Chemistry Paper 3 Questions and Answers - Kassu Jet Pre Mocks 2022

INSTRUCTIONS TO CANDIDATES:

• Answer all the questions in the spaces provided in the question paper.
• You are NOT allowed to start working within the first 15 minutes of the 2 ¼ hours allowed for this paper. This time is to enable you read the question paper and make sure you have all the chemicals and apparatus that you may need.
• All working MUST be clearly shown.
• Mathematical tables and silent scientific calculators may be used.
• Candidates should check to ascertain that all papers are printed as indicated and that no questions are Missing

For Examiner’s Use Only:

Question	Maximum score	Candidate’s score	Examiner’s initials
1	14
2	10
3	10
4	06
Total  score	40

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QUESTIONS

1. You are provided with:
   • Solution A₁, potassium iodate solution
   • Solution A₂, acidified sodium hydrogen sulphite solution
   • Solution A₃ starch indicator
   • Distilled water in a wash bottle.
   • Stop watch / stop clock

You are required to find out the effect of concentration of potassium iodate A₁ on the rate of reaction with acidified sodium hydrogen sulphite A₂.
Note: the end point of reaction of potassium iodate with acidified sodium hydrogen sulphite is indicated in the formation of a blue coloured complex using starch indicator.
Procedure 1:

• Using a 10 cm³ measuring cylinder to pour 5 cm³ of aqueous sodium hydrogen sulphite into the conical flask.
• Use another 10 cm³ of measuring cylinder to pour 5 cm³ of starch solution into the same conical flask.
• Using a burette pour 15 cm³ of distilled water into the same beaker.
• Using a burette pour 20 cm³ of aqueous potassium iodate into the beaker and immediately start the stop watch.
• Swirl the mixture in the conical / flask and continue to swirl until a sudden blue colour change is seen.
• Stop the stop-watch and record time taken seconds for the sudden blue colour change to appear.
• Rinse the beaker with water.

Experiment 2:

• Repeat procedure 1 using 17 cm³ of distilled water and 18 cm³ of aqueous potassium iodate.
• Repeat procedure 1 using 21 cm³ of distilled water and 14cm³ of aqueous potassium iodate.
• Repeat experiment 1 using 23 cm³ of distilled water and 12 cm³ of aqueous potassium iodate.
• Repeat experiment 1 using 25 cm³ of distilled water and 10 cm³ of aqueous potassium iodate.

(a) Complete the table below. 
Table I

Experiment	1	2	3	4	5
Volume of Sodium hydrogen sulphite (Na HSO3) used	5	5	5	5	5
Volume of distilled water used (cm3)	15	17	21	23	25
Volume of potassium iodate (KIO3 (aq) used in cm3	20	18	14	12	10
Time taken to change colour (secs)

(4 marks)

(b) On the grid below plot a graph of time taken (secs) for the colour change (vertical axis) against volume of aqueous potassium iodate used (cm³). (3 marks)

(c)

1. From your graph determine the time taken for the blue colour to appear if 16 cm³ of aqueous potassium iodate was used. (Show clearly on the graph how you worked out your answer).  (1 mark)
2. Calculate the volume of distilled water required if 16 cm³ of aqueous potassium iodate was used.  (1 mark)

(d) On the graph sketch the graph that could be expected if the above experiment s were done at a higher temperature. Explain. (1 mark)
(e) Calculate the concentration of potassium iodate solution in moles per litre in the final reaction mixture in the experiment 1. (2 marks)
(f) How does the concentration of potassium iodate solution A₁, affect its rate of reaction with acidified sodium hydrogen sulphite A₂? Explain your answer.    (2 marks) 

2. You are provided with:

• Solution B, which is 0.05M acidified potassium manganate (VII) solution (KMnO₄).
• Solution C, containing 5.0g/l of a dibasic acid, H₂ 2H₂O

You are required to:

• Determine the concentration of dibasic acid H₂X, solution C and then the formula mass of X.

