Chemistry Paper 3 Questions and Answers - Maranda Pre-Mock Examinations 2022

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QUESTIONS

  1.    
    1. You are provided with:     
      • Solution A - Acidified aqueous potassium manganate(VII).
      • Solution B - containing 23.5g of ammonium Iron (II) sulphate; (NH4)2Fe(SO4)2.6H20), per litre.
        You are required to Standardize the potassium manganate (VII), solution A, using the ammonium iron(II) sulphate, Solution B.
        Procedure
      • Fill the burette with solution A.
      • Pipette 25.0cm of solution B into a conical flask. Titrate solution B with solution until a permanent PINK colour just appears.
      • Record your results in table I below.
      • Repeat the titration two more times and complete the table below.
        Titre  1 2 3
        Final burette reading (cm3)      
        Initial burette reading (cm3      
        Volume of Solution A used (cm3      
        (4 marks)
        1. Determine the average volume of solution A used.
        2. Calculate the concentration of the ammonium iron (II) sulphate, Solution B, i moles per litre. (RFM of (NH4)2Fe(SO4)2.6H20) = 392) (1 mark)
        3. Calculate the number of moles of iron(II) ions in the 25.0cm of solution B. (1 mark)
        4. Using the ionic equation for the reaction between manganate(VII) ions iron(II) ions given below, calculate the concentration of manganate(VII) ions solution A in moles per litre.
          MnO4(aq) + 5Fe2+(aq) + 8H(aq)→Mn(aq) + 5Fe3+(aq) + 4H2O(I)
    2. You are provided with:
      1. 4.5g of solid D, Potassium chlorate in a boiling tube.
      2. Distilled water in a wash bottle
        You are required to determine the solubility of solid D at different temperatures
        Procedure
        1. Clean the burette and fill it with distilled water. 
        2. Place 5.0cm of distilled into the boiling tube containing solid D. 
        3. Warm the mixture until all the solid D dissolves. 
        4. Place the thermometer into the solution and remove it from the Bunsen burner flame. 
        5. Stir the solution with the thermometer gently as it cools. Note the temperature at which the crystals first appear and record it in table 2 below. 
        6. Add 5.0cm3 of distilled water into the mixture and repeat the procedure (c) -(e) above to complete table 2 below.
          Volume of water added(cm3) Temperature at which first crystals appear (C) Mass of KCIO3 in g/100g of water
          4    
          6    
             
          10     
          (6 marks)
        7. Plot a graph of solubility of KCIO3(y-axis) against temperature at which crystals first appear. (3marks)
      3. State the effect of changes in temperature on the solubility of KCIO3
      4. From your graph, determine the solubility of KClO3 at 55°C. n(1 mark)
  2. You are provided with solid R. Carry out the tests below. Write your observations and inferences in the spaces provided.
    1. Place about one third of solid R in a clean dry test-tube and heat it strongly.
      Observations Inferences
         
    2. Place the remaining solid R in a boiling tube. Add about 10cm of distilled water and shake well. Retain the mixture for tests in (d) below.
      Observations Inferences
         
    3. Use about 2cm3 portions of the mixture obtained in (c) for tests (i) to (iii) below.
      1. Add two to three drops of aqueous barium nitrate to the mixture.
        Observations Inferences
           
      2. Add five drops of dilute nitric(V) acid to the mixture. 
        Observations Inferences
           
      3. Add to the mixture, aqueous ammonia dropwise until in excess
        Observations Inferences
           
  3. You are provided with an IMPURE organic substance, solid Q. You are required to carry out the tests indicated below. Place a ALL of solid Q in a boiling tube. Add about 10 cm of distilled water and shake well. Divide the mixture into four equal portions in test tubes.
    Observations Inferences
       
