FORM 2 CHEMISTRY EXAMS PLUS MARKING SCHEMES

Name: ……………………………………………………                Adm. No.: …………….

Stream: …………………………………………………….            Date: ……………………

233/1

Form II – Chemistry

Kenya Certificate of Secondary Education (K.C.S.E.) 

Chemistry

2 Hours

Instructions to Students

• Write your name and admission number in the spaces provided above
• Write the date of examination in the spaces provided above.
• Answer all the questions in this question paper
• Mathematical tables and silent electronic calculators may be used
• All working MUST be clearly shown where necessary
• This paper consists of 10 printed pages
• Students should check the question paper to ascertain that all the pages are printed as indicated and that no questions are missing

For Official Use Only

Questions	Maximum Score	Candidate’s Score
1-29	80

 

1. Give two reasons why non-luminous flame is used in school laboratories. (2marks)

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….

2. Using kinetic theory explain the difference between solid and liquid   (2marks)

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….……

 

3. Name the most suitable method of separation that can be used to separate:

(a) Oil from cashew nut                                                                                                            (1mark)

………………………………………………………………………………………………………….

 

1. b) Sodium chloride from a solution of potassium chloride and sodium chloride mixture

…………………………………………………………………………………………………….. (1mark)

 

4. The diagram below shows oxygen can be prepared in a laboratory. Study it and answer the questions that follow.

1. a) Name the liquid X (1mark)

 

…………………………………………………………………………………………………….

 

1. b) Write a balance chemical equation to shows how oxygen is produced in the boiling tube. (1mark)

 

 

1. c) Give one industrial use of oxygen (1mark)

 

.…………………………………………………………………………………………………………

 

5. Metal Xreacts with cold water slowly while Y does react with neither cold water nor hot water. Metal Z react with both cold water and hot water vigorously and explosively respectively.
6. Arrange these metals in order of increasing reactivity                                                        (1mark)

 

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….

 

1. b) Chlorine was passed through solution of iodide of X.Give one observation. That can be made. (1mark)

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….

1. c) Explain the observation made in (b) above (1mark)

.…………………………………………………………………………………………………………

 

6. The diagram below represents a paper chromatogram for three brands of juices suspected to contain banned food colourings

	K                              L                            M

 

The results showed the presence of banned food colorings in L and M only. On the same diagram

• Circle the spots which show banned food colouring (1mark)
• Indicate the solvent front (1mark)
• Give one application of chromatography.                                                                (1mark)

.…………………………………………………………………………………………………………

 

7. The diagram below represents a set up that was used to show that part of air is used during burning.
8. a) Given that phosphorus used was in excess, draw a diagram of the set up at the end of

the experiment (When there was no further observable change)                              (1mk)

1. b) Suggest one modification that should be made on the apparatus if the percentage of the air used is to be determined. (1mk)

……………………………………………………………………………………………

……………………………………………………………………………………………

8. The set up below represents the apparatus that may be used to separate a mixture of

Two  miscible liquids C and D whose boiling points are 80⁰C and 110⁰C.

 

 

1. a) Name B                                                                                                                        (1mk)

……………………………………………………………………………………………

1. b) What is the purpose of the thermometer?             (1mk)

 

……………………………………………………………………………………………

 

1. c) Which liquid was collected in the test tube?                                                                   (1mk)

 

9. The relative atomic mass of R is 10.28. It has two isotopes. Calculate the relative

Percentage abundance of each isotope                                                                                (3mks)

 

 

 

 

 

 

10. Identify the following apparatus stating their uses in the laboratory

 

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

11. A mixture contains sodium chloride, Ammonium chloride, and copper (II) Oxide. Describe how each of the substance can be obtained from the mixture                                                (3mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

12. The PH of a sample of soil was found to be 5.0. An agricultural officer recommended the addition of calcium oxide in the soil. State two functions of the calcium oxide in the soil.                       (2mks)

 

 

 

 

13. The set –up below was used to study some properties of air.

 

 

State and explain two observations that would be made at the end of the experiment. (3mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

14. Name any two gases when mixed with oxygen can be used in welding. (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

15. State two reasons why hydrogen is not commonly used as a fuel. (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

 

 