Procedure II

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

Complete the table I below.
Table I

	I	II
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of solution b used cm

(3 marks)

1.                    
2. Determine the average volume of solution B used. (1 mark)
   1. Calculate:
   2. The number of moles of manganate (VII) ions in the average volume of solution B used above. (1 mark)
   3. Given that 2 moles of manganate (VII) ions react with 5 moles of dibasic acid H₂ X.2H₂O. Calculate the number of moles of the dibasic acid H₂ X.2H₂O in the 25 cm⁵ of solution C. (2 marks)
   4. The concentration of solution C in moles per litre. (1 mark)
   5. Calculate the formula mass of X in the dibasic acid H₂ 2H₂O (H = 1, O = 16) (2 marks)

3. You are provided with solution Q. Carry out the tests below. Write your observations and inferences in the spaces provided.Place about 2 cm³ of the solution in five separate test-tubes.

a). To the first portion, add aqueous sodium hydroxide drop wise until in excess.

Observations	Inferences
(1 mark)	(1 mark)

b). To the second portion, add aqueous ammonia dropwise until in excess.

Observations	Inferences
(1 mark)	(1 mark)

c). To the third portion, add 3 drops of dilute hydrochloric acid.

Observations	Inferences
(1 mark)	(1 mark)

d). To the fourth portion, add 3 drops of barium nitrate solution.

Observations	Inferences
(1 mark)	(1 mark)

e). To the last portion, add 3 drops of lead (II) nitrate solution then warm the mixture.

Observations	Inferences
(1 mark)	(1 mark)

4. You are provided with solid R. Carry out the tests below. Write your observations and inferences in the spaces provided.
i). Place one third of solid R on a metallic spatula. Burn it in non-luminous flame of the Bunsen burner.           

Observations	Inference
( ½ mark)	( ½ mark)

ii). Place the remaining solid in a test-tube. Add about 6 cm³ of distilled water and shake the mixture well. Retain the solution for the next procedure.

Observations	Inferences
( ½ mark)	( ½ mark)

I). In another 2 cm³,  add 2 drops of acidified potassium manganate (VII). 

Observations	Inferences
(1 mark)	(1 mark)

(II) To about 1cm³, add 3 drops of acidified potassium dichromate (VI) and warm.

Observations	Inferences
( ½  mark)	( ½  mark)

(III)  To about 2 cm³ of the solution, add 1g of solid D; sodium hydrogen carbonate.

Observations	Inferences
( ½  mark)	( ½  mark)

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MARKING SCHEME

1. You are provided with:
   • Solution A₁, potassium iodate solution
   • Solution A₂, acidified sodium hydrogen sulphite solution
   • Solution A₃ starch indicator
   • Distilled water in a wash bottle.
   • Stop watch / stop clock

You are required to find out the effect of concentration of potassium iodate A₁ on the rate of reaction with acidified sodium hydrogen sulphite A₂.
Note: the end point of reaction of potassium iodate with acidified sodium hydrogen sulphite is indicated in the formation of a blue coloured complex using starch indicator.
Procedure 1:

• Using a 10 cm³ measuring cylinder to pour 5 cm³ of aqueous sodium hydrogen sulphite into the conical flask.
• Use another 10 cm³ of measuring cylinder to pour 5 cm³ of starch solution into the same conical flask.
• Using a burette pour 15 cm³ of distilled water into the same beaker.
• Using a burette pour 20 cm³ of aqueous potassium iodate into the beaker and immediately start the stop watch.
• Swirl the mixture in the conical / flask and continue to swirl until a sudden blue colour change is seen.
• Stop the stop-watch and record time taken seconds for the sudden blue colour change to appear.
• Rinse the beaker with water.

Experiment 2:

• Repeat procedure 1 using 17 cm³ of distilled water and 18 cm³ of aqueous potassium iodate.
• Repeat procedure 1 using 21 cm³ of distilled water and 14cm³ of aqueous potassium iodate.
• Repeat experiment 1 using 23 cm³ of distilled water and 12 cm³ of aqueous potassium iodate.
• Repeat experiment 1 using 25 cm³ of distilled water and 10 cm³ of aqueous potassium iodate.

