Chemistry P3 Questions and Answers - Wisdom Pre-Mock Form 4 Exams 2021/2022

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Instructions to Candidates

  1. Write your name and ADMISSION numbers in the spaces provided above.
  2. Sign and write the date of examination in the spaces provided above.
  3. Answer ALL the questions in the spaces provided in the question paper.
  4. Mathematical tables and silent electronic calculators may be used.
  5. All working MUST be clearly shown where necessary.
  6. Candidates should check the question paper to ascertain that all pages are printed as indicated and that no questions are missing.

For Examiner’s Use Only

Question

Maximum Score

Candidate’s Score

1

20

 

2

10

 

3

10

 

TOTAL SCORE

40

 



Question 

  1. (20 marks) You are provided with:
    • Solution P, hydrochloric acid
    • Solution Q, containing 8.8g per litre of sodium hydroxide.
    • 0.6g of an impure carbonate, solid B
      You are required to determine the:
      1. Concentration of solution P in moles per litre.
      2. Percentage purity of the carbonate, solid B.

Procedure I
Fill the burette with sodium hydroxide, solution Q. Pipette 25.0cm3 of hydrochloric acid, solution P into a conical flask. Add 2 – 3 drops of methyl orange indicator and titrate. (The colour of the indicator changes from pink to yellow). Record your results in table 1 below. Repeat the titration two more times and complete the table.
Table I

 

I

II

III

Final burette reading

     

Initial burette reading

     

Volume of solution Q used (cm3)

 

 

 

(4 marks)

  1. What is the average volume of solution Q used? (1 mark)
  2. Determine the:
    1. Concentration of solution Q in moles per litre. (Na = 23.0; O = 16.0, H = 1.0) (1 mark)
    2. Concentration of solution P in mole per litre (2 marks)

Procedure II
Using a 100ml measuring cylinder, measure out 100cm3 of solution P into a 250cm3 beaker.
Add all of solid B into the beaker containing solution P. Swirl the mixture and allow the reaction to proceed for about 4 minutes.
Label the solution obtained here as solution K.
Fill the burette with sodium hydroxide, solution Q. Pipette 25.0cm3 of solution K into a conical flask. Add 2- 3 drops of methyl orange 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

     

Initial burette reading

     

Volume of solution Q (cm3)

     

(4 marks)
c) What is the average volume of solution Q used? (1 mark)
d) Calculate the :

  1. Moles of hydrochloric acid in 25.0cm3 of solution K. (1 mark)
  2. Moles of hydrochloric acid in 100cm3 of solution K. (1 mark)
  3. Moles of hydrochloric acid in 100cm3 of the original hydrochloric acid solution P. (1 mark)
  4. Moles of hydrochloric acid that were used up in the reaction with solid B. (1 mark)
  5. Moles of the carbonate that reacted with hydrochloric acid. (1 mark)

e) Given that the relative formula mass of the carbonate is 72, calculate the:

  1. Mass of the carbonate that reacted. (1 mark)
  2. Percentage purity of the carbonate, solid B. (1 mark)

2. (10marks) You are provided with solid M. Carry out the tests below and record your observations and inferences in the spaces provided.

  1. Place all of solid M in a boiling tube and add about 10cm3 distilled water and shake.
    Observations (½mark)
    Inferences (½mark)
  2. Divide the solution into five portions of about 2cm3 each.
    1. To the first portion, add aqueous sodium hydroxide dropwise until in excess.
      Observations (1mark)
      Inferences (1mark)
    2. To the second portion, add aqueous ammonia dropwise until in excess.
      Observations (1mark)
      Inferences (1mark)
    3. Dip a glass rod in the third portion and heat it on a burnsen burner flame, identify the colour of the flame produced.
      Observations (½mark)
      Inferences (½mark)
    4. To the fouth portion,add about 1cm3 of lead (II) nitrate solution.
      Observations (1mark)
      Inferences (1mark)
    5. To the fifth portion, add about 1cm3 of dilute sodium hydroxide followed by a small piece of aluminium foil. Warm the mixture gently and carefully. Test any gas produced using blue and red litmus papers.
      Observations (1mark)
      Inferences (1mark)

3. (10marks)You are provided with solid W. Carry out the tests below and record your observations and inferences in the spaces provided.

