Chemistry Paper 3 Pre Mock Questions, Answers and Confidential - Mokasa I Joint Examination July 2021

INSTRUCTIONS TO CANDIDATES

• Write your name and index number in the spaces provided.
• Sign and write the date of examination in the spaces provided.
• Answer all the questions in the spaces provided in the question paper
• 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 required.
• All working must be clearly shown where necessary
• Mathematical tables and electronic calculators may be used.
• This paper has 7 printed pages. Check to confirm that it is so.

FOR EXAMINER’S USE ONLY

QUESTIONS

1.                                    
   1. You are provided with:
      • Solution A ,containing 39.2g/l of FeSO₄(NH₄)₂SO₄.nH₂O
      • Solution B Containing 3.0g/l of KMnO₄.
        You are required to determine;
      • The concentration of solution A in moles per litre
      • The number of moles of (n) of water of crystallization in FeSO₄(NH₄)₂SO₄.nH₂O

Procedure

• Fill the burette with solution A.
• Using a pipette filler, pipette 25.0cm³ of solution B into a conical flask and titrate with solution A until a pink colour just appears.
• Record thevolume of solution A used in the table below. Repeat the experiment twice and fill the table.

Table 1

(4mks)

1. Calculate the average volume of solution A used (1mk)
2. Determine;
   1. Concentration of solution B in moles per litre, (1mk)
      (K=39,Mn=55,O=16)
   2. Number of moles of solution B used. (1mk)
3. Given that the ionic equation for the reaction is:
   MnO₄^-_(aq)+8H⁺_(aq)+5Fe²⁺_(aq)    →     Mn²⁺_(aq)+5Fe³⁺_(aq)+4H₂O _(l)
   Determine the number of moles of solution A used. (1mk)
   Determine the;
   1. Concentration of solution A in mole per litre (1mk)
   2. Relative formula mass of FeSO₄(NH₄)₂SO₄.nH₂O (1mk)
   3. Number of moles of water of crystallization (n) in FeSO₄(NH₄)₂SO₄.nH₂O (1mk)

b. You are provided with 2.0g of solid R in a boiling tube.
You are required to determine the solubility of solid R at different temperatures.
Procedure

1. Using a burette, add 3.0cm3 of distilled water into the boiling tube with solid R.
2. Gently heat the boiling tube, while stirring the contents carefully with a thermometer until the crystals of R dissolve completely.
3. Remove the boiling tube from the flame and allow the contents to cool while stirring with the thermometer. Note the temperature at which crystals just appear and record it in Table II below.
4. Add 2.0cm³ of distilled water from the burette into the boiling tube containing the mixture and repeat steps (ii) and (iii) above.
5. Repeat step (iv) three more times.
6. Calculate the solubility of solid R in water at the different temperatures and complete table 2.

Table 2

(5½ marks)

1. On the grid provided, plot a graph of solubility of solid R (vertical axis) against temperature(horizontal axis ) (3 marks)
   
2. From your graph, determine
   1. The temperature at which 35g of solid R would dissolve in 100cm³ of water.(1mk)
   2. The solubility of solid R at 50oC. (1mk)
   3. State how solubility varies with temperature. (½mk)

2. You are provided with solid Q. Carry out the tests below and record your observations and inferences in the spaces provided.

1. Place all of solid Q in a clean boiling tube. Add about 10cm³ of distilled water and shake. Divide the resulting solution into 4 equal portions.
   

   Observations	Inference
   (1mk)	(1mk)

   
   
   1. To the 1st portion, add drops of sodium sulphate solution.
      
      

      Observations	Inference
      (1mk)	(1mk)

   2. To the 2nd portion, add sodium hydroxide solution dropwise until excess.
      
      

      Observations	Inference
      (1mk)	(1mk)

   3. To a 3rd portion, add ammonia solution dropwise until in excess.
      
      

      Observations	Inference
      (1mk)	(1mk)

   4. To the fourth portion, add 2-3 drops of acidified barium nitrate solution.
      
      

      Observations	Inference
      (1mk)	(1mk)

3. You are provided with solid F. Carry out the tests and record your observations and inferences in the spaces provided.

1. Place half a spatulaful of solid F in a non-luminous flame to ignite.
   
   

   Observations	Inference
   (1mk)	(1mk)

2. Place the rest of the solid in a test-tube. Add about 6cm³ of distilled water and shake the mixture well. Divide the solution into 3 portions.
   
   

   Observations	Inference
   (1mk)	(1mk)

3. To about 2cm3 of the solution, add a spatulaful of sodium hydrogen carbonate.
   
   

   Observations	Inference
   (1mk)	(1mk)

4. To about 2cm³, add 2 drops of acidified potassium manganate (vii) solution.
   
   

   Observations	Inference
   (1mk)	(1mk)

5. To another 2cm³, add 2 drops of bromine water.
   
   

   Observations	Inference
   (1mk)	(1mk)

MARKING SCHEME

1.                                    
   1. You are provided with:
      • Solution A ,containing 39.2g/l of FeSO₄(NH₄)₂SO₄.nH₂O
      • Solution B Containing 3.0g/l of KMnO₄.
        You are required to determine;
      • The concentration of solution A in moles per litre
      • The number of moles of (n) of water of crystallization in FeSO₄(NH₄)₂SO₄.nH₂O

Procedure

• Fill the burette with solution A.
• Using a pipette filler, pipette 25.0cm³ of solution B into a conical flask and titrate with solution A until a pink colour just appears.
• Record thevolume of solution A used in the table below. Repeat the experiment twice and fill the table.

