Chemistry Paper 3 Questions, Answers and Confidential - KCSE 2022 Mock Exams Set 1

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Instruction to the candidates

  1. Write your Name and Index Number, Admission Number and Class in the spaces provided at the top of this
  2. Answer all the questions in the spaces in the spaces provided in this paper using English.
  3. KNEC Mathematical tables and silent electronic calculators may be
  4. All working MUST be clearly shown where

For Examiner’s use only

Questions

Maximum score

Candidate’s Score

1

11

 

2

09

 

3

20

 

 

40

 

QUESTIONS

  1. You are provided with:
  • Solution A, potassium iodate solution.
  • Solution B, acidified sodium hydrogen sulphite solution.
  • Solution C, starch indicator.
  • Stop watch.
  • Distilled water.

You are required to find out the effect of concentration of potassium iodate, A on the rate of reaction with acidified sodium hydrogen sulphite, B.
NB: The end point of reaction of potassium iodate with acidified sodium hydrogen sulphite is indicated by the formation of a blue colored complex using starch indicator.
Procedure 1:
Step 1

  • Label 5 test tubes as 1, 2, 3, 4 and 5 and place them in a test tube rack.

Step 2

  • Using a 10 cm3 measuring cylinder add 5 cm3 of acidified sodium hydrogen sulphite, solution B to each of the test tube in the rack.

Step 3

  • Using a burette pour 10 cm3 of potassium iodate solution to the first test tube.

Step 4

  • Add 8 cm3 of potassium iodate solution to the second test tube, 6 cm3 to the third test tube, 4 cm3 to the fourth test tube and 2 cm3 to the fifth test tube.

Step 5

  • Using a 10 cm3 measuring cylinder add 2 cm3 of distilled water into the second test tube, 4 cm3 to the third test tube, 6 cm3 to the fourth test tube and 8 cm3 to the fifth test tube.

Step 6

  • Using a 10 cm3 measuring cylinder add 10 cm3 of solution B into a 100 cm3 beaker, add 3 drops of solution C and shake well. To this mixture add quickly contents in the first test tube and start a stopwatch immediately. Shake the mixture and note the time taken for the blue color to appear. Record the time taken in table I.

Step 7

  • Rinse the beaker and repeat procedure in step 6 using the other solutions prepared in step 4 above and complete the table I.

Table I                                                                                                                    

Experiment

Volume of Sodium hydrogen sulphite (NaHSO3) used (cm3)

Volume of distilled water used (cm3)

Volume of potassium iodate (KIO3) used in (cm3)

Time taken to change color (secs)

1

5

0

10

 

2

5

2

8

 

3

5

4

6

 

4

5

6

4

 

5

5

8

2

 

(3 marks)

  • On the grid below plot a graph of time taken for the color change against volume of aqueous potassium iodate used. (3 marks)

graph paper sdsf

  1. From your graph determine the time taken for the blue colour to appear if 7cm3 of aqueous potassium iodate was used.(1 mark)
  2. Calculate the volume of distilled water required if 7 cm3 of aqueous potassium iodate was used.(1 mark)

c). On the graph sketch the graph that could be expected if the above experiments were done at a higher temperature. Explain. (1 mark)
d). How does the volume of potassium iodate solution A, affect its rate of reaction with acidified sodium hydrogen sulphite B? Explain your answer. (2 marks)

  1. You are provided with:
    • Solution D, which is 0.05M acidified potassium manganate (VII) solution (KMnO4).
    • Solution E, containing 5.0g/l of a dibasic acid, H22H2O

You are required to determine the concentration of dibasic acid H2M.2H2O, solution E and then the formula mass of M.
Procedure II

  1. Fill the burette with solution D.
  2. Using a clean pipette, place 25 cm3 of solution E into a clean conical flask. Heat this solution to about 700
  3. Titrate using solution D until a permanent pink colour just appears. Shake thoroughly during titration.
  4. Record the reading in table II
  5. Repeat the titration one more time to complete the table below.