16. An ion of phosphorous can be represented as 31. Draw a diagram to show the distribution of the electrons and the composition of the nucleus of the ion of phosphorous.                (3mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

17. Study the information in the table and answer the questions that follow.

 

Ion	Electronic arrangement	Ionic radius.
Na+	2.8	0.095
Mg2+	2.8	0.065
K+	2.8.8	0.133

 

Explain why

(i)    The ionic radius of K⁺ is greater than that of Na⁺                                                     (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

(ii) The ionic radius of Mg²⁺ is smaller than that of Na⁺                                                        (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

18. The electronic configuration of ions X²⁺ and Y^– are 2.8.8 and 2.8.8respectively.

(a) Write the electron arrangement of the element

X……………………………………………………………………………………………

Y ……………………………………………………………………………………………

(b) Write the formula of the compound that would be  formed between phosphate radical and            X.                                                                                                 (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

 

 

 

 

19    The following table shows the PH values of solutions A,B,C and D.

 

 

 

 

1. a) Which solution is likely to be that of aluminium chloride?                                  (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………

1. b) Which solution has the highest concentration of hydroxide? Explain (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………

20    Study the experiment below and answer the questions that follow. The gas produced ignites spontaneously

 

 

 

1. i) Which metal is used above (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………….

1. ii) Write down a chemical equation for the reaction demonstrated above (1mk)

………………………………………………………………………………………………………………………………………………………………………………………………

iii) What will be the colour of phenolphthalein indicator in the resulting solution?                 (1mk)

………………………………………………………………………………………………

21. In an experiment, two pieces of iron sheets were wrapped in each case with zinc and copper metal sheets as shown below. They were left in the open for some months.

 

iron

 

 

zinc                                                                   copper

(I)                                                                        (II)

 

 

State and explain the observations made in the experiments;                                   (3mk)

• ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
• ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

22. Differentiate between the terms atomic number and mass number (2mks)

…………………………………………………………………………………………………………………

…………………………………………………………………………………………………………………

……………………………………………………………………………………………………………………

 

23. Two similar gas jars were filled with carbon IV oxide. One of the gas jars was inverted over

water and the other over solution Q.

(a)            Give the possible identity of solution Q                                                              (1 mk)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

(b)            Explain the difference in heights of the liquids in the gas jars                              (2mks)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

 

24. An element W has atomic number of 9 and element F has an electronic configuration of 2.8 .7

(a)             State oxidation state of element W                                                                     (½mk)

……………………………………………………………………………………………………….

(b) How does reaction of W compare with that of F? Explain                                  (1½mks)

……………………………………………………………………………………………………….

 

 

 

25. Elements X and Y have the atomic masses of 39 and 23 respectively.

(a)             Complete the table below by filling the blank spaces                                           (1 mk)

Elements	X	Y
Atomic mass	39	23
Number of neutrons	20	12
Electronic configuration

 

 

(b)           Which element has higher ionization energy?                                                     (1 mk)

 

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

 

(c)             Explain your answer in (b) above.                                                                      (2mks)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

 

26. Element A and B with atomic numbers 12 and 17 respectively react together.

(a) Write the electronic configurations of each.

 

A ________________________________________________________    (1 mark)

 

B ________________________________________________________    (1 mark)

 

 

• Write the formula of the compound formed between A and B.

 

 

27. Study the table below and use it to answer the questions that follow.

 

 

 

Solution	PH
A	3.5
B	14
C	8.5

 

(i) In which of the solution will phenolphthalein indicator be colourless.                  (1 mark)

 

 

(ii) Which of the solutions could be used to relieve heartburn?  Explain.                    (2 marks)

 

 

28. The diagram below show the reaction of heated Magnesium with steam. Study it and answer the questions that follow.

 

 

1. a) Identify gas Z. ( ½ mk)

………………………………………………………………………………………………………

 

1. b) State why t he gas is collected as shown in the diagram. (1mk)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

1. c) State and explain the observation made in the boiling tube at the end of the experiment.

(1 ½ mks)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

1. d) Write a chemical equation for the reaction that occurs in the boiling tube.               (1mk)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

 

 

29. The diagram below shows how acidic and basic oxides fit into the general family of oxides. Study it and answer the questions that follow.

