Chemistry Paper 3 Questions and Answers - Pavement Pre-Mock Exams 2021/2022

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Question 1
You are provided with:

  • Solution A – containing 21.2g per litre of anhydrous sodium carbonate (Na2CO3(s))
  • Solution B – Nitric (V) acid solution
  • Solution C – metal hydroxide M(OH)x

Procedure I

  1. Fill the burette with solution B
  2. Using a pipette, transfer 25cm3 of solution A into a clean conical flask and add 1-2 drops of methyl orange indicator.
  3. Titrate with solution B from burette.
  4. Repeat the titration to obtain accurate results and record the data in the table below.    (4 marks)
    Table I
     Titre   I   II   III 
     Final burette reading (cm3      
     Initial burette reading (cm3      
     Volume of solution B used (cm3      
    1. Find the average volume of solution B used. (1 mark)
    2. Given that the equation for the reaction is
      Na2CO3(aq) + HNO3(aq)  →  NaNO3(aq) + H2O(l) + CO2(g)
      Calculate;
      1. The number of moles of sodium carbonate in 25cm3 of solution A (3 marks)
      2. The number of moles of the acid in the titre volume obtained. (1 mark)
    3. Hence find the molarity of nitric (V) acid solution B. (1 mark)

Procedure II

  1. Pipette 25cm3 of solution C into a clean conical flask.
  2. Add 1-2 drops of methyl orange indicator.
  3. Titrate with solution b.
  4. Repeat the titration to obtain accurate results and fill the table below.    (4 marks)
    Table II
     Titre   I   II   III 
     Final burette reading (cm3      
     Initial burette reading (cm3      
     Volume of solution B used (cm3      
    1. Find the average titre volume of solution B used. (1 mark)
    2. Determine the equation for the reaction between the hydroxide M(OH)x and nitric (V) acid. (2marks)
    3. What is the value of x in M(OH)x ? (1 mark)

Question 2

You are provided with solid Q. carry out the following tests below.

  1. Transfer all of the solid Q into a boiling tube. Add about 6cm3 of distilled water and shake the mixture thoroughly. Allow in to settle and then carefully filter into another boiling tube. RETAIN THE RESIDUE FOR PART B.
    divide the filtrate into 3 portions
    1. To the first filtrate, add a few drops of lead ii nitrate solution and warm.
       Observation (1mark)   Inference (½ mark) 
         
    2. To the second portion, add sodium hydroxide, dropwise and in excess.
       Observation (1mark)   Inference (½ mark) 
         
    3. Describe how you would carry out a flame test on the third portion. Proceed and give expected observations.
       Observation (1mark)   Expected Observation (½ mark) 
         
    4. On the third portion, carry out a flame test as suggested above
       Observation (1mark)   Inference (½ mark) 
         
  2. To the residue in a boiling tube add 2M hydrochloric acid provided drop wise until there is no more change. Test for any gas using a burning splint.
    1. Divide the resultant solution into two portions.
       Observation (1mark)   Inference (½ mark) 
         
    2. To the first portion, add 2M sodium hydroxide solution drop wise until in excess.
       Observation (1mark)   Inference (½ mark) 
         
    3. To the second portion, add 2M ammonium hydroxide solution until in excess.
       Observation (1mark)   Inference (½ mark) 
         

Question 3

You are provided with:

Solid W
Bromine water
Acidified potassium manganate (VII)
Sodium carbonate

Solid W is suspected to be an organic compound.

  1. Using the reagents provided describe the tests that could be performed consecutively to confirm which type of organic compound is Solid W. Record the tests and expected observations in the spaces provided.
    1.  
       Test 1       Expected Observatons 
         
         
         
         
       (1 mark)        (1 mark)
    2.  
       Test 2       Expected Observatons 
         
         
         
         
       (1 mark)        (1 mark)
    3.  
       Test 3       Expected Observatons 
         
         
         
         
       (1 mark)        (1 mark)
  2. Carry out the tests described in (a) above using solid W and record the observations and inferences in the spaces provided.
    1. Test 1 
       Observations       Inferences 
         
         
         
         
       (1 mark)        (1 mark)
    2. Test 2 
       Observations       Inferences 
         
         
         
         
       (1 mark)        (1 mark)
    3. Test 3
       Observations       Inferences 
         
         
         
         
       (1 mark)        (1 mark) 

CONFIDENTIAL

  1. Burette
  2. Pipette
  3. Two conical flasks
  4. 10 ml measuring cylinder
  5. Funnel
  6. Phenolphthalein indicator
  7. Universal indicator
  8. Solution H – 100 cm3 0.02 M acidified potassium manganate (VII)
  9. Solution M 100cm3
  10. Solid Z
  11. Distilled water in wash bottle
  12. 250 ml glass beaker
  13. Stop watch or wrist watch
  14. 6 test tubes on a test tube rack
  15. One boiling tube
  16. Solid W (one spatula full)
  17. Solid B (one spatula full)
  18. 2M aqueous ammonia bench solution
  19. Means of heating
  20. Metallic spatula
  21. 0.1 M Ba(NO3)2 bench solution
  22. 0.1 M acidified potassium manganate (VII) bench solution
  23. 0.1 M acidified potassium dichromate (VI) bench solution
  24. 2M HCl bench solution

Notes on preparations:-

  • Solution M made by dissolving 1.0 g of sodium hydroxide in 250 ml of distilled water.
  • Solution H – 100 cm3 0.02 M acidified potassium manganate (VII)
  • Solid W = sodium sulphite
  • Solid B = Carboxylic acid (oxalic)
  • Solid Z = 1.60 g of oxalic acid
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