Chemistry Paper 3 Questions - Kapsabet Boys Post Mock 2023 Exams

INSTRUCTIONS 

•  Answer ALL the questions in the spaces provided in the question paper. You are NOT allowed to start working with the apparatus for the first 15 minutes of the 2¼ hours allowed for this paper. This time is to enable you to read the question paper and make sure you have all the chemicals and apparatus required.
• ALL working MUST be clearly shown where necessary
• Mathematical tables and electronic calculators may be used.

QUESTIONS

1. You are provided with:-
   • Solution H; which is 0.02M Potassium Manganate (VII) which is acidified.
   • Solution G; which is a mixture of Sodium Oxalate, Na₂C₂O₄ and oxalic acid, H₂C₂O₄
     You are required to:-
     1. Determine the solubility of Sodium Oxalate at room temperature.
     2. Determine the effect of temperature on the rate of reaction of Potassium Manganate (VII) and oxalic acid.
        Procedure I
        1.  Pipette 25.0cm³ of solution H into a clean conical flask. Heat the contents to about 70⁰c.
        2. Titrate the hot solution against solution G to a colourless end point.
           Record your results in table I
        3. Repeat steps (i) and (ii) two more times to obtain consistent titres.
           Keep the remaining solution G and H for procedure II
           Table I
           

           	I	II	III
           Final burette reading (cm3)
           Initial burette reading (cm3)
           Volume of solution G used (cm3)

           
           
           1.  Work out the average volume of solution G used. (1 mark)
           2.  
              1. Calculate the number of moles of potassium manganate (vii) in 25.0 cm³ of solution H. (1 mark)
              2. Given the following reactions:-
                 Na₂C₂O_4(aq) 2Na+ (aq) + C₂O _{42- (aq)}
                 C₂O _42-(aq) + 2H+(aq) H₂C₂O_4(aq)
                 2KMnO_4(aq) + 5H₂C₂O_4(aq)+ 3H₂SO_4(aq) K₂SO_4(aq) + 2MnSO_4(aq) + 8H2O(l) + 10CO_2(g)
                 1. Calculate the number of moles of oxalic acid that reacted with Potassium Manganate (VII) (1 mark)
                 2. Determine the mass of oxalic acid in the average volume used.
                    (H₂C₂O₄. 2H₂O) (H= 1.0, C= 12.0, O = 16.0) (1 mark)
           3. Given that solution G was prepared by dissolving 7.68 g of the mixture of oxalic acid and sodium oxalate in 1000cm³ of a solution.
              1.  Using your answer in b (ii) II work out the mass of oxalic acid in 1000 cm³ of solution G. (1 mark)
              2. From your answer above, calculate the mass of sodium oxalate in 1000 cm³ of the mixture. (1 mark)
              3. Hence calculate the solubility of sodium oxalate in g/100g of water. (2 marks
                 Procedure II
                 1. Using a measuring cylinder, transfer 5.0 cm³ of solution H into a clean boiling tube.
                 2. Using the burette measure 5 cm³ of oxalic acid, solution G into five test tubes labelled 1 – 5
                 3. Heat solution H until it reaches 80⁰C.
                 4. To the hot solution in (iii) add 5.0 cm³ of solution G from test tube 1 and start the stop watch at the same time. Stir the mixture using the thermometer and record time taken for the purple colour to disappear.
                 5. Repeat procedure (i) – (iv) at the temperatures shown using contents of test tubes 2, 3, 4 and 5 respectively.
                    Table II
                    

                    Temperature before mixing 00c	80	70	60	50	40
                    Time taken for purple colour to disappear in (sec)
                    1⁄????(sec-1)

           4. On the grid provided, plot a graph of 1/ t (y – axis) against temperature at which the purple colour disappear. (3marks)
           5. What does 1⁄? represent in this experiment. (1 mark)
           6. From the graph:
              1. Determine the time taken for the purple colour to disappear at 47.5⁰C. (1mark)
              2. How does temperature change affect 1⁄? in this experiment? Explain. (1 mark)
2. You are provided with 10 cm³ of solution J, which contains two cations and one anion. Carry out the tests below and record your observations and inferences in the spaces provided.
   1. Add 20 cm³of 2M aqueous sodium hydroxide to all of solution P provided. Shake well and filter the mixture into conical flask. Retain both the residue and filtrate.
      

      Obsevations	Inferences
      (1 mark)	(1 mark)

      
      
      
   2.  
      1. To about 2cm³ of the filtrate, add 2M Nitric acid drop wise until in excess.
         (i.e. about 1cm³ of the acid).. Retain the mixture.
         

         Observations		Inferences
         (1 mark)		(1mark)

         
         Divide the mixture in b (i) above into two portions.
      2. To the first portion, add aqueous sodium hydroxide drop wise until in excess.
         

         Observations		Inferences
         (1 mark)		(1mark)

      3. To the second portion, add aqueous ammonia drop wise until in excess.
         

         Observations		Inferences
         (1 mark)		(1mark)

   3. To 2 cm³ of the filtrate, add 3 drops of Potassium iodide
      

      Observations		Inferences
      (1 mark)		(1mark)

   4. To 2 cm³ of the filtrate, add 3 drops of acidified Barium nitrate solutions.
      

      Observations		Inferences
      1 mark)		(1mark)

   5. To the residue in (a), add 8 cm³ of dilute nitric acid and allow it to filter into a boiling tube.
      

      Observations		Inferences
      1 mark)		(1mark)

      
      
      1. To 2 cm³ of this filtrate, add aqueous ammonia drop wise until in excess.
         

         Observations		Inferences
         (1 mark)		(1mark)

3. You are provided with solid K. Place all the solid K in the boiling tube. Add 10 cm³ of distilled water and shake well. Divide the resulting mixture into four portions.
   

   Observations		Inferences
   (1 mark)		(1 mark)

   
   
   1. To the first portion add 2 drops of universal indicator. Compare the result with the PH chart.
      

      Observations		Inferences
      (1 mark)		(1mark)

   2. To the second portion add two drops of Bromine water.
      

      Observations		Inferences
      1 mark)		(1mark)

   3. To the third portion add drops of acidified potassium manganate (VII) solution H.
      

      Observations		Inferences
      (1 mark)		(1 mark)

   4. To the fourth portion add, a little amount of NaHCO_³
      

      Observations		Inferences
      (1 mark)		(1mark)