 

 

1. a) State the name given to the type of oxides that would be placed in the area labeled:-

(i)            M………………………………………………………………………….( ½ mk)

(ii)           R……………………………………………………………………………( ½ mk)

 

1. b) Give two examples of oxide that belong to M. (1mk)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

1. c) State an important property of the oxides that belong to M. (1mk)

………………………………………………………………………………………………………

……………………………………………………………………………………………………

 

 

 

 

 

 

 

MARINDI SECONDARY

FORM II

MID TERM II 2019

MARKING SCHEME

 

1. – Clean/does not produce soot

• Strong/has high heat content

2. Solid –particles are fixed /not moving/vibrates at their fixed position and are close/parked

 

Liquid –Particles are moving/constant motion and far apart/not close not packed

 

3. a) solvent extraction

b).fractional crystallization

 

MnO2

1. a) Hydrogen peroxide
2. b) 2H₂O_2(aq) 2H₂0_(l) +O_{2 (g)}

 

Balance with correct state units

Balance with wrong/missing units

1. c) – welding

– Purification of iron

 

5. a) Z, X, Y must be correct in order
6. b) Solution turned red brown.
7. c) Iodine was displaced

 

Solvent front

K                          L                     M

1. Quality control in food industry

-Separate and detect contaminants in some food/soil.

Used in pharmaceutical industries,

Finding drug compounds in urine or other body fluids

7.	a)   b) Graduating the gas jar ü1
8.	a) – Luminous flame has four distinct region while non-luminous flame has three regions – Luminous flame is bright yellow/sooty while non-luminous flame is pale blue/non sooty. – Luminous flame is large and weavy while luminous flame is short and steady – Luminous flame is fairly hot while non-luminous is very hot (Each for 1mk maximum 2)
	b) Incomplete combustion of the gas leaves hot white carbon particles which absorb light and later remit it in form of yellow light. ü1
9.	Let abundance y    be x (100 – x) ü ½ 10x + 11(100 – x) = 10.28 ü 1 100 10x + 1,100 – 11x = 1028 ü ½ X = 72 % is 72% ü ½ (100 – 72) = 28%
10.	i) Deflagrating spoon ü ½ Lowering and holding burning substances ü in the gas jars for observations ii) Dessicator ü ½ Keeping substances free from moisture in the laboratory ü

 

12. Heat the mixture ammonia chloride sublime and is collected as a sublimate leaving sodium chloride and copper (II) oxide

Add water to the mixture and stir . Filter to obtain copper (II) oxide as the residue and sodium             chloride solution as the filtrate. Evaporate the filtrate to saturation to obtain crystals of sodium             chloride.

 

13. -Iron raise the soil PH

-It provides nutrients to the plants

 

14. Iron wool turns brown or rust due to formation of hydrated iron (III) oxide.

-Level of water inside the tube rises to occupy the space left by oxygen.

 

15. -Hydrogen

-Acetylene /ethyne

 

16. -A mixture of hydrogen and air explodes when ignited.

-Hydrogen is not readily available .

 

17. -Outermost energy level shown only

 

 

 

 

18. (i) K⁺ has three energy levels white Na⁺ has only two.

(ii)        Mg²⁺ nucleus has 12 protons attract 10e^–, while Na+ has 11 protons attracting 10e^–,                                    hence Mg²⁺ radius shrinks more.

 

19. (a) X – 2.8.8.2

Y-   2.8.6

(b)        X₃(PO₄)₂

20        The following table shows the PH values of solutions A,B,C and D.

 

 

 

 

 

1. a) Which solution is likely to be that of alluminium chloride? (1mk)

AP1

1. b) Which solution has the highest concentration of hydroxide? Explain           (1mk)

DP ½ It is a strong alkali/baseP ½

 

21        Study the experiment below and answer the questions that follow. The gas produced ignites spontaneously

 

 

 

 

1. i) Which metal is used above                                                                             (1mk)

PotassiumP1

1. ii) Write down a chemical equation for the reaction demonstrated above         (1mk)

K_(s)+2H₂O_(l)→2KOH_(aq)+H_2(g) P1

iii)        What will be the colour of phenolphthalein indicator in the resulting solution?       (1mk)

PinkP

 

22. In an experiment, two pieces of iron sheets were wrapped in each case with zinc and copper metal sheets as shown below. They were left in the open for some months.

