Chemistry Paper 3 Questions and Answers - Lanjet Joint Mock Exams 2022

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INSTRUCTIONS TO CANDIDATES

  • Write your name and index number in the spaces provided above.
  • Answer ALL the questions in the spaces provided.
  • You are not allowed to start working with the apparatus for the first 15 minutes of the 2¼ hours allowed time for the paper.
  • Use the 15 minutes to read through the question paper and note the chemicals you require
  • Mathematical tables and electronic calculators may be used.
  • All working MUST be clearly shown where necessary.

QUESTIONS

  1. You are provided with:
    • Dilute Sulphuric (vi) acid labeled solution A.
    • Solution B containing 8g/litres of anhydrous sodium carsonate.
    • Aqueous sodium hydrogen labeled solution C.
      You are required to determine:
    • Concentration of solution A in moles/litre.
    • Enthalpy of reaction between sulphuric (iv) acid solution A and solution C.
      Procedure
      1. Using a pipette, place 25cm3 of solution A into a clean 250cm3 volumetric flask then add distilled water to the mark to make it 250 cm3. Label this solution A1. Place solution A1 in the burette place 25cm3 of solution B into clean conical flask using pipette then 2 days of methyl orange indicator and titrate it using solution A1, from the burette and record your results in table 1 below. Repeat the titration two more times to complete table I. (4mks)
           I  II  III
         Find burette readings (cm3)      
         Initial burette readings      
         Volume of solution A1used      
        Calculate;
        1. Average volume of solution A1. (1mk)
        2. Concentration of solution B. (2mks)
          (Na = 23 O = 16 C= 12)
        3. Concentration of solution A1 that reacted with 25cm3 of solution B. (2mks)
        4. Concentration of sulphuric (iv) acid solution A. (2mks)
      2. Label six test tubes as 1, 2, 3, 4, 5 and 6. Empty burette 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 2.
        Respeat the procedure for test tube number 3, 4, 5 and 6 as shown in table below. Clean the burette and fill it with solution C. From the burette, place 14cm3 of solution C into boiling tube. Measure the initial temperature of solution C and record it in the table below. Add it to test tube number 1 to the boiling tube containing solution C. Stir the mixture with thermometer and note the highest temperature reached in table below. Repeat the procedure with other volumes of solution C given in table II below and complete it.
        Table II
         Test tube number   1  2  3  4  5  6
         Volume of solution A cm3  2  4  6  8  10  12
         Volume of solution C cm3  14  12  10  8  6  4
         Initial temperature of solution C (ºC)            
         Highest temperature of mixture (ºC)            
         Temperature charge ΔT (ºC)            
        (6mks)
        1. On the grid provided, plot the graph of temperature charge ΔT against volume of solution A used. (3mks)
        2. From the graph, determine;
          1. The maximum temperature charge. (1mk)
          2. The volume of solution A required to give the maximum change in temperature. (1mk)
        3. Calculate;
          1. Moles of sulphuric acid required to give maximum charge in temperature. (1mk)
          2. Molar enthalpy of reaction between sulphuric acid and solution C. Assume C = 4.2Jg-1K-1 density of solution 1g/cm3. (1mk)
  2. You are provided with solid D. Carry out tests below and write your observations and inferences in spaces provided.
    1. Describe the appearance of solid D. (1mk)
    2. Place all solid D in clean dry test tube and heat it strongly until no further change occurs. Test any gas produced with both red and blue litmus paper. Allow the residue to cool and use it for test C below.
       Observations  Inferences
       (2mks)  (2mks)
    3. Add about 10cm3 of 2MHCl to the residue and shake for about 3 minutes. Keep the mixture for test (d)
       Observation  Inferences
        (1mk)   (1mk)
    4.                           
      1. Place about 2cm3 of the mixture in a test tube then add aqueous ammonia until excess.
         Observation   Inferences
         (1mk)  (1mk)
      2. To the rest of the mixture add all solid E provided and shake the mixture well then filter.
         Observation  Inferences
         (1mk)  (1mk)
      3. To the filtrate add three drops of hydrogen peroxide then excess drops of ammonia solution.
         Observation   Inferences
         (1mk)  (1mk)
  3. You are provided with solid F. Carry out tests below. Write your observations and inferences in the space provided.
    1. Place all solid F in a boiling tube, add about 8cm3 of distilled water and shake the mixture well. (Retain the mixture for test b)
       Observation   Inferences
       (1mk)  (1mk)
    2.                     
      1. To about 2cm3 of mixture, add acidified potassium chromate VI and warm the mixture.
         Observation   Inferences
         (1/2 mk)  (1/2 mk)
      2. To about 2cm3 of the mixture, add two drops of acidified potassium manganate VII.
         Observation  Inferences
         (1mk)  (1mk)
      3. To the last portion, add universal indicator provided and match with pH chart.
         Observation  Inferences
         (1/2 mk)  (1/2 mk)