a). Complete the table II
Table II

Titration

I

II

III

Final burette reading (cm3)

     

Initial burette reading (cm3)

     

Volume of solution D used (cm3)

     

 (3 marks)

b). Determine the average volume of solution D (1 mark)
c). Calculate:

  1. The number of moles of manganate (VII) ions in the average volume of solution B used above. (1 mark)
  2. Given that 2 moles of manganate (VII) ions react with 5 moles of dibasic acid H2M.2H2O. Calculate the number of moles of the dibasic acid H2M.2H2O in the 25 cm3 of solution E.(1 mark)
  3. The concentration of solution E in moles per litre. (1 mark)
  4. Calculate the formula mass of M in the dibasic acid H2M.2H2O.  (H = 1, O=16). (2 marks)
  1. (a) You are provided with solid F. Carry out the tests below. Write your observations and inferences in the spaces

i). Place about one third of solid F in a clean dry test-tube and heat it strongly.

Observations

Inference

   
(1 mark) (1 mark)

ii). Place the remaining solid F in a boiling tube. Add about 10 cm3 of distilled water. Shake the mixture thoroughly for about one minute.
Filter and divide the filtrate into four portions.

Observations

Inference

   
 (1 mark)  (1 mark)

I. To the first portion, add 2 drops of phenolphthalein indicator.

Observations

Inference

   
 (1 mark)  (1 mark)

II). To the second portion, add 2 cm3 of dilute sulphuric (VI) acid.

Observations

Inference

   
   
 (1 mark)  (1 mark)

III). To the third portion, add 3 cm3 of aqueous potassium iodide.

Observations

Inference

   
 (1 mark)  (1 mark)

IV). To the fourth portion, add dilute ammonia solution drop wise  until excess

Observations

Inference

   
 (1 mark)  (1 mark)

b). You are provided with solid G. Carry out the following tests and record your observations and inferences in the spaces provided.
i). Using a metallic spatula, take one third of solid G and ignite it using a Bunsen burner flame.

Observations

Inference

   
 (1 mark)  (1 mark)

ii). Place the remaining solid G in a boiling tube. Add about 10cmdistilled water. Shake the mixture well. Divide the mixture into two portions.

Observations

Inference

   
 (1 mark)  (1 mark)

I. To about 4cm3 of the solution, add solid sodium carbonate and shake well.

Observations

Inference

   
 (1 mark)  (1 mark)

II. To about 4 cm3 of the solution, add 3 drops of acidified potassium dichromate (VI). Warm the mixture.

Observations

Inference

   
 (1 mark)  (1 mark)

MARKING SCHEME

QUESTION 1
Table

  1. Complete table
  2. Decimal place
  3. Principals of averaging
  4. Accuracy         –    Compare candidates values to school values (s.v)
    • At least one value within ± 0.1 of s.v
    • If within ± 0.2 of s.v

 

  1.                      
    1. Average volume of solution A     
      Final accuracy
    2. 1 x 60  = 0.24M or 0.24 moles/litre
        250
    3. RFM of HCl = 1 + 35.5 = 36.5
      Concentration of HCl in g/litre
      = ans in a(ii) x 36.5 = ans
                  1 litre
    4. ans in a(i) x ans in a(ii) = ans
                1000
  2.                          
    1. Mole Ratio = 1 : 1
      no of moles of soln Q = ans in a (iv)
    2. ans in b(i) x 1000 = ans
                25       
    3. ans in b(ii) x 750 = ans     or        ans in b (i) x 750 = ans
                1000                                             25
    4.     1 x 4.2     = ans
      ans in b(iii)
    5. 16 + 1 = 17
      R.A.M of x = ans in b(iv) – 17

2[i]

Observation

inference

Solid dissolves to form colourless solution

Coloured ions  absent or

Cu2+,Fe2+,Fe2+absent

[ii]

