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NAME………………………………………………………................ INDEX NO……………………...…

SCHOOL ………………………………………………. CANDIDATE’S SIGNATURE….……………

DATE………..…………………………………

233/2

CHEMISTRY

PAPER 2

(THEORY)

JUNE 2014

2 HOURS

COMA JOINT EXAM 2014

Kenya Certificate of Secondary Education

CHEMISTRY

PAPER 2

(THEORY)

2 HOURS

Instructions to candidates:

Write your Name and Index number and School in the spaces provided above.

Sign and write the date of examination in the spaces provided above.

Answer ALL the questions in the spaces provided in the question paper.

Mathematical tables and electronic calculators may be used.

All working must be shown clearly.

For Examiner’s Use Only

Questions Maximum Score Candidate’s Score

1 13

2 13

3 12

4 10

5 11

6 11

7 10

Total Score 80


Chemistry Paper 2 Turnover

1. The grid below represents part of the periodic table. The letters are not the actual symbols of the

elements. Use it to answer the questions that follow.

A

N C

R E Q M K P

J

T L

(a) (i) Name the family to which element E belong in the periodic table. (1 mark)

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(ii) State one use of element R. (1 mark)

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(b) Write equations for the reactions between:

(i) Q and N. (1 mark)

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(ii) Chloride of M and water. (1 mark)

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(c) Select an element in period three which has the smallest atomic size. Give a reason for your

answer. (2 marks)

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(d) Explain why the boiling point of M (2,680C) is higher than that of K (281C). (2 marks)

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Chemistry Paper 2 2

(e) Compare the PH of the aqueous solutions formed when oxides of R and E are dissolved in

water. Explain. (2 marks)

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(f) Select the least reactive element in group VII. Explain. (2 marks)

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(g) Select an element in group VIII which is likely to form a fluoride. (1 mark)

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2. The flow chart below shows some chemical reactions.

Compound X Ethanol CH3CH2OH

E CH3CH2COOH

CH3COOH CH3COOK

C CH2 = CH2

CH4 D Br2(g)

K(S)

Cl2(g)

Step (i)

Step (ii)

Step (iii)

B H2

CH2 – CH2 n A


(a) Write the name and formula of the organic compounds

X: (1 mark)

Name _____________________________________________________________________

Formula ___________________________________________________________________

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Chemistry Paper 2 3

C: (1 mark)

Name _____________________________________________________________________

Formula ___________________________________________________________________

___________________________________________________________________________

B: (1 mark)

Name _____________________________________________________________________

Formula ___________________________________________________________________

___________________________________________________________________________

(b) Write the name of the process that leads to the formation of substance(s).

D _____________________________________________________________ (1 mark)

A _____________________________________________________________ (1 mark)

C _____________________________________________________________ (1 mark)

(c) Give one necessary condition for the formation of compound X. (1 mark)

___________________________________________________________________________

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(d) If the relative molecular mass of compound A is 84,000 units, determine the value of n.

(C = 12, O = 1.0). (2 marks)


(e) Write an equation for the reaction leading to the formation of substance(s) E. (1 mark)

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___________________________________________________________________________

(f) State and explain the observation made when substances “B” and C2H4 are burnt in excess

air. (2 marks)

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Chemistry Paper 2 4

3. I Study the scheme below and answer the questions that follow.

(a) State the sources of the substance X and Y. (2 marks)

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(b) Identify the catalyst used in step I and how it is made to be effective. (1 mark)

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(c) Name the substance A, B, C and E. (2 marks)

Y X

Salt F Ammonia Solid A Gas B

Dilute

H2SO4

CuO

Step III

Brown gas D

Colourless gas E

Substance C Cu(NO3)2 Heat Cu(S)

Step IV

Step II O2/H2O/catalyst

Catalyst

Step I


A __________________________________________________________________

B __________________________________________________________________

C __________________________________________________________________

E __________________________________________________________________

(d) Write the chemical equations that shows:

(i) The formation of substance C. (1 mark)

_______________________________________________________________

_______________________________________________________________

(ii) The reaction between substance C and copper metal. (1 mark)

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(e) State one economic use of substance F. (1 mark)

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Chemistry Paper 2 5

II Below is a set-up in the preparation of a particular salt. Study it and answer the questions

that follow.

(a) Explain the observation made in the combustion tube when dry hydrogen chloride

gas is passed instead of dry chlorine. (2 marks)

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(b) Identify solid K. (1 mark)

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(c) What property makes solid K to be collected in the flask as shown above? (1 mark)

Dry chlorine gas

Heat

Iron wool

Anhydrous calcium chloride

Solid K


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4. Study the given diagram and answer the questions that follow:

(a) Name A and C. (1 mark)

A _________________________________________________________________________

C _________________________________________________________________________

(b) (i) Give one element that is the most appropriate to be used a electrodes. (1 mark)

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Chemistry Paper 2 6

(ii) Explain your answer in b(i) (1 mark)

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(c) (i) Comment on the concentration of the electrolyte at the end of the experiment. (1 mark)

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(ii) Explain your answer in c(i). (1 mark)

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(d) (i) Arrange the following anions in the order of increasing ease of discharge during

Electrolysis:

3NO , OH , 2

4SO , I , Cl ,

Br (1 mark)

1M H2SO4(aq)

A C


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(ii) Dilute magnesium sulphate solution was electrolysed using copper electrodes.