  1. Place about one third of solid W on a metallic spatula and burn it using a Bunsen burner.
    Observations (1mark)
    Inferences (1mark)
  2. Place the remaining solid W into a boiling tube. Add 10cm3 of distilled water and shake well. Use 2cm3 portions of the mixture for each of the following reactions.
    1. To the first portion, add 2 drops of acidified potassium manganate (VII) and shake well.
      Observations (1mark)
      Inferences (1mark)
    2. To the second portion, add three drops of bromine water
      Observations (1mark)
      Inferences (1mark)
    3. To the third portion put universal indicator paper.
      Observations (1mark)
      Inferences (1mark)
    4. To the fourth portion add a little solid Y, sodium hydrogen carbonate.
      Observations (½mark)
      Inferences (½mark)
    5. To the fifth portion add about 2cm3 of ethanol and warm the mixture.
      Observations (½mark)
      Inferences (½mark)


MARKING SCHEME

1. Table I

 

I

II

III

Final burette reading

23.9

24.0

24.1

Initial burette reading

0.0

0.0

0.0

Volume of solution Q used (cm3)

23.9

24.0

24.1

CT = 1
Dec = 1
Acc = 1
PA = 1
FA = 1
5 Marks

  1. What is the average volume of solution Q used?
    (23.9+24.0+24.1)=24.0 cm3
              3
  2. Determine the:
    1. Concentration of solution Q in moles per litre. (Na = 23.0; O = 16.0, H = 1.0) (1mark)
      (8.8)=0.22M
        40
    2. Concentration of solution P in mole per litre (2marks)
      (M1 V1)=1
      (M2 V2 ) 1
      (M1×25)=1
      (0.22×24) 1
      M1=(0.22×24)
                 25
      = 0.2112M

Table II

 

I

II

III

Final burette reading

12.4

12.5

12.6

Initial burette reading

0.0

0.0

0.0

Volume of solution Q (cm3)

12.4

12.5

12.6

CT = 1
Dec = 1
Acc = 1
PA = 1
FA = 1
5 Marks

c).What is the average volume of solution Q used?
(12.4+12.5+12.6)=12.5cm3
            3

d).Calculate the :

  1. Moles of hydrochloric acid in 25.0cm3 of solution K. (1mark)
    Moles of HCl in 25cm3 of A=moles of NaOH in 12.5cm3 of J
    (0.22×12.5)
        1000
    =0.00275moles
  2. Moles of hydrochloric acid in 100cm3 of solution K. (1mark)
    (0.00275×100)
              25
    =0.011moles
  3. Moles of hydrochloric acid in 100cm3 of the original hydrochloric acid solution P. (1mark)
    (0.2112×100)
         1000
    =0.02112moles
  4. Moles of hydrochloric acid that were used up in the reaction with solid B. (1mark)
    Ans a(iii)-a(ii)
    =0.02112-0.011
    =0.01012moles
  5. Moles of the carbonate that reacted with hydrochloric acid. (1mark)
    CO32-(aq) + 2H+(aq) → CO2(g) + H2O(l)
    (0.01012×1)=0.00506moles
           2
  6. Given that the relative formula mass of the carbonate is 72, calculate the:
    1. Mass of the carbonate that reacted. (1mark)
      (0.00506×72)=0.36432g
            1
    2. Percentage purity of the carbonate, solid B. (1mark)
      Percentage purity=(0.36432) ×100
                                         0.6

2. (10marks) You are provided with solid M. Carry out the tests below and record your observations and inferences in the spaces provided.

