Chemistry Paper 3 Questions and Answers with Confidential - Bungoma Diocese Mock Exams 2021/2022

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INSTRUCTIONS TO THE CANDIDATES:-

  • Answer all the questions in the spaces provided.
  • Mathematical tables and electronic calculators may be used.
  • All working MUST be clearly shown where necessary.
  • Use the first 15minutes of the 2 hours to ascertain you have all the chemicals and apparatus tha you may need.
  1. You are provided with;
    • Solution K, hydrochloric acid
    • Solution L, containing 2g per litre of sodium hydroxide.
    • 0.5 g of an impure calcium carbonate, solid N.
    • You are required to determine the :
      1. Concentration of solution K in moles per litre.
      2. Percentage purity of calcium carbonate, solid N

        Procedure I
        Fill the burette with hydrochloric acid, solution K. pipette 25cm3 of sodium hydroxide, solution L into a conical flask. Add 2-3 drops of phenolphthalein indicator and titrate. Record the results in the table. Repeat the procedure two more times.
        Table I
           I   II   III 
         Final burette reading (cm3      
         Initial burette reading (cm3      
         Volume of solution K used (cm3)      
        4mks
        1. What is the average volume of solution K used (1mk)
        2. Determine the concentration of solution L in moles per litre. (1mk( Na= 23,O = 16, H = 1)
        3. Determine the number of moles of solution L that reacted with solution K(1mk)
        4. Write the equation of the reaction that took place( 1mk)
        5. Calculate the number of moles of solution K that reacted( 1mk)
        6. Calculate the concentration of solution K in moles per litre. (1mk)

          Procedure II
          Using a measuring cylinder, measure out 100cm3 of solid K into a 250ml beaker. Add all of solid N into the beaker containing solution K. Swirl the mixture and allow the reaction to proceed until offervescence stops. Label this as solution P. Fill the burette with solution P. pipette 25cm3 of solution L into a conical flask. Add 2-3 drops of phenolhthalein indicator and titrate. Record your results in table II below repeat the titration two more times and complete the table
          Table II
             I   II   III 
           Final burette reading (cm3      
           Initial burette reading (cm3      
           Volume of solution K used (cm3)      
          4 mks
          1. Determine the average volume of solution P used. 1mk
          2. Calculate the number of moles of hydrochloric acid in solution P used. (1mk)
          3. Determine the number of moles of hydrochloric acid in 100cm3 of solution P. (1mk)
          4. Calculate the:
            1. Moles of hydrochloric acid in 100cm3 of the original hydrochloric acid solution K (1mk)
            2. Moles of the hydrochloric acid that were used up in the reaction with solid N. (1mk
            3. Moles of calcium carbonate that reacted with hydrochloric acid.(1mk)
          5. Given that the relative formula mass of calcium carbonate is 100,calculate the:
            1. Mass of the calcium carbonate that reacted. (1mk)
            2. Percentage purity of the calcium carbonate, solid N. (1mk)
  2. You are provided with solid T. Carry out the following tests and write your observations and inferences in the spaces provided.
    Place all solid T in a boiling tube. Add about 6cm3 of distilled water to the solid T and shake the mixture well. Retain the mixture for use in the following tests.
    1. Dip a clean glass rod in the mixture obtained above and burn it on a Bunsen burner flame.
       Observation   Inference 
                (1mark)         (1 mark) 
    2. Divide the mixture in the boiling tube into 3 portions.
      1. To the 1st portion, add about 1cm3 of barium chloride solution. Retain the resulting mixture for use in (iii) below.
         Observation   Inference 
                  (1mark)         (1 mark) 
      2. To the mixture in (ii) above, add about 4cm3 of dilute hydrochloric acid.
         Observation   Inference 
                  (1mark)         (1 mark) 
      3. To the 3rd portion, add about 3 drops of acidified potassium manganate (VII) solution.
         Observation   Inference 
                  (1mark)         (1 mark) 
  3. You are provided with solid J. Carry out the test below to identify the compound.
    1. Place ½ spatula of solid J in a hard test tube and heat strongly until no further change. Test the gas produced with litmus paper.
       Observation   Inference 
                (½ mark)         (½ mark) 
    2. Place the remaining solid J into a clean boiling tube. Half fill it with distilled water and shake well. Divide the solution into four portions.
      1. To the first portion add dilute sodium hydroxide solution dropwise till in excess.
         Observation   Inference 
                  (1mark)         (1 mark) 
      2. To the second portion add ammonia solution dropwise till in excess.
         Observation   Inference 
                  (1mark)         (1 mark) 
      3. To the third portion add drops of dilute barium nitrate.
         Observation   Inference 
                  (1mark)         (1 mark) 
      4. To the fourth portion add a few drops of dilute nitric acid followed by lead (II) nitrate solution and warm.
         Observation   Inference 
                  (1mark)         (1 mark) 
        Identify Compound J……………………………………….… (1 mark)

CONFIDENTIAL

Question one.

