KCSE 2019 Chemistry Paper 3 Questions and Marking Schemes

Chemistry Paper 3 (233/3)

1. You are provided with:
   • Solution A: aqueous Iron(III) sulphate.
   • Solution B: aqueous potassium iodide.
   • Solution C: mixture of aqueous starch and sodium thiosulphate solution.
     
     You are required to determine the rate of reaction between aqueous Iron(III) sulphate (solution A) and aqueous potassium iodide (solution B).
   • Procedure:
     1. Place 5 test tubes on a test tube rack and label them 1, 2, 3, 4 and 5. Fill a burette with solution A. To each test tube place 3 cm³ of solution A from the burette.
     2. Clean the burette and fill it with solution B. Place 8 cm³ of solution B into a 100 ml beaker from the burette.
     3. Using a 10ml measuring cylinder, add 2cm³ of solution to the beaker containing solution B followed by 7 cm³ of distilled water measured using the same 10 ml measuring cylinder.
     4. Pour the contents of test tube 1 to the mixture in the beaker and immediately start the stop watch. Swirl the contents of the beaker. Record in table 1 the time taken for a blue colour to just appear. Measure the temperature of the final mixture and record in the space provided. Wash the beaker and proceed to step (v).
     5. Place 6cm³ of solution B into 100 ml beaker from the burette. Add 2cm³ of solution C followed by 9 cm³ of distilled water. Add solution A in test tube 2 to the mixture in the beaker and immediately start the stop watch. Swirl the contents of the beaker. Record in table 1 the time taken for a blue colour to just appear. This is experiment 2.
     6. Wash the beaker. Repeat step (v) with solution A in test tubes 3, 4 and 5 with corresponding volumes of solution B, solution C and distilled water as indicated in table 1 for experiments 3, 4 and 5.
        
        
        1. Temperature of final mixture  .....................°C(1 mark)
        2. Table 1
           

           Experiment	Volume (cm³) of				Time (seconds)
           	Solution A	Solution B	Solution C	Distilled Water
           1	3	8	2	7
           2	3	6	2	9
           3	3	5	2	10
           4	3	4	2	11
           5	3	3	2	12

           (3 marks)
        3. Complete table 2 for each experiment by:
           1. calculating the square of volume of solution B, BP and filling in the table.
           2. calculating the rate of reaction which is given by the expression
              Rate =¹/_time X 1000 s^-1 and filling in the table.
              Table 2
              

              Experiment	B2	Rate =1/time X 1000 s-1
              1
              2
              3
              4
              5

              (5 marks)
        4. Plot a graph of rate (y-axis) against B (3 marks)
        5. Using the graph, determine the time that it will take for the blue colour to appear if the experiment is repeated using the following mixture:
           

           Volume (cm³) of
           Solution A	Solution B	Solution C	Distilled water
           3	7	2	8

           (2 marks)
        6. In this experiment the rate of reaction was determined with respect to potassium iodide. Describe how the rate of the reaction can be determined with respect to Iron(III) sulphate. (2 marks)
2. You are provided with solid P. Carry out the following tests and record the observations and inferences in the spaces provided.
   1. Place about one-third of solid P in a dry test tube and heat it strongly. Test any gases produced with red litmus paper.
      

      Observations	Inferences
      (2 marks)	(1 mark)

   2. Place the remaining amount of solid P in a boiling tube. Add about 15cm of distilled water and shake to dissolve the solid. Use about 2 cm³ portions of the solution in a test tube for each of the tests (i) to (iv).
      1. To the first portion of the solution add aqueous sodium hydroxide.
         

         Observations	Inferences
         (1 mark)	(2 marks)

      2. To the second portion of the solution add 2 or 3 drops of aqueous barium nitrate.
         

         Observations	Inferences
         (1 mark)	(1 mark)

      3. To the third portion of the solution add 2 or 3 drops of aqueous lead(II) nitrate. Warm the mixture.
         

         Observations	Inferences
         (1 mark)	(1 mark)

      4. To solid D in the test tube add about 2 cm of distilled water. Shake and label this as chlorine water. Add all the chlorine water to the fourth portion of the solution. Shake the mixture and then add 3 drops of starch solution.
         

         Observations	Inferences
         (2 marks)	(1 mark)

   3. Give the formulae of the ions present in solid P:
      1. cation
      2. Anion
3. You are provided with liquid Q. Carry out the following tests and record the observations and inferences in the spaces provided.
   1. Place 2 drops of liquid Q on a watch glass. Ignite the liquid with a Bunsen bumer flame.
      

      Observations	Inferences
      (1 mark)	(1 mark)

   2. Place about 2 cm of liquid Q in a test tube. Add about 2 cm of distilled water and shake the mixture.
      

      Observations	Inferences
      (1 mark)	(1 mark)

   3. To about 2 cm of liquid Q in a test tube, add all of the solid sodium hydrogen carbonate provided
      

      Observations	Inferences
      (1 mark)	(1 mark)

   4. To about 2 cm of liquid Q in a test tube, add 2 or 3 drops of bromine water.
      

      Observations	Inferences
      (1 mark)	(1 mark)

   5. To about 2 cm3 of liquid Q in a test tube, add 2 or 3 drops of acidified potassium dichomate(VI) and warm the mixture.
      