  1. Place all of solid M in a boiling tube and add about 10cm3 distilled water and shake.
    Observations 
    • Colourless solution (½mk)
    Inferences 
    • Cu2+, Fe2+, Fe3+ absent (½mk)
  2. Divide the solution into five portions of about 2cm3 each.
    1. To the first portion, add aqueous sodium hydroxide dropwise until in excess.
      Observations 
      • White ppt (½mk) insoluble in excess½mk
      Inferences 

      Ca2+, Mg2+, Ba2+present
      - All three/any two correct ions given 1 mk.
      - Only one correct ion given ½ mk.

    2. To the second portion, add aqueous ammonia dropwise until in excess.
      Observations 
      • White ppt (½mk) insoluble in excess½mk
      Inferences 

      Mg2+, Ba2+present
      - All two correct ions given 1 mk.
      - Only one correct ion given ½ mk.

    3. Dip a glass rod in the third portion and heat it on a burnsen burner flame, identify the colour of the flame produced.
      Observations 
      • Green flame (½mk)
      Inferences 

      Ba2+present  mk)

    4. To the fouth portion,add about 1cm3 of lead (II) nitrate solution.
      Observations 
      • No white ppt 1mk

      NOTE
      - Accept “No ppt”/”colourless solution retained”/ “No observable change” for½mk but accept CORRECT inference and credit accordingly
       - REJECT Colourless solution formed/No colour change/ No white substance/ No reaction/ No observation

      Inferences (1mark)

      SO42-, CO32-, SO32-absent
      - All 3 ions given 2mks
      - 2 ions given 1mk
      - 1 ion given ½ mk
      NOTE:
      - Where there is a contradictory ion mark out of 1½ mks and penalise ½ mk  for EACH contradictory ion given to a maximum of 1½ mks.
      - Accept correct ion(s) written in words for ½mk

    5. To the fifth portion, add about 1cm3 of dilute sodium hydroxide followed by a small piece of aluminium foil. Warm the mixture gently and carefully. Test any gas produced using blue and red litmus papers.
      Observations 

      Colourless gas (½mk) the turns red litmus blue and blue litmus remains blue (½mk)

      Inferences (1mark)

      NO3- present (1mk)

3. (10marks)You are provided with solid W. Carry out the tests below and record your observations and inferences in the spaces provided.

  1. Place about one third of solid W on a metallic spatula and burn it using a Bunsen burner.
    Observations 
    • Solid melts and burns with a yellow(½mk)/ luminous and sooty(½mk)/ smoky flame
    Inferences (1mark)
      Ι    Ι

    C = C  /   ̶ C ≡ C  ̶   present (1mk)
     Ι     Ι
    NOTE
    Accept either of the following given in words in place of the above structures for FULL credit.

    • Carbon to carbon double/ triple bond present /Unsaturated organic compound /Long chain organic compound /Aromatic compound /Organic compound with high Carbon-hydrogen ratio. (Reject C = C / C ≡ C)

    Ignore

    • Alkene / Alkyne present/Long chain hydrocarbon present.

    Penalize FULLY for any contradicting functional group given.

  2. Place the remaining solid W into a boiling tube. Add 10cm3 of distilled water and shake well. Use 2cm3 portions of the mixture for each of the following reactions.
    1. To the first portion, add 2 drops of acidified potassium manganate (VII) and shake well.
      Observations 
      • Acidified potassium manganate (VII) solution is decolourised OR Purple colour of acidified potassium manganate (VII) changes to colourless OR purple colour of acidified KMnO4 solution turns colourless.
      Inferences  
       Ι    Ι

      C = C  /   ̶ C ≡ C  ̶  
       Ι    Ι
      (½mk), R – OH (½mk)  present
      NOTE
      In absence of the above structures, accept the CORRECT inference given in words for FULL credit as “unsaturated organic compound and alcohol / alkanol present”.