 

iron

 

 

zinc                                                                   copper

(I)                                                                        (II)

State and explain the observations made in the experiments;                                   (3mk)

• No rusting. Zinc is above iron in the reactivity series
• Rusting occurs. Iron is more reactive than copper

 

23. Differentiate between the terms atomic number and mass number (2mks)

• Atomic number – number of protons

Mass number- protons + neutrons

24.  (a)       Sodium hydroxide ü/ Potassium hydroxide ü¹/₂

 

(b)        Carbon IV Oxide is very soluble in solution Q hence the liquid rises ü to occupy partial                         vacuum left while Carbon IV Oxide is only slightly soluble in water hence little rise in

water level. ü

 

 

 

25. (a) 0ü

(b)       W is more reactive than F; ü

W has a smaller atomic size hence stronger attraction for the incoming electrons than F

 

26. . (a) X                                 Y

2.8.8.1                         2.8.1

 

(b)        Y

 

(c)        It has a smaller atomic radius than X and stronger nuclear attraction for outermost energy                         level electrons that makes electron loss more require more energy.

1. (a) A          2, 8, 2   (1mk)

B          2, 8, 7   (1mk)

 

(b)        AB₂      (1mk)

27. (i) A         (1mk)

(ii)        C (1mk) it is weakly alkaline hence will neutralize excess acid in the stomach. (1mk)

 

28. a) Hydrogen/ H_2(g)
29. b) It is less dense/ lighter than air.
30. c) –           White solid seen in the boiling tube

–           Magnesium reacts with steam forming white magnesium oxide.

1. d)

 

29. a) (i)         Amphoteric oxides

(ii)        Neutral oxides

1. b)                                Any 2 x ½ mk/ Accept correct names
2. c) They have both acidic and basic properties.               (Accept w.t.t.e)

---

---

---

Name: ……………………………………………………                Adm. No.: …………….

Stream: …………………………………………………….            Date: ……………………

 

233/1

Form II – Chemistry

June 2019

2 Hours

 

MARINDI SECONDARY SCHOOL

Kenya Certificate of Secondary Education (K.C.S.E.)

 

Chemistry

2 Hours

 

 

Instructions to Students

• Write your name and admission number in the spaces provided above
• Write the date of examination in the spaces provided above.
• Answer all the questions in this question paper
• Mathematical tables and silent electronic calculators may be used
• All working MUST be clearly shown where necessary
• This paper consists of 10 printed pages
• Students should check the question paper to ascertain that all the pages are printed as indicated and that no questions are missing

For Official Use Only

Questions	Maximum Score	Candidate’s Score
1-29	80

 

 

1. Give two reasons why non-luminous flame is used in school laboratories. (2marks)

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….

2. Using kinetic theory explain the difference between solid and liquid   (2marks)

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….……

 

3. Name the most suitable method of separation that can be used to separate:

(a) Oil from cashew nut                                                                                                            (1mark)

………………………………………………………………………………………………………….

 

1. b) Sodium chloride from a solution of potassium chloride and sodium chloride mixture

…………………………………………………………………………………………………….. (1mark)

 

4. The diagram below shows oxygen can be prepared in a laboratory. Study it and answer the questions that follow.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1. a) Name the liquid X (1mark)

 

…………………………………………………………………………………………………….

 

1. b) Write a balance chemical equation to shows how oxygen is produced in the boiling tube. (1mark)

 

 

1. c) Give one industrial use of oxygen (1mark)

 

.…………………………………………………………………………………………………………

 

5. Metal Xreacts with cold water slowly while Y does react with neither cold water nor hot water. Metal Z react with both cold water and hot water vigorously and explosively respectively.
6. Arrange these metals in order of increasing reactivity                                                        (1mark)

 

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….

 

1. b) Chlorine was passed through solution of iodide of X.Give one observation. That can be made. (1mark)

.…………………………………………………………………………………………………………

………………………………………………………………………………………………………….