Observation

Inference

White ppt which dissolves on excess to form colourless solution

Zn 2+,Pb2+,Al3+present

[iii]

observation

inference

White ppt formed which dissolves in Excess to form colourless solution

Zn2+ present

[iv]

observation

Inference

No white ppt formed

CO2-3 , SO24 ,absent

[v]

   

White ppt formed which dissolves on warming

To form  colourless solution

Cl-present

3.[a]

Observation

Inference

Burns in yellow sooty smoky flame

Unsaturated organic compound

   C=C ,  -C≡C- present

[b]

observation

inferences

Does not dissolve it forms Layers

Non polar organic Compound

observation

inferences

Purple Potassium Manganate (VII) colourless

 C=C  , -C≡C-, R-OH present

CONFIDENTIAL

Instructions to Schools:
The information contained in this paper is to enable the head of the school and the teacher in charge of Chemistry to make adequate preparation for the Chemistry Practical Examination.
NO ONE ELSE should have access to this paper or acquire knowledge of its content. Great care MUST be taken to ensure that the information herein does NOT reach the candidates either directly or indirectly. The teacher in charge of Chemistry should NOT perform any of the experiments in the SAME room as the candidates nor make the results of the experiment available to the candidates of give any information related to the experiments to the candidates. Doing so will constitute an examination irregularity.

REQUIREMENTS FOR CANDIDATES
In addition to fittings, and apparatus found in the chemistry laboratory, each candidate will require:

  1. 100 cm3 of Solution A – Potassium iodate solution, KIO3.
  2. 50 cm3 of Solution B – Acidified sodium hydrogen sulphite, NaHSO3.
  3. About 30 cm3 of Solution C – Starch indicator solution.
  4. 150 cm3 of Solution D – Acidified potassium manganite (VII), KMnO4.
  5. 150 cm3 of Solution E – 5g/l of dibasic acid, H22H2O.
  6. About 1g of Solid F – Calcium hydroxide in a stoppered boiling tube.
  7. About 1g of Solid G – Pure maleic acid .in a stopper container.
  8. About 0.5g of sodium carbonate.
  9. Distilled water.
  10. One 50 cm3
  11. One 25 cm3
  12. One 10 cm3 measuring cylinder.
  13. One 100 cm3
  14. Six, clear dry test-tubes placed in a rack.
  15. One stop watch / stop clock.
  16. One boiling tube.
  17. One spatula metallic.

ACCESS TO:

  1. Phenolphthalein indicator supplied with a dropper.
  2. 2M Sulphuric (VI) acid supplied with a dropper.
  3. Aqueous potassium iodide supplied with a dropper – KI.
  4. 2M Ammonia solution supplied with a dropper
  5. Source of heat (Bunsen burner).
  6. Acidified potassium dichromate (VI) – K­2­Cr2O7.

PREPARATIONS

  1. Solution A is prepared by dissolving 2g of solid A (Potassium iodate) in distilled water and making it up to one litre.
  2. Solution B is prepared by dissolving 0.40 g of solid B (Sodium hydrogen sulphite) in about 200 cm3 of distilled water, and adding 20 cm3 of 1M sulphuric acid, shaking well, and making up to one litre with distilled water.
  3. Solution C is prepared placing 1.0g of solid C (Starch) in 100 cm3 beaker and adding 2 cm3 of distilled water to make a paste and pouring the paste into 100 cm3 of boiling distilled water and boiling the mixture for about one minute and allowing it to cool solution C is to be prepared in the morning of the examination.
  4. Solution D is prepared by dissolving 9g of solid potassium manganate(VII) in about 600 cm3 of 2M sulphuric(VI) acid and adding distilled water to make a litre of the solution.
  5. Solid G is pure maleic acid.
  6. Solution E prepared by dissolving 5 g of oxalic acid in 250 cm3 of water and making it to one litre of solution.

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