Table 1

CT - 1
DP - 1
AC - 1
PA - 1
FA - 1
     05
(4mks)

1. Calculate the average volume of solution A used (1mk)
2. Determine;
   1. Concentration of solution B in moles per litre, (1mk)
      (K=39,Mn=55,O=16)
       3.0
      168
      =0.01786M
   2. Number of moles of solution B used. (1mk)
        25   × Ans (b)(i)
      1000
      
3. Given that the ionic equation for the reaction is:
   MnO₄^-_(aq)+8H⁺_(aq)+5Fe²⁺_(aq)    →     Mn²⁺_(aq)+5Fe³⁺_(aq)+4H₂O _(l)
   Determine the number of moles of solution A used. (1mk)
   Ans b(ii) × 5
   Determine the;
   1. Concentration of solution A in mole per litre (1mk)
      1000 × Ans (c)
      ans(a)
      Ans (c₂)
   2. Relative formula mass of FeSO₄(NH₄)₂SO₄.nH₂O (1mk)
      R.F.M = 39.2
                  Ans.c (i)
   3. Number of moles of water of crystallization (n) in FeSO₄(NH₄)₂SO₄.nH₂O (1mk)
      294 + 18n = ans(c₂)

b. You are provided with 2.0g of solid R in a boiling tube.
You are required to determine the solubility of solid R at different temperatures.
Procedure

1. Using a burette, add 3.0cm3 of distilled water into the boiling tube with solid R.
2. Gently heat the boiling tube, while stirring the contents carefully with a thermometer until the crystals of R dissolve completely.
3. Remove the boiling tube from the flame and allow the contents to cool while stirring with the thermometer. Note the temperature at which crystals just appear and record it in Table II below.
4. Add 2.0cm³ of distilled water from the burette into the boiling tube containing the mixture and repeat steps (ii) and (iii) above.
5. Repeat step (iv) three more times.
6. Calculate the solubility of solid R in water at the different temperatures and complete table 2.

Table 2

CT - 1
DP - ½
T  - ½
AC- 1
     03(5½ marks)

1. On the grid provided, plot a graph of solubility of solid R (vertical axis) against temperature(horizontal axis ) (3 marks)
   
   P - 1
   A - ½
   S - ½
   C - 1
       03
2. From your graph, determine
   1. The temperature at which 35g of solid R would dissolve in 100cm³ of water.(1mk)
      Shown from graph ½
      Value ½
   2. The solubility of solid R at 50ºC. (1mk)
      From graph 
   3. State how solubility varies with temperature. (½mk)
      Solubility increaes with increase in temperature

2. You are provided with solid F. Carry out the tests below and record your observations and inferences in the spaces provided.

1. Place all of solid F in a clean boiling tube. Add about 10cm³ of distilled water and shake. Divide the resulting solution into 4 equal portions.
   
   

   Observations	Inference
   Dissolves to form  a colourless solution	-soluble salt -Cu2+, Fe2+, Fe3+ absent

i)To the 1st portion, add drops of sodium sulphate solution

ii)To the 2nd portion, add sodium hydroxide solution dropwise until excess

iii)To a 3rd portion, add ammonia solution dropwise until in excess.

iv)To the fourth portion, add 2-3 drops of acidified barium nitrate solution.

3. You are provided with solid Q. Carry out the tests and record your observations and inferences in the spaces provided.

i)Place half a spatulaful of solid F in a non-luminous flame to ignite.

Observations	Inference
-melt -burns with yellow sooty flame

ii)Place the rest of the solid in a test-tube. Add about 6cm³ of distilled water and shake the mixture well. Divide the solution into 3 portions 

iii)To about 2cm3 of the solution, add a spatulaful of sodium hydrogen carbonate.

iv)To about 2cm³, add 2 drops of acidified potassium manganate (vii) solution.

Observations	Inference
purple H+KMnO4 decolourised

v)To another 2cm³, add 2 drops of bromine water.

Observations	Inference
yellow bromine water decolourised

CONFIDENTIAL

In addition to the apparatus and the fittings found in the chemistry laboratory, each candidate will require the following.

1. One Burette, 0-50ml.
2. One 25ml Pipette.
3. Two 250ml Conical Flask
4. One complete Retort Stand
5. One White Tile
6. One Pipette Filler
7. Six Test-tubes
8. Two Boiling tubes
9. Wash bottle filled with distilled water
10. One metallic spatula.
11. About 1g of solid sodium hydrogen carbonate.
12. Thermometer
13. 120cm³ solution A.
14. 120cm³solution B.
15. Distilled water in a wash bottle.
16. Solid R.
17. Solid Q.
18. Solid F.

ACCESS TO

1. Source of heat.
2. Acidified Potassium Manganite (VII)
3. Bromine water
4. Sodium sulphate solution
5. Aqueous sodium hydroxide solution.
6. Aqueous ammonia solution
7. Acidified barium nitrate solution

NOTES

• Solid R is 2.0g Potassium chlorate, KClO₃
• Solution A is prepared by dissolving exactly 39.2g of FeSO₄(NH₄)₂SO₄.nH₂O in 600cm³ of distilled water and dilute with distilled water to one litre.
• Solution B is prepared by dissolving 3.0g of KMnO₄ in 400ml of 2M H₂SO₄ and diluting with distilled water to one litre.