CONFIDENTIAL

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

  1. About 120cm3 solution A.
  2. About 120cm3 solution B.
  3. About 100cm3 solution C.
  4. About 0.5g of solid D in a stoppered and container.
  5. About 0.2g of solid E
  6. About 0.5g of solid F.
  7. One pipette
  8. One 250cm3 volumetric flask.
  9. One burette
  10. Two conical flasks
  11. 8 clean dry test tubes.
  12. Test tube rock.
  13. Thermometer.
  14. Two boiling tubes.
  15. Filter paper.
  16. One blue and one red litmus paper.
  17. One 10ml measuring cylinder.
  18. About 500ml distilled water in wash bottle.
  19. Test tube holder
  20. One pH chart range 1 – 4 and unwashed indicator paper.
  21. Spatula
  22. Two pieces of label.
  23. 10cm3 of 2MHCl.
    ACCESS
  24. Methyl orange with a dropper
  25. Bunsen burner
  26. 2MNH3(aq) with dropper.
  27. Acidified potassium dichromate (25g of K2Cr2O7 in 200 of 2MH2SO4 then top it to 1litre)
  28. Acidified potassium manganate VII (3.2g of KM2O4 in 200cm3 of 2MH2SO4 then top it to 1 litre)
    1. Solution A prepared by dissolving 50cm3 of 1.84g/cm3(98%). Conc sulphuric (VI) acid in about 600cm3 of distilled under the dropping it up to 1l.
    2. Solution B prepared by dissolving 8g of Na2CO3 in distilled water and topping it to 1 litre.
    3. Solution C prepared by dissolving 60g of NaOH to about 700cm3 of distilled water, top it up to 1 litre.
    4. Solid D is copper (II) carbonate
    5. Solid E is iron powder.
    6. Solid F malleic acid.

MARKING SCHEME

  1.                            
    1. Table I
      Completer table√
      (CT)
      Decimal √
      (D)
      Principal of averaging
      (PA)√
      Accuracy ± 001√
      (A) ± 0.2√
      Final accuracy
      FA                     
      5 .                
      1. School value
        = 21.6 cm3
      2. R.F.M of Na2CO3 = 23 x 2 + 12 + 16 x 3 = 106√ ½
        Molarity in mol/l = 8g√ ½
                                   106
        = 0.0754M √
      3. Moles of Na2CO3 used = 0.07547 x 25 =0.001887 moles
                                                       1000
        Moles of B: Solution A1
        1:1 moles of A1 = 0.001887 moles
        Molarity solution A1 = 0.001887 x 1000 =0.08736
                                                    21.6
      4. M1V1 = M2V2
        M1 = M2V2 = 0.08736 X 250
        25
        = 0.8736M
    2.                          
      1. Table II
         Test tube number   1  2  3  4  5  6
         Volume of solution A cm3  2  4  6  8  10  12
         Volume of solution C cm3  14  12  10  8  6  4
         Initial temperature of solution C (ºC)  20.5  20.5  20.5  20.5  20.5  20.5
         Highest temperature of mixture (ºC)  22.0  24.0  25.5  26.5  27.0  25.5
         Temperature charge ΔT (ºC)  1.5  3.5  5.0  6.0  6.5  5.0
        (6mks)
        CT = Award ½ mark for each practical done. (3mks)
        D = Decimal tied to fourth row 0.05.-√ (1mk)
        A = Accuracy: Temperature first ± 0.2 √ (1mk)
        Tr = Trend continuous rise, oriental then dye (1mk)
        graph adada
      2. Correct values ΔT from extrapolated graph.
        √ 1mk =7ºC
      3. Extrapolated graph show correct
        volume = 1mk√
        = 8.7cm3
      4.                      
        1.  Ans in (b) x ans in (iv)
                         1000
          = 8.7 x 0.8736 = 0.007576
                  1000
        2. Molar heat = MCΔT
          ans in (iii) x 1000
          = 16 x 4.2 x 7
          0.007576 x 1000
          = 62.0908 kJ/mol
          N/B 16 is total volume of A & C ie 8.7 + 7.3 = 16
2. a) Green powdery solid √
b.

Green solid changes black

Colourless liquid on cooler parts of the test tube

Blue litmus changes to red, red litmus changes remains red

Each observation ½ mark

Hydrated solid/ compound contains powder of crystallization

CO32- present

Each ½ mark

c.  Black solid dissolved forming a green solution Black is basic Fe2+ or Cu 2+ present each ½ mark.
d. i) Blue precipitate dissolves in excess forming deep blue solution. Cu2+ present
d) ii)  Effervescence occurred
- Brown residue
- Green filtrate

E above Cu2+ in reactivity series //

E displaces Cu2+

d. iii)

Green solution changes to yellow// brown

Brown precipitate formed

Fe2+ oxidized to Fe3
3. a)

Solid dissolved forming colourless solution.√ ½ mk

Polar substance // polar organic compound √ ½ mk

 
b. i) Orange colour of potassium chromate VI persists √ ½ mk

R-OH absent√  ½ mk

ii). Purple potassium manganate VII changes to colourless√ present
iii) PH3 Strongly acidic solution√

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