
<p> ;</p>
<p><strong>Addition reactions</strong></p>
<p>During addition reactions of alkynes (Ethyne) the tripple bond breaks in stages;</p>
<p> ;</p>
<ol>
<li>Reaction with hydrogen (Hydrogenation)</li>
</ol>
<p> ;</p>
<p> ;</p>
<p><strong>Note: </strong>This reaction occurs under special conditions i.e. &#8211; Presence of a Nickel catalyst</p>
<p>Temperatures about 200<sup>0</sup>C</p>
<p> ;</p>
<ol>
<li>Reaction with halogens</li>
<li>i) Reaction with chlorine</li>
</ol>
<p> ;</p>
<p> ;</p>
<ol>
<li><strong>With Bromine gas </strong></li>
</ol>
<ul>
<li>The red-brown bromine vapour is decoloursed.</li>
</ul>
<p> ;</p>
<p><strong>Equations</strong></p>
<p> ;</p>
<p>Note: In this reaction Cl2 should be diluted with an inert.</p>
<p> ;</p>
<p>Reason: Pure Cl2 reacts explosively with Ethyne, forming carbon and HCl.</p>
<p> ;</p>
<ol>
<li><strong>Reaction with Bromine liquid</strong></li>
</ol>
<p>When Ethyne reacts with Bromine water, the reddish  brown colour of bromine water disappears.</p>
<p> ;</p>
<p><strong>Reason:</strong> The Bromine adds to the carbon tripple bond leading to the   of 1;1,2,2 tetrabromoethane.</p>
<p> ;</p>
<p><strong>Equation</strong></p>
<p> ;</p>
<p>E; Ethyne also decolorizes acidified potassium permanganate.</p>
<p> ;</p>
<p><strong>Note:</strong> Decolourization of acidified potassium permanganate and bromine water are tests for unsaturated hydrocarbons (alkanes and alkynes)</p>
<p> ;</p>
<ol>
<li><strong>Reaction with hydrogen halides</strong></li>
</ol>
<p> ;</p>
<p><strong>Uses of Ethyne</strong></p>
<ol>
<li>Industrial manufacture of compounds like adhesives and plastics</li>
<li>ItÂs used in the oxy-acetylene flame which is used for welding and cutting metals.</li>
</ol>