    2. To the second portion, add three drops of bromine water
      Observations 
      • Yellow/ orange bromine is decolourised. (1mk)
      Inferences  
       Ι    Ι

      C = C  /   ̶ C ≡ C  ̶   present (1mk)
       Ι     Ι

    3. To the third portion put universal indicator paper.
      Observations 
      • pH=4 (1mk)
      • Accept pH = 5 or 6

      Reject pH given as a range

      Inferences 
      • Weakly acidic (1mk)

      Reject
      Weak acid/weak  alone

    4. To the fourth portion add a little solid Y, sodium hydrogen carbonate.
      Observations 

      Effervescence / Bubbles of a colourless gas / fizzing (½mk)
      NOTE
      Reject: hissing / fizzling / sizzling / “colourless gas” on its own
      Inferences 
      R – COOH present (½mk)
      NOTE
      Accept either of the following if given in place of the above structures for

      • carboxylic / alkanoic acid present
      • solution is acidic
      • H3O+ / H+ present
    5. To the fifth portion add about 2cm3 of ethanol and warm the mixture.
      Observations 

      Fruity / Pleasant smell (½mk)
      Reject :
      Sweet smell
      Inferences (½mark)
      R-COOH, -COOH present (½mk)
      (Accept for above in words for ½mk)
      Ester formed if R-COOH is not mentioned).
      N/B:
      Penalize fully for any contradictory functional group.



CONFIDENTIAL INFORMATION FOR THE CHEMISTRY PAPER

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

  1. 200cm3 of hydrochloric acid, solution P.
  2. 150cm3 of sodium hydroxide, solution Q.
  3. 50g of solid B weighed accurately.
  4. About 0.2g of solid Y.
  5. About 0.5g of solid M.
  6. About 0.5g of solid W.
  7. Burette 0-50 cm3.
  8. Pipette 25 cm3.
  9. One pipette filler
  10. Means of labeling (one label).
  11. 100 cm3 measuring cylinder.
  12. 10ml measuring cylinder
  13. 250 cm3
  14. Two conical flasks.
  15. Six dry test-tubes.
  16. About 1cm by 3cm aluminium foil
  17. 1 red and 1 blue litmus papers.
  18. Universal indicator paper
  19. About 2cm3 ethanol placed in a test tube
  20. 2 boiling tubes.
  21. Metallic spatula
  22.  Funnel
  23. A test-tube holder.
  24. Stop clock (wall clock)

BENCH REAGENTS/ ACCESS REAGENTS

  1. Methyl orange indicator – supplied with dropper
  2. Distilled water in a 500ml wash bottle
  3. 2M sodium hydroxide – supplied with dropper
  4. 2M aqueous ammonia – supplied with dropper
  5. 5M lead (II) nitrate solution – supplied with dropper
  6. Source of heat
  7. Universal indicator solution supplied with a dropper
  8. pH chart
  9. Acidified potassium manganate (VII) – supplied with a dropper
  10. Bromine water – supplied with a dropper

NOTES

  1. Solution P is prepared by adding 18.0cm3 (density=1.18g/cm3) of concentrated hydrochloric acid into 600cm3 of distilled water contained in a one litre volumetric flask and diluting to one litre of solution.
  2. Solution Q is prepared by dissolving 8.80g of sodium hydroxide in 600cm3 of distilled water contained in a one litre volumetric flask and diluting to one litre of solution. (22M)
  3. Acidified potassium manganate (VII) is prepared by dissolving 2.0g of potassium manganate (VII) provided in about 100cm3 of 2M sulphuric (VI) acid, adding 800cm3 of distilled water and diluting to one litre of solution. Label this as acidified potassium manganate (VII).
  4. Bromine water is prepared by adding 2ml of liquid bromine to 100cm3 of distilled water and the mixture stirred well in a fume cupboard.
  5. Solids :
    • B is Na2CO3
    • M is Ba(NO3)2
    • W is Maleic acid
    • Y is NaHCO3
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