Chemistry Paper 3 Questions and Answers with Confidential - Form 4 Mid Term 2 Exams 2021

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CHEMISTRY
PAPER 3
FORM 4 MID TERM 2

INSTRUCTIONS

  • Answer all questions
  1. QUESTION 1
    You are provided with:
    • Solution Q 0.125M Hydrochloric acid solution
    • N grammes of anhydrous sodium carbonate.
    • Methylorange indicator
      You are required to prepare a solution of sodium carbonate and then standardize it with hydrochloric acid solution Q.

      Procedure
    • Transfer all the N grams of sodium carbonate into a 250 ml volumetric flask.
    • Add 100cm3 of distilled water and shake till all the solid dissolves.
    • Add more distilled water upto the 250 ml mark and label it solution P. using a measuring cylinder, transfer 50cm3 of solution P into a clean 250 ml beaker and add 50cm3 of distilled water.
    • Stir well with a glass rod and label it solution T.
    • pipette 25.0cm3 of solution T and place it into a conical flask, add 2 drops of methyl orange indicator and titrate with solution Q from the burette. Record your results in the table 1 below and repeat the titration part to complete the table below.
      (3 mks)
        I II III
      Final burette reading (cm3)      
      Initial burette reading (cm3)       
      Volume of Q used (cm3)      

      1. Calculate the average volume of solution Q used. (1 mk)
      2.    
        1. Calculate the number of moles of solution Q used. (2 mks)
        2. Write an equation for the reaction between solution T and Q. (1 mk)
          Calculate:
        3. Number of moles of sodium carbonate solution in 25cm3 of solution T. (2 mks)
        4. Number of moles of sodium carbonate in 100cm3 of solution T. (2 mks)
        5. Number of moles of sodium carbonate in 50cm3 of the original solution P. (2 mks)
      3. Given that Na=23.0, C=12.0, O=16.0;
        1. The mass of sodium carbonate N grammes that were dissolved to make solution P. (1 mk)
        2. The concentration of sodium carbonate solution P in moles per litre. (2 mks)
  2. QUESTION 2
    You are provided with:
    • 1 M Sulphuric (vi) acid solution D.
    • 2 M Sodium hydroxide solution C.
      You are required to determine the heat of neutralization of Sulphuric (vi) acid solution D.

      Procedure
    • Measure 50cm3 of solution C and transfer into a 250cm3 plastic beaker provided. record the initial temperature of solution C.
    • measure 10cm3 of sulphuric(vi)acid solution D and add it to solution C in the beaker. Stir gently with the thermometer to mix and record the highest temperature in the table below.
    • Continue adding 10cm3 portions of solution D recording the temperature after each addition until 80cm3 of solution D has been added. (3 mks)
      Total volume of solution D added (cm3) 0 10 20 30 40 50 60 70 80
      Temperature of the mixture (ºC)                   

      1. Plot a graph of temperature against volume of sulphuric(vi)acid solution D added. (3 mks)
      2. From your graph determine the maximum temperature change ΔT. (1/2 mk)
      3. From your graph determine the volume of sulphuric(vi)acid solution required for neutralization.(1/2 mk)
      4. Calculate the molar heat of neutralization of 1M sulphuric(vi)acid solution D. (Assume density of water = 1g/cm3, specific heat capacity = 4.2 Jg-1K-1) (3 mks)
  3.                
    1. You are provided with solid A. carry out the following tests, record the observations and inferences.
      1. Place solid A in a boiling tube and add about 10cm3 of distilled water while shaking. Filter the solution and divide the filtrate into three portions. Keep the residue for part (b).
        Observation Inference
           

        1. To the first portion, add sodium hydroxide dropwise till in excess.
          Observation Inference
             
        2. To the second portion add 3 drops of barium nitrate solution.
          Observation Inference
             
        3. To the third portion add 3 drops of lead(ii)Nitrate solution
          Observation Inference
             
      2. Place the residue in(a) above in a boiling tube. Add dilute nitric(v)acid while shaking till the solid just dissolves.Divide the solution into two portions.
        Observation Inference
           
        1. To the first portion add sodium hydroxide solution dropwise till in excess.
          Observation Inference
             
        2. To the second portion, add a few drops of ammonia solution then in excess.
          Observation Inference
             
    2. You are provided with solid Z. carry out the tests below and record your observations and inferences. Place all of solid Z into a boiling tube. Add 10cm3 of distilled water and shake well. Divide the solution into three portions. 
      1. Test the first portion with both blue and red litmus paper.
        Observation Inference
           
      2. To the second portion add 2 drops of acidified potassium manganate(vii) and shake well.
        Observation Inference
           
      3. To the third portion add a little sodium hydrogen carbonate.
        Observation Inference
           

CONFIDENTIAL

In addition to the other common apparatus and reagents found in a chemistry laboratory, each candidate will require the following.

  1. About 100cm3 of 0.125M Hydrochloric acid labelled solution Q.
  2. Accurately weighed 2.65g of unhydrous sodium carbonate labeled solid N.
  3. 250ml volumetric flask.
  4. 100ml measuring cylinder.
  5. Distilled water
  6. 250 ml empty glass beaker
  7. Glass rod
  8. 1 label
  9. One burette (0-50ml)
  10. One 25.0 ml pipette
  11. Two conical flasks (250 ml)
  12. Methyl orange indicator
  13. Retort stand
  14. Pipette filler
  15. A white tile
  16. 6 dry test tubes
  17. 1 boiling tub
  18. One filter funnel
  19. 0-1100C thermometer
  20. 1 metallic spatula
  21. About 60cmof 1M Sulphuric(vi)acid labeled solution D.
  22. About 60cm3 of 2M sodium hydroxide solution labeled solution C.
  23. 250 ml plastic beaker empty.
  24. About 0.5g of solid Z.
  25. About 1.5g of solid A.
  26. 1 red and 1 blue litmus paper.
  27. About 0.2g of sodium hydrogen carbonate.
  28. 1 filter paper.