Write an ionic equation to show the reaction occurring at the: (2 marks)

Anode:

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Cathode:

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(e) An electric current of 2.5 amperes was passed through molten lead (II) bromide for 40

minutes. Calculate the volume of bromine vapour that would be produced (Faraday’s

constant = 96,500 coulombs, molar volume = 24.0dm³). (3 marks)

Chemistry Paper 2 7

5. (a) A student from a school in Nandi East carried out an experiment in order to find out the

effect of varying the molarity of sodium thiosulphate, on the time it took to react fully

with hydrochloric acid. She carried out the experiment at r.t.p. Using 50.0cm³ portions

of sodium thiosulphate in each case. Results obtained were tabulated as shown below.

Molarity of sodium thiosulphate in mol/1 1.2 1.0 0.8 0.6 0.4 0.2

Time (seconds) taken for the reaction to be completed 16 22 33 51 76 170

(i) State one observation likely to have been noted in the set up during this

experiment. (1 mark)

_____________________________________________________________________

_____________________________________________________________________

(ii) On the grid provided below draw a graph of the results (Molarity of thiosulphate

on y-axis against time taken -axis). (3 marks)


Chemistry Paper 2 8

(iii) State and explain the effect of varying the molarity of sodium thiosulphate on time taken to

complete reaction. (2 marks)

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(iv) I Using the graph to determine the molarity of sodium thiosulphate whose reaction

with the acid would take 42 seconds to be completed. (1 mark)


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II Determine the number of moles of hydrochloric acid required to react fully with

sodium thiosulphate of the above molarity in (iv), I.

aqOSNa 322 + aqHCl2 SS + gSO2 + aqNaCl2 + lOH 2 (2 marks)

(v) On the same grid above sketch a curve that is likely to be obtained. If the experiment

was repeated using the same reagents but whose temperature is at 35C. Label this

curve as “curve X”. (1 mark)

(b) Below is an equilibrium that is normally established in the Haber process.

gg HN 22 3 gNH 32 KJH 92 molˉ¹

Explain what would happen to the position of equilibrium if some water was introduced

into the equilibrium mixture. (1 mark)

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Chemistry Paper 2 9

6. The flow below represents the main steps in the preparation of sodium carbonate.

Solvay tower

Chamber X

Heat

Chamber Y

Ammoniated brine

NH4Cl

CO2(g)

CO2(g)

Heat

Slaker

Kiln

D

C

B

A

Brine


(a) Name the substance labeled. (2 marks)

A _________________________________________________________________________

B _________________________________________________________________________

C _________________________________________________________________________

D _________________________________________________________________________

(b) Cold water is made to circulate around chamber X. What does this suggest about the

reaction between A and brine. (½ mark)

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(c) What process takes place in chamber Y? (½ mark)

___________________________________________________________________________

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(d) Name two by-products that are recycled in this process. (1 mark)

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(e) Why is recycling important? (1 mark)

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(f) Write the equation for the reaction that takes place in the Solvay Tower.

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Chemistry Paper 2 10

(g) Assuming that there was no recycling in this process, two moles of ammonia would be

required for producing one mole of an hydrous sodium carbonate. Calculate the volume


of ammonia at s.t.p. that would be used to produce 10.6kg of sodium carbonate by a factory

operating at 80% efficiency. (C = 12, O = 16, H = 1, Na = 23, N = 14, 1 mole of gas

occupies 22.4dm³ at s.t.p). (3 marks)

(h) Give two industrial uses of sodium carbonate. (2 marks)

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___________________________________________________________________________

7. The extraction of aluminium from its ore takes place in two stages, purification stage and

electrolysis. The diagram below shows the set up for the electrolysis stage.

(a) Name the ore from which aluminium is extracted. (1 mark)

___________________________________________________________________________

(b) Name one impurity which is removed at purification stage. (1 mark)

___________________________________________________________________________

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Molten aluminium oxide


Chemistry Paper 2 11

(c) Write equation for the reactions that take place at:

(i) The anode. (1 mark)

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(ii) The cathode. (1 mark)

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(d) Explain why the anode has to be replaced from time to time. (1 mark)

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(e) The melting point of aluminium oxide is 2054C but electrolysis is done between 800C -

900C.

(i) Why is electrolysis not carried out at 2054C. (1 mark)

_____________________________________________________________________

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(ii) What is done to lower the temperature of the electrolysis cell to 800C - 900C.

(1 mark)

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(iii) The aluminium which is produced is tapped off as liquid. What does this imply about

its melting point? (1 mark)

_____________________________________________________________________

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(f) State one use of aluminium and the property related to this use. (2 marks)

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ANSWERS:

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