1. c) Explain the observation made in (b) above (1mark)

.…………………………………………………………………………………………………………

 

6. The diagram below represents a paper chromatogram for three brands of juices suspected to contain banned food colourings

 

 

 

	K                              L                            M

 

 

 

 

 

 

 

The results showed the presence of banned food colorings in L and M only. On the same diagram

• Circle the spots which show banned food colouring (1mark)
• Indicate the solvent front (1mark)
• Give one application of chromatography.                                                                (1mark)

.…………………………………………………………………………………………………………

 

7. The diagram below represents a set up that was used to show that part of air is used during burning.
8. a) Given that phosphorus used was in excess, draw a diagram of the set up at the end of

the experiment (When there was no further observable change)                              (1mk)

 

 

 

 

 

1. b) Suggest one modification that should be made on the apparatus if the percentage of the air used is to be determined. (1mk)

……………………………………………………………………………………………

……………………………………………………………………………………………

8. The set up below represents the apparatus that may be used to separate a mixture of

Two  miscible liquids C and D whose boiling points are 80⁰C and 110⁰C.

 

 

1. a) Name B                                                                                                                        (1mk)

……………………………………………………………………………………………

1. b) What is the purpose of the thermometer?             (1mk)

 

……………………………………………………………………………………………

 

1. c) Which liquid was collected in the test tube?                                                                   (1mk)

 

9. The relative atomic mass of R is 10.28. It has two isotopes. Calculate the relative

Percentage abundance of each isotope                                                                                (3mks)

 

 

 

 

 

 

10. Identify the following apparatus stating their uses in the laboratory

 

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

11. A mixture contains sodium chloride, Ammonium chloride, and copper (II) Oxide. Describe how each of the substance can be obtained from the mixture                                                (3mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

12. The PH of a sample of soil was found to be 5.0. An agricultural officer recommended the addition of calcium oxide in the soil. State two functions of the calcium oxide in the soil.                       (2mks)

 

 

 

 

13. The set –up below was used to study some properties of air.

 

 

State and explain two observations that would be made at the end of the experiment. (3mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

14. Name any two gases when mixed with oxygen can be used in welding. (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

15. State two reasons why hydrogen is not commonly used as a fuel. (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

 

 

16. An ion of phosphorous can be represented as 31. Draw a diagram to show the distribution of the electrons and the composition of the nucleus of the ion of phosphorous.                (3mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

17. Study the information in the table and answer the questions that follow.

 

Ion	Electronic arrangement	Ionic radius.
Na+	2.8	0.095
Mg2+	2.8	0.065
K+	2.8.8	0.133

 

Explain why

(i)    The ionic radius of K⁺ is greater than that of Na⁺                                                     (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

(ii) The ionic radius of Mg²⁺ is smaller than that of Na⁺                                                        (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

18. The electronic configuration of ions X²⁺ and Y^– are 2.8.8 and 2.8.8respectively.

(a) Write the electron arrangement of the element

X……………………………………………………………………………………………

Y ……………………………………………………………………………………………

(b) Write the formula of the compound that would be  formed between phosphate radical and            X.                                                                                                 (2mks)

……………………………………………………………………………………………………….  ……………………………………………………………………………………………………….

 

 

 

 

 

19    The following table shows the PH values of solutions A,B,C and D.

 

 

 

 

1. a) Which solution is likely to be that of aluminium chloride?                                  (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………

1. b) Which solution has the highest concentration of hydroxide? Explain (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………

20    Study the experiment below and answer the questions that follow. The gas produced ignites spontaneously

 

 

 

1. i) Which metal is used above (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………….

1. ii) Write down a chemical equation for the reaction demonstrated above (1mk)

………………………………………………………………………………………………………………………………………………………………………………………………

iii) What will be the colour of phenolphthalein indicator in the resulting solution?                 (1mk)

………………………………………………………………………………………………

21. In an experiment, two pieces of iron sheets were wrapped in each case with zinc and copper metal sheets as shown below. They were left in the open for some months.

 

iron

 

 

zinc                                                                   copper

(I)                                                                        (II)

 

 

State and explain the observations made in the experiments;                                   (3mk)

• ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
• ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

22. Differentiate between the terms atomic number and mass number (2mks)

…………………………………………………………………………………………………………………

…………………………………………………………………………………………………………………

……………………………………………………………………………………………………………………

 

23. Two similar gas jars were filled with carbon IV oxide. One of the gas jars was inverted over

water and the other over solution Q.

