Chemistry Paper 3 Questions and Answers - Sukellemo Joint Mock 2020/2021

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SUKELLEMO JOINT MOCK
Kenya Certificate of Secondary Education
CHEMISTRY PAPER 3
(PRACTICAL)

2 hours 15 minutes

Instructions to Candidates

  • Answer all the questions in the spaces provided.
  • All working must be clearly shown.
  • Non-programmable silent electronic calculators and KNEC mathematical tables may be used.

Question One

You are provided with

  • Aqueous sulphuric VI acid labelled solution A
  • Solution B containing 8.0 g per litre of sodium carbonate
  • An aqueous solution of substance C, labelled solution C

You are required to determine the:

  • Concentration of solution A
  • Enthalpy of reaction between sulphuric VI acid and substance C

PROCEDURE

  1. Using a pipette and a pipette filler, place 25.0 cm3 of solution A into a 250ml volumetric flask. Add distilled water to make 250cm3 of solution. Label this solution D. Fill the burette with solution D. Clean the pipette and use it to place 25cm3 of solution B into a conical flask, then add 2 drops of methyl orange indicator provided and then titrate with solution D. Record your results in table 1. Repeat the titration 2 more times and complete the table.
       1  2
    Final burette reading (cm3      
    Initial burette reading (cm3)      
     Volume of solution D used(cm3)      
    Calculate the:
    1. Average volume of solution D used. ( 1 mark)
    2. Concentration of sodium carbonate in solution B. ( Na = 23, O =16, C=12).( 1mark)
    3. Concentration of sulphuric VI acid in solution D. ( 2 marks)
    4. concentration of sulphuric VI acid in solution A ( 2 marks)

  2. Label six test tubes as 1,2,3,4,5 and 6. Empty the burette, clean and fill it with solution A. From the burette, place 2cm3 of solution A into test tube number 1, from the same burette place 4cm3 of solution A into test tube number 2. Repeat the process for test tube numbers 3,4,5 and 6 as shown in table 2. Clean the burette and fill it with solution C. From the burette, place 14 cm3 of solution C into a boiling tube. Measure the initial temperature of solution C and record it in table 2. Add contents of test tube number 1 to the boiling tube containing solution C. Stir the mixture with the thermometer. Note and record the highest temperature reached in table 2. Repeat the process with the other volumes of solution C given in table 2 and complete the table
    Table 2
    Test tube number
    Test tube number   1  3  4  5
     Volume of solution A(cm3)  2  4  6  8  10  12
     Volume of solution C(cm3)  14  12  10  4
     Initial tempertue of solution (ºC)            
     Hihets tempoerature of mixture(ºC)            
     Change in temperature (ºC)            
    ( 6 marks)
    1. On the grid provided, draw a graph of ΔT (vertical axis) against volume of solution A used.( 3marks)
    2. From the graph, determine:
      1. The maximum change in temperature ( 1 mark)
      2. The volume of solution A required to give the maximum change in temperature.( 1 mark)
    3. Calculate the :
      1. Number of moles of sulphuric VI acid required to give the maximum change in temperature. ( 1 mark)
      2. Molar enthalpy of reaction between sulphuric VI acid and substance C , in kiloJoules per mole of sulphuric VI acid used.
        ( Assume the specific heat capacity of the solution is 4.2 J/g/K and density of the solution is 1g/cm3) ( 2 marks)

Question Two.

You are provided with solid Y. Carry out the following tests and write observations and inferences in the spaces provided.

  1. Place about one half of solid Y in a dry test tube and heat it strongly. Test any gas produced using blue and red litmus papers.
    Observation  Inference 
       
  2. Place the rest of solid Y in a boiling tube. Add about 10cm3 of distilled water. Shake well and use 2cm3 portions for each of the tests below.
    1. To one portion add aqueous ammonia dropwise until excess.
      Observation  Inference 
         
    2. To the second portion add 1cm3 of hydrochloric acid
      Observation  Inference 
         
    3. To the third portion, add two drops of lead (II) nitrate and heat the mixture to boiling.
      Observation  Inference 
         

Question Three
You are provided with an organic compound solid Z. Carry out the following tests. Record the observations and inferences in the spaces provided,

  1. Place all solid Z in a boiling tube. Add about 10cm3 of distilled water and shake. Retain the solution for use in procedure (b) (i), (ii) and (iii)
    Observation  Inference 
       


  2. Use about 2cm3 portions of the mixture in a test tube for tests (i), (ii) and (iii)
    1. To the first portion, add all the sodium carbonate provided.
      Observation  Inference 
         
    2. To the second portion, add two drops of acidified potassium manganate (VII) and warm the mixture
      Observation  Inference 
         
    3. To the third portion, add about 2cm3 of acidified Potassium dichromate (VI) , heat the mixture to boiling and allow to stand for 2 minutes.
      Observation  Inference 
         