  • Burette
  • Pipette
  • Filter Funnel
  • Retort stand and clamp
  • Conical flask, 250ml
  • White tile
  • Phenolphthalein indicator
  • 100cm3 of Solution K, 0.1M hydrochloric acid
  • 100cm3 OF Solution L 2g per litre of sodium hydroxide.
  • Solid N 0.5 g of an impure calcium carbonate, ( N is made by mixing CaCO3 and Sodium Chloride in the ratio 4:1)
  • An empty 250ml beaker

Question two and three

  • Solid T sodium sulphite
  • Solid J mixture of ammonium sulphate and hydrated zinc sulphate ratio 1:1
    Access to
  • Distilled water in wash bottle
  • Barium chloride solution
  • 2M hydrochloric acid
  • Acidified potassium manganate vii
  • Source of heating
  • Barium nitrate
  • 2M nitric v acid
  • Lead ii nitrate
  • 2M NaOH
  • Aqueous ammonia solution
  • Litmus papers


MARKING SCHEME

  1. Procedure I 
    1.  
    2. 2/40 = 0.05 moles
    3. 0.05 → 1000
              →  25
      25 × 0.05 = 0.00125
         1000
    4. NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) 
    5. Ratio 1:1 ancs c = 0.00125
    6. 0.00125 → ans (a)
                    ← 1000
      1000 × 0.00125
              Ans (a)
      Procedure II
      1.  
      2. Moles of NaOH ,L, which reacted HCl(=P) = 25 × 0.05
                                                                                  1000
      3. Average Titre of sol P contains 0.00125 moles of HCl
             100cm3   = 100 × 0.00125
                                   Ave. titre
      4.  
        1. Procedure (I) × answer F × 100
                             1000
        2. Answer d(i) − Answer in (c)
        3. CaCO3 + 2HCl → CaCl2 + CO2 + H2O = answer d(ii)
                      Ratio 1:2                                              2
      5.  
        1. Ans a(III) × 100
                    1
        2. Answer a(I) × 100
                     0.5
  2. You are provided with solid T. Carry out the following tests and write your observations and inferences in the spaces provided.
    Place all solid T in a boiling tube. Add about 6cm3 of distilled water to the solid T and shake the mixture well. Retain the mixture for use in the following tests.
    1. Dip a clean glass rod in the mixture obtained above and burn it on a Bunsen burner flame.
       Observation   Inference 
       Burns with a yellow flame         (1mark)    Na+ present     (1 mark) 
    2. Divide the mixture in the boiling tube into 3 portions.
      1. To the 1st portion, add about 1cm3 of barium chloride solution. Retain the resulting mixture for use in (iii) below.
         Observation   Inference 
         White ppt formed         (1mark)    SO42−, SO32−, CO32−     (1 mark) 
      2. To the mixture in (ii) above, add about 4cm3 of dilute hydrochloric acid.
         Observation   Inference 
         White ppt dissolves         (1mark)   SO32−, CO32− present      (1 mark) 
      3. To the 3rd portion, add about 3 drops of acidified potassium manganate (VII) solution.
         Observation   Inference 
         Acidified K2Cr2O7 changes from orange to green        (1mark)   SO32− present      (1 mark) 
  3.  
    1.  
       Observation   Inference 
       A gas is given out which turns blue litmus paper red         (½ mark)   SO42−  CO32− present  (½ mark) 
    2.  
      1.   
         Observation   Inference 
         White ppt is formed which dissolves in addition of exess.         (1mark)   Al3+, Zn2+,Pb2+  present      (1 mark) 
      2.  
         Observation   Inference 
         White ppt is formed which dissolves in addition of exess.         (1mark)   Zn2+ present      (1 mark) 
      3.  
         Observation   Inference 
         White ppt is formed.       (1mark)   SO42− present     (1 mark) 
      4.  
         Observation   Inference 
         White ppt is formed which dissolves in addition of exess.          (1mark)   SO42− present/ SO32− absent
             (1 mark) 

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