(a)            Give the possible identity of solution Q                                                              (1 mk)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

(b)            Explain the difference in heights of the liquids in the gas jars                              (2mks)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

 

24. An element W has atomic number of 9 and element F has an electronic configuration of 2.8 .7

(a)             State oxidation state of element W                                                                     (½mk)

……………………………………………………………………………………………………….

(b) How does reaction of W compare with that of F? Explain                                  (1½mks)

……………………………………………………………………………………………………….

 

 

 

25. Elements X and Y have the atomic masses of 39 and 23 respectively.

(a)             Complete the table below by filling the blank spaces                                           (1 mk)

Elements	X	Y
Atomic mass	39	23
Number of neutrons	20	12
Electronic configuration

 

 

(b)           Which element has higher ionization energy?                                                     (1 mk)

 

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

 

(c)             Explain your answer in (b) above.                                                                      (2mks)

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

……………………………………………………………………………………………………….

 

26. Element A and B with atomic numbers 12 and 17 respectively react together.

(a) Write the electronic configurations of each.

 

A ________________________________________________________    (1 mark)

 

B ________________________________________________________    (1 mark)

 

 

• Write the formula of the compound formed between A and B.

 

 

27. Study the table below and use it to answer the questions that follow.

 

 

 

Solution	PH
A	3.5
B	14
C	8.5

 

(i) In which of the solution will phenolphthalein indicator be colourless.                  (1 mark)

 

 

(ii) Which of the solutions could be used to relieve heartburn?  Explain.                    (2 marks)

 

 

28. The diagram below show the reaction of heated Magnesium with steam. Study it and answer the questions that follow.

 

 

1. a) Identify gas Z. ( ½ mk)

………………………………………………………………………………………………………

 

1. b) State why t he gas is collected as shown in the diagram. (1mk)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

1. c) State and explain the observation made in the boiling tube at the end of the experiment.

(1 ½ mks)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

1. d) Write a chemical equation for the reaction that occurs in the boiling tube.               (1mk)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

 

 

29. The diagram below shows how acidic and basic oxides fit into the general family of oxides. Study it and answer the questions that follow.

 

 

1. a) State the name given to the type of oxides that would be placed in the area labeled:-

(i)            M………………………………………………………………………….( ½ mk)

(ii)           R……………………………………………………………………………( ½ mk)

 

1. b) Give two examples of oxide that belong to M. (1mk)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

1. c) State an important property of the oxides that belong to M. (1mk)

………………………………………………………………………………………………………

……………………………………………………………………………………………………

---

---

---

MARKING SCHEME

1. – Clean/does not produce soot

• Strong/has high heat content

2. Solid –particles are fixed /not moving/vibrates at their fixed position and are close/parked

 

Liquid –Particles are moving/constant motion and far apart/not close not packed

 

3. a) solvent extraction

b).fractional crystallization

 

MnO2

1. a) Hydrogen peroxide
2. b) 2H₂O_2(aq) 2H₂0_(l) +O_{2 (g)}

 

Balance with correct state units

Balance with wrong/missing units

1. c) – welding

– Purification of iron

 

5. a) Z, X, Y must be correct in order
6. b) Solution turned red brown.
7. c) Iodine was displaced

 

Solvent front

K                          L                     M

1. Quality control in food industry

-Separate and detect contaminants in some food/soil.

Used in pharmaceutical industries,

Finding drug compounds in urine or other body fluids

7.	a)   b) Graduating the gas jar ü1
8.	a) – Luminous flame has four distinct region while non-luminous flame has three regions – Luminous flame is bright yellow/sooty while non-luminous flame is pale blue/non sooty. – Luminous flame is large and weavy while luminous flame is short and steady – Luminous flame is fairly hot while non-luminous is very hot (Each for 1mk maximum 2)
	b) Incomplete combustion of the gas leaves hot white carbon particles which absorb light and later remit it in form of yellow light. ü1
9.	Let abundance y    be x (100 – x) ü ½ 10x + 11(100 – x) = 10.28 ü 1 100 10x + 1,100 – 11x = 1028 ü ½ X = 72 % is 72% ü ½ (100 – 72) = 28%
10.	i) Deflagrating spoon ü ½ Lowering and holding burning substances ü in the gas jars for observations ii) Dessicator ü ½ Keeping substances free from moisture in the laboratory ü