CONFIDENTIAL

Sukellemo Chemistry paper 3

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

  1. About 120cm3 of solution A
  2. About 120cm3 of solution B
  3. About 100cm3 of solution C
  4. One pipette 25.0 ml
  5. One pipette filler
  6. One volumetric flask 250ml
  7. One burette 0-50ml
  8. Two conical flasks
  9. 8 clean dry test tubes
  10. Test tube rack
  11. One thermometer -10 to 1100 C
  12. Two boiling tubes
  13. About 0.5g of solid Y
  14. About o.5g of solid Z
  15. One blue and one red litmus paper
  16. One 10ml measuring cylinder
  17. About 500cm3 of distilled water in a wash bottle
  18. One test tube holder
  19. About 0.2g of solid sodium carbornate
  20. One blue and one red litmus papers
  21. One spatula
  22.  7 labels

Access to

  1. Methyl orange indicator
  2. Burnsen burner
  3. 2M aqeous ammonia supplied with a dropper
  4. 0.05M lead II nitrate solution supplied with a dropper
  5. 2M aqeous hydrochloric acid supplied with a dropper
  6. Acidified potassium manganate (VII) supplied with a drpper
  7. Acidified potassium dichromate (VI) supplied with a dropper.
  8. Bunsen burner

Preparations

  1. Solution A is prepared by dissolving 50cm3 of 1.84g/cm3 (98%) cocentrated sulphuric VI acid in about 600cm3 of distilled water and diluting to one litre of solution.
  2. Solution B is prepared by dissolving 8.0g of anhydrous sodium carbonate in about 500cm3 of distilled water and diluting to one litre of solution.
  3. Solution C is prepared by dissolving 60.0g of sodium hydroxide pellets in about 700cm3 of distilled water and diluting to one litre.
  4. Acidified potassium dichromate VI is prepared by dissolving 25g of solid Potassium dichromate in 200cm3 of 2M Sulphuric VI acid and diluting with distilled water to make one litre of solution
  5. Acidified Potassium manganate ( VII) is prepared by dissolving 3.2g of solid Potassium manganate ( VII) in 200cm3 in 200cm3 of 2M sulphuric ( VI) acid d diluting with distilled water to make one litre of solution.
  6. Solid Y is a mixture of ammonium sulphate and hydrated aluminium sulphate in the ratio 1:1
  7. Solid Z is glucose

MARKING SCHEME

Question One

You are provided with

  • Aqueous sulphuric VI acid labelled solution A
  • Solution B containing 8.0 g per litre of sodium carbonate
  • An aqueous solution of substance C, labelled solution C

You are required to determine the:

  • Concentration of solution A
  • Enthalpy of reaction between sulphuric VI acid and substance C

PROCEDURE

  1. Using a pipette and a pipette filler, place 25.0 cm3 of solution A into a 250ml volumetric flask. Add distilled water to make 250cm3 of solution. Label this solution D. Fill the burette with solution D. Clean the pipette and use it to place 25cm3 of solution B into a conical flask, then add 2 drops of methyl orange indicator provided and then titrate with solution D. Record your results in table 1. Repeat the titration 2 more times and complete the table.
       1  2
    Final burette reading (cm3 18.1   18.1  18.1
    Initial burette reading (cm3) 0.0   0.0  0.0
     Volume of solution D used(cm3)  18.1  18.1  18.1

    Complete table - 1 mk
    Decimal - 1/2 mk
    Accuracy - 1 mk
    Principles of averaging - 1 mk
    Final answer - 1/2mk
    Total 4 marks

    Calculate the:
    1. Average volume of solution D used. ( 1 mark)

      (18.1+18.1+18.1)/3
      = 18.1 cm3

    2. Concentration of sodium carbonate in solution B. ( Na = 23, O =16, C=12).( 1mark)

      RFM of Na2CO3 = 106
      8/106
      = 0.0754717 M

    3. Concentration of sulphuric VI acid in solution D. ( 2 marks)

      Na2CO3 (aq) + H2SO4 (aq) → Na2SO4 (aq) + CO2 (aq) + H2O (l)
      Moles of Na2CO3 used = (25/1000) * 0.0754717 = 0.00188679
      Moles of sulphuric acid in soln D = 0.00188679
      18.1 cm3 contains 0.00188679 moles
      1000 cm3 contains (1000/18.1)* 0.00188679
      = 0.10424254 M

    4. concentration of sulphuric VI acid in solution A ( 2 marks)

      moles of acid in 250cm3soln D = moles of acid in 25cm3of soln A
      = 250/1000 * 0.10424245= 0.02606064
      Molarity = (1000/25)* 0.02606064= 1.0424M

  2. Label six test tubes as 1,2,3,4,5 and 6. Empty the burette, clean and fill it with solution A. From the burette, place 2cm3 of solution A into test tube number 1, from the same burette place 4cm3 of solution A into test tube number 2. Repeat the process for test tube numbers 3,4,5 and 6 as shown in table 2. Clean the burette and fill it with solution C. From the burette, place 14 cm3 of solution C into a boiling tube. Measure the initial temperature of solution C and record it in table 2. Add contents of test tube number 1 to the boiling tube containing solution C. Stir the mixture with the thermometer. Note and record the highest temperature reached in table 2. Repeat the process with the other volumes of solution C given in table 2 and complete the table
    Table 2

