the nakuru district joint mock examination- … mocks/2012 nakuru district mock chemistry... ·...

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

SIGNATURE………………

233/3

CHEMISTRY

PRACTICAL

Paper 3

JULY 2012

TIME: 2¼ HOURS

THE NAKURU DISTRICT JOINT MOCK EXAMINATION- 2012 Kenya Certificate of Secondary Education

CHEMISTRY

Paper 3

PRACTICAL

2¼ HOURS

Instruction to Candidates

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

2. You are NOT allowed to start working with the apparatus for the first 15 minutes of the 2¼

hours allowed for this paper. This time is to enable you to read the question paper and make sure

you have all the chemicals and apparatus that you may need.

3. Mathematical tables and electronic calculators may be used

4. All working MUST be shown where necessary.

5. Candidates may be penalized for NOT following the instruction given in this paper.

For Examiners use only

Question Max. Score Score

1 12

2 12

3 a)

b)

5

11

Total score 40

This paper consist of 7 printed pages

Candidate should check the question paper to ensure that all the papers are printed

as indicated and no questions are missing.


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1 You are provided with: - Solution A containing 38.6 g per litre of solid A

(solid A is a mixture of sodium chloride and hydrated sodium carbonate) - Solution B which is 0.25M hydrochloric acid - Methyl orange indicator

You are required to determine the percentage of sodium chloride in the mixture.

Procedure

i) Fill your burette with solution B ii) Using a pipette and pipette filler, pipette 25cm3 of solution A into a conical

flask. Add two to three drops of methyl orange indicator.

iii) Titrate and record your results in the table below

Repeat the procedure to obtain consistent results.

I II III

Final burette reading (cm3)

Initial burette reading (cm3)

Volume of B used (cm3)

Find ( 4 marks)

a)(i) Average volume of B used (show values averaged)

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Calculate

ii) The number of moles of B. hydrochloric acid used. (H=1, CL=35.5) (1mark)

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iii) The number of moles of sodium carbonate, Na 2CO3.10H2O in 25.0cm3 of the mixture

(Na =23, C=12, O=16, H=1) (1mark)

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iv) Number of moles of sodium carbonate decahydrate in 1dm3 of the mixture of solution A

(2marks)

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b) Calculate the mass of sodioum carbonate Na 2CO3.10H2O, in the mixture made.

(Na =23, C=12, O=16, H=1) (2marks)

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c) Calculate the percentage by mass of sodium chloride in the mixture solution A (2 marks)

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2 You are provided with:

• Magnesium ribbon, solid L

• 2.0M hydrochloric acid, solution Q

• Stopwatch

You are required to determine the rate of reaction between magnesium and hydrochloric

acid at different concentrations.

Procedure

1 Place 5 test tubes on a test tube rack and label them 1,2,3,4,and 5.ing a 10ml measuring

cylinder measure out the volumes of 2M hydrochloric acid solution Q as shown in the table

and pour them into the corresponding test-tubes. Wash the measuring cylinder and use it to

measure the volumes of water as indicated in the table and pour into the corresponding test-

tubes.

II Transfer all of the solution in test tube I into a clean 50ml beaker. Place one piece of

magnesium ribbon into the beaker and start a stopwatch immediately. Swirl the beaker

continuously ensuring the magnesium is always inside the solution. Note the time taken for

the magnesium ribbon to disappear and record in the table. Wash the beaker each time.

III Repeat the procedure II for each case of the solution in the test tubes 2,3,4 and 5 to

complete the table.

Table 1

Test tube number 1 2 3 4 5

Volume of solution Q(cm3) 10 9 8 7

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Volume of distilled water(cm3) 0 1 2 3 4

Time taken (sec)

Rate of reaction 1

time

(6marks)

(b) Plot a graph of rate of reaction, 1 (y-axis) against volume of solution A (4marks)

time


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ii) Use the graph to determine the time that would be taken for a 1cm length of magnesium ribbon

to disappear if the volume of the acid solution Q used was 7.5cm3

(1mark)

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(iii) In terms of rate of reaction, explain the shape of your graph (1 marks)

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3 You are provided with

Solution W containing calcium ions

Solution X containing sodium ions

Solution Y containing barium ions

Carry out the tests on solutions W,X,Y and Z in order to identify the cations present in solution

Z

Procedure


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Clean one end of the glass rod thoroughly dip the clean end of the glass rod in solution W..

Remove the end and heat it in the non – luminous

part of a Bunsen burner flame. Note the colour of the flame and record it in table 3. Allow the

glass rod to cool for about two minutes. Repeat the procedure with solutions X,Y and Z.

Complete table 3

Table 3

solution Colour of the flame

W

X

Y

Z

(4marks)

(ii) Identify the cation present in solution Z (1mark)

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b) You are provided with solid K. Carry out the tests below and record your observations and

inferences in the spaces provided.

(a) Place one half of solid K in a clean dry test-tube. Heat it gently then strongly.

Observation Inferences


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(2marks) (1mark)

b) Place the other half of solid K in a boiling tube. Add 10cm3 of distilled water and shake well until

all the solid dissolves

(i) To about 1cm3 of the solution add 2M sodium hydroxide drop wise until in excess

Observation inferences

(2marks) (1mark)

ii) Place 1cm3

of the solution in a test tube and add 2 to 3 drops of 2M sulphuric (vi) acid.



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(1mark) (1mark)

iii) To about 1cm3 of the solution, add 4 to 5 drops of 2M lead(II) Nitrate solution and heat to boiling.


(2 Marks) (1mark)

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