(a) Complete the table below. 
Table I

Experiment	1	2	3	4	5
Volume of Sodium hydrogen sulphite (Na HSO3) used	5	5	5	5	5
Volume of distilled water used (cm3)	15	17	21	23	25
Volume of potassium iodate (KIO3 (aq) used in cm3	20	18	14	12	10
Time taken to change colour (secs)	196	205	240	338	440

(4 marks)

(b) On the grid below plot a graph of time taken (secs) for the colour change (vertical axis) against volume of aqueous potassium iodate used (cm³). (3 marks)

(c)

1. From your graph determine the time taken for the blue colour to appear if 16 cm³ of aqueous potassium iodate was used. (Show clearly on the graph how you worked out your answer).  (1 mark)
   18.5 x 10¹ = 185 seconds 
   time correct to their working
2. Calculate the volume of distilled water required if 16 cm³ of aqueous potassium iodate was used.  (1 mark)
   35 - 16 = 19cm³
   increase in temperature leads to increase in rate of reaction or less time taken to react

(d) On the graph sketch the graph that could be expected if the above experiment s were done at a higher temperature. Explain. (1 mark)
line is below plotted line 
(e) Calculate the concentration of potassium iodate solution in moles per litre in the final reaction mixture in the experiment 1. (2 marks)
0.05    →   8 KIO³ - 1000cm³
x     →   20cm³
x = 0.05 x 20
        1000
= 0.001 moles
0.001 moles KIO³    →   45cm³
x    →   1000
x = 0.001 x 1000 = 0.02222M
            45
(f) How does the concentration of potassium iodate solution A₁, affect its rate of reaction with acidified sodium hydrogen sulphite A₂? Explain your answer.    (2 marks) 
increase in concentration leads to increase in the rate of reaction hence less time to react. The more the concentration (moles) number of particles leads to more collisions hence less time taken to react

2. You are provided with:

• Solution B, which is 0.05M acidified potassium manganate (VII) solution (KMnO₄).
• Solution C, containing 5.0g/l of a dibasic acid, H₂ 2H₂O

You are required to:

• Determine the concentration of dibasic acid H₂X, solution C and then the formula mass of X.

Procedure II

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

Complete the table I below.
Table I

	I	II
Final burette reading (cm3)	8.0	8.0
Initial burette reading (cm3)	0.0	0.0
Volume of solution b used cm	8.0	8.0

(3 marks)

1.              
2. Determine the average volume of solution B used. (1 mark)
   8.0 + 8.0 = 16.0 = 8.0cm3 ± 0.2
       2              2
3. Calculate:
   1. The number of moles of manganate (VII) ions in the average volume of solution B used above. (1 mark)
      0.05 moles → 1000 cm
      x →  8 cm
      x = 0.05 x 8 = 0.004 moles
               1000
   2. Given that 2 moles of manganate (VII) ions react with 5 moles of dibasic acid H₂ X.2H₂O. Calculate the number of moles of the dibasic acid H₂ X.2H₂O in the 25 cm⁵ of solution C. (2 marks)
      MnO₄:H⁺
      2:5
      0.0004:x
      x = 0.0004 x 5
                  2
      = 0.001 moles
   3. The concentration of solution C in moles per litre. (1 mark)
      0.001 moles of C → 25 cm³
      x  → 1000 cm
      x = 0.001 x 1000
                      25
      = 0.04m
   4. Calculate the formula mass of X in the dibasic acid H₂ 2H₂O (H = 1, O = 16) (2 marks)
      molarity  =  g/l  
                      R.Fm
      0.04 = 5g/l
                  x
      x = 5 ÷ 0.04 = 125
      H₂A.2H₂O = 125
      2 + x +2 (18) = 125
      x = 125 - 36 - 2
      =87

3. You are provided with solution Q. Carry out the tests below. Write your observations and inferences in the spaces provided.Place about 2 cm³ of the solution in five separate test-tubes.

a). To the first portion, add aqueous sodium hydroxide drop wise until in excess.