    Test tube number   1  3  4  5
     Volume of solution A(cm3)  2  4  6  8  10  12
     Volume of solution C(cm3)  14  12  10  4
     Initial tempertue of solution (ºC)  22.0  22.0  22.0 22.0  22.0  22.0
     Hihets tempoerature of mixture(ºC)  24.0  28.0  31.0  31.0  28.0  26.0
     Change in temperature (ºC)  2.0  6.0  9.0  9.0  6.0  4.0
    ( 6 marks)

    Complete table - 3mks
    Decimal - 1 mk
    Accuracy - 1 mk
    Trend - 1 mk continuous rise in temperature of mixture ½ mk followed by a constant then continuous decrease/ or continuous decrease


    1. On the grid provided, draw a graph of ΔT (vertical axis) against volume of solution A used.( 3marks)
    2. From the graph, determine:
      1. The maximum change in temperature ( 1 mark)
        105ºC
        • Correct value of ΔT from a correctly extrapolated graph with showing----1 mk
        • Award 1/2mk for correct showing on an extrapolated graph even if the reading of ΔT is missing
      2. The volume of solution A required to give the maximum change in temperature.( 1 mark)
        6.8 cm3
        • Correct value of V from a correctly extrapolated gragh-------1 mark
        • Award ½ mk for correct showing on an extrapolated gragh even if the reading is missing

    3. Calculate the :
      1. Number of moles of sulphuric VI acid required to give the maximum change in temperature. ( 1 mark)

        (6.8/1000) * 1.0424 - ½ mk
        = 0.00708832 - ½ mk

      2. Molar enthalpy of reaction between sulphuric VI acid and substance C , in kiloJoules per mole of sulphuric VI acid used.
        ( Assume the specific heat capacity of the solution is 4.2 J/g/K and density of the solution is 1g/cm3) ( 2 marks)
        • Heat evolved = 16*4.2*10.5
          = 704.6 J or 0.7046 kJ - ½ mk
          0.00708832 →0.7046 kJ
          1 mole →(0.7046/0.00708832) - 1mk
          = - 99.402965 ½ mk

Question Two.

You are provided with solid Y. Carry out the following tests and write observations and inferences in the spaces provided.

  • Place about one half of solid Y in a dry test tube and heat it strongly. Test any gas produced using blue and red litmus papers.
    Observation  Inference 
    -Colourless liquid formed on the cooler parts of the test tube ½ mk
    -Colourless gas with pungent smell ½ mk
    -Red litmus turns blue ½ mk
    -Blue litmus remains blue ½ mk
    -Hydrated compound ½ mk
    -NH4+ present ½ mk
  • Place the rest of solid Y in a boiling tube. Add about 10cm3 of distilled water. Shake well and use 2cm3 portions for each of the tests below.
    1. To one portion add aqueous ammonia dropwise until excess.
      Observation  Inference 
       -White precipitate insoluble in excess

      1 mark

      Al3+ , Pb2+, Mg2+ present

      1 mark

    2. To the second portion add 1cm3 of hydrochloric acid
      Observation  Inference 

      -No white precipitate

      -No bubbles

      1 mark

      Mg2+ Al3+ present 1mk 
      award Pb2+ absent ½ mk
      SO32-, CO32-absent 1mk

      2 marks

    3. To the third portion, add two drops of lead (II) nitrate and heat the mixture to boiling.
      Observation  Inference 
      -White precipitate

      1 mark

       

      SO42-present
      1 mark

Question Three
You are provided with an organic compound solid Z. Carry out the following tests. Record the observations and inferences in the spaces provided,

  1. Place all solid Z in a boiling tube. Add about 10cm3 of distilled water and shake. Retain the solution for use in procedure (b) (i), (ii) and (iii)
    Observation  Inference 
    -Dissolves to form a colourless solution

    1 mark

    Polar compound
  2. Use about 2cm3 portions of the mixture in a test tube for tests (i), (ii) and (iii)
    1. To the first portion, add all the sodium carbonate provided.
      Observation  Inference 
      -No effervessence

      1 mark

      RCOOH absent

      Award ½ mk for H+absent
      1 mark

    2. To the second portion, add two drops of acidified potassium manganate (VII) and warm the mixture
      Observation  Inference 
      -Purple H/KMnO4 turns colourless

      1 mark

       C C / C C ½ mk
      And
      ROH present ½ mk

      1mark

    3. To the third portion, add about 2cm3 of acidified Potassium dichromate (VI) , heat the mixture to boiling and allow to stand for 2 minutes.
      Observation  Inference 
      -Orange H/K2CrO7 turns green (1 mark) ROH present (1 mark)

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