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CHEMISTRY PAPER 3 - 2019 KCSE Prediction Questions Set 1

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  1. You are provided with:
    • Solution A, Dilute hydrochloric acid.
    • Solution B, made by dissolving 0.5g of sodium hydroxide in water and made to 250cm3 of solution.
    • Solid C, Magnesium ribbon.
    • Phenolphthalein indicator.

    You are required to:
    1. Standardize solution A.
    2. Determine the rate of reaction between solution A and magnesium.

    PROCEDURE I:
    1. Measure exactly 1 Ocm3 of solution A using a burette and transfer into a 250ml volumetric flask. Top up to the mark using distilled water and shake thoroughly. Label this solution D.
    2. Drain the remaining solution A in the burette, rinse the burette thoroughly and fill the burette with solution D.
    3. Pipette 25cm3 of solution B into a conical flask. Add three drops of phenolphthalein indicator.
    4. Titrate solution D with solution B. Record your results in the table below. Repeat procedures (i) to (iv) to complete the table. 
         1  2  3
      Final burette reading (cm3)       
       Initial burette reading (cm3)      
       Volume of solution D used (cm3)      
      (3 marks)
      1. Calculate the average volume of solution D used.(show your working) (1 mark)
      2. Write an equation for the reaction that took place. (1 mark)
      3. Calculate the molarity of sodium hydroxide solution.(Na =23,0=16,H=l ) (1 mark)
      4. Calculate the number of moles of sodium hydroxide reacted. (1 mark)
      5. Calculate the number of moles of hydrochloric acid in 250cm3 of solution D. (2marks).
      6. Calculate the m9larity of hydrochloric acid in solution A. (1 mark)

    PROCEDURE II:
    1. Cut solid C into equal pieces, each 2cm long.(I mark)
    2. Using a burette, measure 12cm3 of solution A, into a clean boiling tube.
    3. Drop one piece of solid C into the boiling tube containing solution A and start the stopwatch immediately. Stop the stopwatch when all solid C has just disappeared (dissolved).
      Record your results in the table below.
    4. Repeat steps (ii) and (iii) above using 10.0cm3, 8.0cm3, 6.0cm3 and 4.0cm3 of solution A. Top up each with distilled water to make12.0cm3 of solution, using a 10.0cm3 measuring cylinder and complete the table below. (4marks)
         Volume of Solution A (cm3)  Volume of distilled water (cm3)   Concentration of Solution A (moles/dm3)   Time (s)   I/t (S-1)
       I   12  0      
       II  10  2      
       III  8  4      
       IV  6  6      
       V  4  8      
      (4 marks)
      1. Calculate the concentration of each of the solution and and complete the table. Show your working. (2marks)
      2. Plot a graph of I/t (y-axis) against the concentration of solution A. (3marks)
      3. From the graph, determine the time taken for the reaction to reach completion when 1.5 moles of solution A are used. (2 marks)
      4. Comment on the shape of the graph. (1 mark)
  2. You have been provided with solid Q, Which is a mixture of two compounds.
    You are required to carry out the test below and record your observations and inferences in the spaces provided below.

    PROCEDURE
    1. Put a spatulaful of mixture Q in a boiling tube.
    2. Add about 7cm3 of distilled water to the mixture and shake thoroughly. Filter the mixture.
    3. Wash the residue with distilled water and keep both the residue and the filtrate.
       Observation  Inference
                1 mark       1 mark
    4. Divide the filtrate into four portions
       Observation  Inference
                1 mark       1 mark
    5. Add 5 drops of acidified 2M barium chloride to the first portion.
       Observation  Inference
                1 mark       1 mark
    6. Add 3 drops of 2M lead (II) nitrate solution to the second portion.
       Observation  Inference
                1 mark       1 mark
    7. Add 2M sodium hydroxide to the third portion dropwise until in excess.
       Observation  Inference
                1 mark       1 mark
    8. Add 2M ammonia solution to the fourth portion drop wise until in excess.
       Observation  Inference
                1 mark       1 mark
    9.  Scrape the residue from the filter paper and transfer it into a boiling tube.
    10. Add some dilute 2M Nitric (V) acid while shaking until all the solid dissolves.
    11. Divide the solution into three portions.
    12. To the first portion add 2M sodium hydroxide a few drops till in excess.
       Observation  Inference
                1 mark       1 mark
    13.  To the second portion add a few drops of 2M ammonia solution till in excess.
       Observation  Inference
                1 mark       1 mark
    14. To the third portion add 5 drops of 2M hydrochloric acid and warm the mixture.
       Observation  Inference
                1 mark       1 mark
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Read 12249 times Last modified on Thursday, 06 June 2019 13:01

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