    1. To the first portion, add two drops of acidified potassium manganate (VII) solution 
      Observations Inferences
         
    2. To the second portion, add three drops of acidified potassium dichromate(VI).
      Observations Inferences
         
    3. To the third portion, add all the sodium hydrogen carbonate.
      Observations Inferences
         
    4. Test the pH of the fourth portion using universal indicator solution provided.
      Observations Inferences
         

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

  1. Each candidate
    1. One burette 0 – 50 ml
    2. One pipette 25.0 ml and a pipette filler
    3. One Filter funnel
    4. Thermometer (-10ºC – 110ºC)
    5. Two clean and dry 250ml conical flasks
    6. Six clean and dry test-tubes
    7. One boiling tube
    8. 4.5g g of solid D weighed accurately and supplied in a dry stoppered container
    9. About 500cm3 of distilled water supplied in a wash bottle
    10. One 10ml measuring cylinder
    11. One metallic spatula
    12. About 150cm3 of solution A
    13. About 100cmof solution B
    14. pH chart
    15. About 0.5g of Solid R
    16. About 0.5g of solid Q
    17. About 0.2g sodium hydrogen carbonate
    18. A White tile
    19. Test tube holder
  2. Access to:
    1. Bunsen burner
    2. 2M nitric(V) acid supplied with a dropper
    3. 0.5M Barium nitrate supplied with a dropper
    4. 2M aqueous ammonia supplied with a dropper
    5. Universal indicator solution supplied with a dropper
    6. Acidified potassium manganate (VII) supplied with a dropper
    7. Acidified potassium dichromate (VI) supplied with a dropper

Note:

  1. Solid D is Potassium chlorate
  2. Solid R is Zinc sulphate
  3. Solid Q is Impure Maleic acid
  4. Solution A is prepared by dissolving 3.16g of potassium manganate(VII) in 400cm3 of 2M sulphuric(VI) acid and making it up to one litre of solution with distilled water.
  5. Solution B is prepared by dissolving 23.5g of hydrated ammoniuma Iron (II) sulphate, (NH4)2Fe(SO4)2.6H2O) per litre.
  6. Acidified potassium dichromate(VI) is prepared by dissolving 30g of potassium dichromate(VI) in 200cm3 of 2M sulphuric(VI) acid and diluting with distilled water to 1 litre.
  7. Acidified potassium manganate(VII) is prepared by dissolving 3.0g of solid potassium manganate (VII) in 200cm3 of 2M sulphuric(VI) acid and diluting with distilled water to 1 litre.


MARKING SCHEME

  1.    
    1.      
      1. titre 1 + titre 2 + titre 3 
                     3
        = average titre
      2. 23.5/392
        =0.05995moles per litre
      3. 25 x answer(b)
              1000
        = 0.001499
      4. moles of A used 
        = 1/5 x answer
        = Answer Q
        Moles of A in 1000cm3
        = answerQ x 1000
             average titre
        = correct answer
        M1V1 = 5
        M2V2
        M2 = answer(b) x 25
                5 x average titre
        = correct answer
    2.    
      1.   
        Volume of water added(cm3) Temperature at which first crystals appear(ºC) Mass KClO3 in g/100g of water
        8 75 56.25
        10 42 45.0
        12 30 37.50
        14 28 32.14
      2.      
        1
      3. increase in temperature increases the solubility of KClO3 / decrease in the temperature decreases the solubility of KClO3
      4. Showing
        correct reading
Observations Inferences

2a) colourless liquid forms on the cooler parts of the test tube residues yellow when hot and white when cold
b)Solid R dissolves to form a colourless solution
c, i) white precipitate
ii) white ppt, insoluble on addition of nitric(v) acid
iii)white ppt soluble in excess

3 dissolve to form a colourless solution
a) purple H+/ KMnO4(aq) changes to colourless
b) Orange H+/ K2Cr2O7(aq) changes to green
c) bubbles of a colourless gas/effervescence
d) PH = 3accept PH = 1,2,3







2a) water of crystallization or hydrated salt
ZnO
b) Soluble salt
Absence of colourless ions. Fe2+, Fe3+, Cu2+
c I) SO2-4, CO2-3, SO2-3 present
All 3 mentioned - 1mk
2 mentioned - mk
1 mentioned - 0mk
ii) SO2-4present
accept for mk
SO2-3, CO2-3 absent
iii) Zn2+

3) polar organic compound
a)
b) R-OH present
c) H+, H3O+, R-COOH
d) Strongly acidic


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