 

12. Heat the mixture ammonia chloride sublime and is collected as a sublimate leaving sodium chloride and copper (II) oxide

Add water to the mixture and stir . Filter to obtain copper (II) oxide as the residue and sodium             chloride solution as the filtrate. Evaporate the filtrate to saturation to obtain crystals of sodium             chloride.

 

13. -Iron raise the soil PH

-It provides nutrients to the plants

 

14. Iron wool turns brown or rust due to formation of hydrated iron (III) oxide.

-Level of water inside the tube rises to occupy the space left by oxygen.

 

15. -Hydrogen

-Acetylene /ethyne

 

16. -A mixture of hydrogen and air explodes when ignited.

-Hydrogen is not readily available .

 

17. -Outermost energy level shown only

 

 

 

 

18. (i) K⁺ has three energy levels white Na⁺ has only two.

(ii)        Mg²⁺ nucleus has 12 protons attract 10e^–, while Na+ has 11 protons attracting 10e^–,                                    hence Mg²⁺ radius shrinks more.

 

19. (a) X – 2.8.8.2

Y-   2.8.6

(b)        X₃(PO₄)₂

20        The following table shows the PH values of solutions A,B,C and D.

 

 

 

 

 

1. a) Which solution is likely to be that of alluminium chloride? (1mk)

AP1

1. b) Which solution has the highest concentration of hydroxide? Explain           (1mk)

DP ½ It is a strong alkali/baseP ½

 

21        Study the experiment below and answer the questions that follow. The gas produced ignites spontaneously

 

 

 

 

1. i) Which metal is used above                                                                             (1mk)

PotassiumP1

1. ii) Write down a chemical equation for the reaction demonstrated above         (1mk)

K_(s)+2H₂O_(l)→2KOH_(aq)+H_2(g) P1

iii)        What will be the colour of phenolphthalein indicator in the resulting solution?       (1mk)

PinkP

 

22. In an experiment, two pieces of iron sheets were wrapped in each case with zinc and copper metal sheets as shown below. They were left in the open for some months.

 

iron

 

 

zinc                                                                   copper

(I)                                                                        (II)

State and explain the observations made in the experiments;                                   (3mk)

• No rusting. Zinc is above iron in the reactivity series
• Rusting occurs. Iron is more reactive than copper

 

23. Differentiate between the terms atomic number and mass number (2mks)

• Atomic number – number of protons

Mass number- protons + neutrons

24.  (a)       Sodium hydroxide ü/ Potassium hydroxide ü¹/₂

 

(b)        Carbon IV Oxide is very soluble in solution Q hence the liquid rises ü to occupy partial                         vacuum left while Carbon IV Oxide is only slightly soluble in water hence little rise in

water level. ü

 

 

 

25. (a) 0ü

(b)       W is more reactive than F; ü

W has a smaller atomic size hence stronger attraction for the incoming electrons than F

 

26. . (a) X                                 Y

2.8.8.1                         2.8.1

 

(b)        Y

 

(c)        It has a smaller atomic radius than X and stronger nuclear attraction for outermost energy                         level electrons that makes electron loss more require more energy.

1. (a) A          2, 8, 2   (1mk)

B          2, 8, 7   (1mk)

 

(b)        AB₂      (1mk)

27. (i) A         (1mk)

(ii)        C (1mk) it is weakly alkaline hence will neutralize excess acid in the stomach. (1mk)

 

28. a) Hydrogen/ H_2(g)
29. b) It is less dense/ lighter than air.
30. c) –           White solid seen in the boiling tube

–           Magnesium reacts with steam forming white magnesium oxide.

1. d)

 

29. a) (i)         Amphoteric oxides

(ii)        Neutral oxides

1. b)                                Any 2 x ½ mk/ Accept correct names
2. c) They have both acidic and basic properties.               (Accept w.t.t.e)