Access to:

  1. 2M NaOH with a dropper.
  2. 2M Ammonia solution with a dropper.
  3. 0.25M Barium nitrate solution with a dropper.
  4. 0.2M Lead (ii) nitrate solution with a dropper.
  5. 0.02M acidified Potassium Manganate (vii) with a dropper.
  6. 1M Nitric(v) acid.

NOTE:

  1. Solid A is a mixture of zinc carbonate and Sodium Sulphate in the ratio 1:1.
  2. Solid Z is oxalic acid.
  3. Solution Q is 0.125M Hydrochloric acid prepared by dissolving 10.75cm3 of concentrated hydrochloric acid in 1 litre.
  4. Solution D is 1M Sulphuric (vi) acid prepared by dissolving 55 cm3 of concentrated sulphuric (vi) acid in 1 litre of solution (Density of Sulphuric acid is 1.84 g/cm3).
  5. Solution C is 2M sodium hydroxide prepared by dissolving 80g of sodium hydroxide pellets in 1 litre of solution.
  6. 2 M Ammonia solution is prepared by dissolving 112cm3 of concentrated ammonia solution in 1 litre of solution.
  7. 0.25M Barium nitrate is prepared by dissolving 65g of Barium nitrate in 1 litre of solution.
  8. 0.2M lead(ii)nitrate is prepared by dissolving 66.2g of lead(ii)nitrate in a litre of solution.
  9.  1 M nitric acid is prepared by dissolving 64cm3 of concentrated Nitric(v) acid in 1 litre of solution.
  10. 0.02M acidified potassium manganate(vii) is prepared by dissolving 3.2g of the solid in 2.00cm3 of 2M sulphuric(vi) acid then diluting to 1 litre.

MARKING SCHEME

  1.    
    Table:
    • Award 1 mark for 3 titrations
    • Award 1/2 mark for only 2 titrations
    • Award 0 mk for 1 titration done
    • Decimal - 1mk
    • Accuracy 1mk 
      ± 0.2cm3 award 1/2 mk
      ± o.1cm3 award 1mk
      Total 3 mks
      1. Average volume of solution Q= 20.0cm3
      2.     
        1. moles of solution Q used
          20 x 0.125 = 0.0025 moles
             1000
        2. Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
        3. Moles of Na2CO3 in 25cm3 of solution T 
          1/2 x 0.0025 = 0.00125
        4. Moles of Na2CO3 in 100cm3 of solution T
          25cm3 → 0.00125moles
          then 100cm3 = 0.00125 x 100 = 0.005 moles
                                        25
        5. Moles of Na2CO3 in 50cm3 of the original solution P
          0.00moles → 100cm3 of T
                          → 250cm3
          250 x 0.005=0.025
             50
        6.     
        7. Mass of Na2CO3 in grammes
          =0.025 x 106g= 2.65g
        8. Concentration of Na2CO3 in solution P
          2.65 →250cm3
            ? → 1000cm3
          2.65 x 1000 = 10.6g/litre
             250
          Molarity= 10.6/106 = 0.1m
  2.  
      
    Total volume of solution D added (cm3) 0 10 20 30 40 50 60 70 80
    Temperature of the mixture (ºC)  240. 30.0 33.0 36.0 37.0 35.0 34.0 33.0 31.0

    CT 1 mk
    D.P - 1mk
    Temperature at 0 volume of solution D ± 2D
    1. Graph of temperature against volume of sulphuric (vi) acid added during neutralization reaction
      Labelled axis with units - 1mk
      plotting - 1mk
      Shape - 1mk
      Total - 3mks
    2. Temperature changes =- 13.0ºC
    3. Volume of H2SO4 required for neutralization 40cm3(1/2mk)
    4. Molar heat of neutralization
      Heat change= MCθ
      =(50 + 40) x 42 x 13J
      =90 x 42 x 13J= -4914J
      Moles of H2SO4 = 1 x 40= 0.04
                                   1000
      0.04 moles → -4914J
       1mole → ?
      -4.914 = 122.85KJ/mol
         0.04 
         
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  3.            
    1.     
      1.      
           
        Observation Inference
        - White residue
        - Colourless filtrate 
         Cu2+, Fe2+, Fe3+ present
         
        1.  
          Observation Inference
           No white ppt  Pb2+, Al 3+. Zn2+ absent 
          or
          K+ or Na+ present
             
        2.  
          Observation Inference
           White ppt formed  SO42-, SO32-, CO32- present
          (any two)
             
        3.    
          Observation Inference
          White ppt present  SO42- present
           
      2.    
        Observation Inference
        Effervesence, produces colourless gas  CO32- present 
         
        1.  
          Observation Inference
          White ppt which dissolves in excess  Pb2+, Al3+, Zn2+ present 
              
        2.    
          Observation Inference
          White ppt that dissolves in excess  Zn2+ present
            
    2.        
      1.    
        Observation Inference
         Blue litmus turns to red,
        red litmus remains red
         H+ present
          
      2.    
        Observation Inference
        Purple acidified potassium manganate (vii) is decolourised  |    |
        C = C
         |     |

        -C≡C-
        or 
        R-OH present
      3.  
        Observation Inference
         Effervesence present  H+ present
         

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