      Observations	Inferences
      (1 mark)	(1 mark)

MARKING SCHEME

1.     
   1. Temperature of final mixture 22,5°C (1 mark)
   2. Table 1
      

      Experiment	Time (seconds)
      1	14.1
      2	22.0
      3	32.0
      4	49.0
      5	78.2

      (3 marks)
      Complete table (1½ mark)
      Decimal (½ mark)
      Accuracy (½ mark)
      Trend (½ mark)
      
      
   3. Table 2
      

      Experiment	B2	Rate =1/time X 1000 s-1
      1	64	70.9
      2	36	45.5
      3	25	31.3
      4	16	20.4
      5	9	12.8

      Note: All points lie on a straight line except for B=8, B² = 64, rate = 70.9S^-1
      Correctly worked B2.
      each value to a maximum of 2'/2 marks
      Correctly worked rate
      for each value to a maximum of 22 marks
      (5 marks)
   4.    
      
      Scale-1/2
      Labelled Axes - 1/2
      Line - 1
      Plots 1 
      (3 marks)
   5. B=7, B² -= 49
      From the graph, Rate = ¹⁰⁰⁰/_time = 62
       ∴time= ¹⁰⁰⁰/₆₂=16.1s
   6. Keep volume of solution B and solution C constant. Use different volumes of solution A Calculate appropriate volume of distilled water to use to make total volume constant. (2 marks)
2. You are provided with solid P. Carry out the following tests and record the observations and inferences in the spaces provided.
   1. Place about one-third of solid P in a dry test tube and heat it strongly. Test any gases produced with red litmus paper.
      

      Observations	Inferences
      -red litmus paper turns blue  - white fumes which form a white solid on the sides of the test tube. OR - the white solid sublimes.	an ammonium salt OR basic gas OR NH+₄ ions present.
      (2 marks)	(1 mark)

   2. Place the remaining amount of solid P in a boiling tube. Add about 15cm of distilled water and shake to dissolve the solid. Use about 2 cm³ portions of the solution in a test tube for each of the tests (i) to (iv).
      1. To the first portion of the solution add aqueous sodium hydroxide.
         

         Observations	Inferences
         No white precipitate	Inferences Zn2+ /Pb2+ Al3+/Mg2+ / Ca2+ ions absent
         (1 mark)	(2 marks)

      2. To the second portion of the solution add 2 or 3 drops of aqueous barium nitrate.
         

         Observations	Inferences
         No white precipitate	Inferences SO2-4/SO2-3/CO2-3 ions absent
         (1 mark)	(1 mark)

      3. To the third portion of the solution add 2 or 3 drops of aqueous lead(II) nitrate. Warm the mixture.
         

         Observations	Inferences
         White precipitate (V2 mark), which dissolves  on warming	Cl- or Br- ions present
         (1 mark)	(1 mark)

      4. To solid D in the test tube add about 2 cm of distilled water. Shake and label this as chlorine water. Add all the chlorine water to the fourth portion of the solution. Shake the mixture and then add 3 drops of starch solution.
         

         Observations	Inferences
         Colourless solution turns yellow (1 mark) Yellow colour persists OR no blue colour with starch.	Br- ions present I- ions absent
         (2 marks)	(1 mark)

   3. Give the formulae of the ions present in solid P:
      1. cation - NH⁺₄
      2. Anion - Br^-
3. You are provided with liquid Q. Carry out the following tests and record the observations and inferences in the spaces provided.
   1. Place 2 drops of liquid Q on a watch glass. Ignite the liquid with a Bunsen bumer flame.
      

      Observations	Inferences
      - Burns with a yellow flame	Long chain hydrocarbon or unsaturated compound
      (1 mark)	(1 mark)

   2. Place about 2 cm of liquid Q in a test tube. Add about 2 cm of distilled water and shake the mixture.
      

      Observations	Inferences
      Two layers formed OR Q not soluble/ immiscible in water	Non-polar compound
      (1 mark)	(1 mark)

   3. To about 2 cm of liquid Q in a test tube, add all of the solid sodium hydrogen carbonate provided
      

      Observations	Inferences
      No effervesence	Q is not acidic  OR Absence od carboxylic acid  OR RCOOH/H+/H3O+
      (1 mark)	(1 mark)

   4. To about 2 cm of liquid Q in a test tube, add 2 or 3 drops of bromine water.
      

      Observations	Inferences
      Bromine water not decolourised	Alkene/alkyne absent
      (1 mark)	(1 mark)

   5. To about 2 cm3 of liquid Q in a test tube, add 2 or 3 drops of acidified potassium dichomate(VI) and warm the mixture.
      

      Observations	Inferences
      Orange colour persists  OR No green colour formed	Alcohol absent OR R-OH absent
      (1 mark)	(1 mark)