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

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.
           MnO_4(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
            8
            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 100cm³ of 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.      
         
      3. increase in temperature increases the solubility of KClO₃ / decrease in the temperature decreases the solubility of KClO₃
      4. Showing
         correct reading