Observations	Inferences
white precipitate soluble in excess	Zn2+, Al3+, Pb2+ present

b). To the second portion, add aqueous ammonia dropwise until in excess.

Observations	Inferences
White precipitataae insoluble in excess	Al3+, Pb2+ present

c). To the third portion, add 3 drops of dilute hydrochloric acid.

Observations	Inferences
No white precipitate  No effervescence	Al3+ present, Pb2+ absent SO32-, CO32-, HCO3- absent

d). To the fourth portion, add 3 drops of barium nitrate solution.

Observations	Inferences
No white precipitate	SO42- absent

e). To the last portion, add 3 drops of lead (II) nitrate solution then warm the mixture.

Observations	Inferences
White precipitate that dissolves in warming	Cl- present

4. You are provided with solid R. Carry out the tests below. Write your observations and inferences in the spaces provided.
i). Place one third of solid R on a metallic spatula. Burn it in non-luminous flame of the Bunsen burner.           

Observations	Inference
Burns with a yellow sooty flame

ii). Place the remaining solid in a test-tube. Add about 6 cm³ of distilled water and shake the mixture well. Retain the solution for the next procedure.

Observations	Inferences
dissolves to form a colourless solution homogeneous mixture	polar compund

I). In another 2 cm³,  add 2 drops of acidified potassium manganate (VII). 

Observations	Inferences
acidified potassium manganate (vii) changes colour from purple to colourless	R-OH present

(II) To about 1cm³, add 3 drops of acidified potassium dichromate (VI) and warm.

Observations	Inferences
Yellow acidified potassium dichromate (vi) remains yellow	R-OH absent

(III)  To about 2 cm³ of the solution, add 1g of solid D; sodium hydrogen carbonate.

Observations	Inferences
Effervesce and bubbles of a colourless gas given out	O                           II H+, H3O+, R-C-O-H present

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CONFIDENTIAL

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 A₁ – KIO₃, potassium iodate solution
2. 100 cm³ of solution A₂ – Acidified NaHSO₃, Acidified sodium hydrogen sulphite
3. 150 cm³ of solution B acidified potassium manganite (VII) KmnO₄
4. 150 cm³ of solution C, 5g/l of dibasic acid, H₂2H₂O
5. About 1g of solid R in a stopper container – maleic acid (pure)
6. About 1g of solid D (sodium hydrogen carbonate)
7. One 50 cm³ burette
8. About 30 cm³ of A₃, starch indicator solution.
9. About 10 cm³ solution Q (Al Cl_{3 (aq)}) in a stoppered boiling tube
10. One 25 cm³ pipette
11. Two 10 cm³ measuring cylinder
12. One 100 cm³ beaker
13. Two 250 cm³ conical flasks
14. Seven, 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. 2M sodium hydroxide solution supplied with a dropper.
2. 2M Ammonia solution supplied with a dropper
3. 2M dilute hydrochloric acid supplied with a dropper.
4. 2M Barium nitrate solution supplied with a dropper.
5. 2M Lead (II) nitrate solution supplied with a dropper.
6. 300 cm² of distilled water.
7. Source of heat (Bunsen burner).
8. Acidified potassium manganite (VII) – KmnO₄ supplied with a dropper.
9. Acidified potassium dichromate(VI) – K­2­Cr₂O₇.­

PREPARATIONS

1. Solution A₁ is prepared by dissolving 2g of solid A₁ (potassium iodate [KIO_3(s)]) in distilled water and making it up to one litre.
2. Solution A₂ is prepared by dissolving 0.40 g of solid A₂ acidified sodium hydrogen sulphite (NaHSO₃) 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 A₃ – starch indicator is prepared placing 1.0g of solid A₃ – starch indicator 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 A₃ is to be prepared in the morning of the examination.
4. Solution B – Acidified potassium manganate(VII) 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 R is pure maleic acid.
6. Solution C – 5g/l of oxalic acid is 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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