Chemistry Paper 3 Questions with Confidentials - Mokasa II Mock Examination 2021/2022

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Chemistry
PAPER 3
PRACTICAL

INSTRUCTIONS TO CANDIDATES

  • 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 21/4 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:
    1. Solution B, containing 2MHCl
    2. Solid A, Magnesium ribbon
    3. Solution D, containing 0.2M NaOH
    4. Solution X, containing 0.15M Sodium thiosulphate
      • You are required to: determine
        1. Molar heat of reaction between Magnesium and Hydrochloric acid
        2. Rate of reaction between Hydrochloric and Sodium thiosulphate
      • PROCEDURE I
        1. Place 20cm3 of solution B into 50ml plastic beaker and measure the initial temperature of solution B
          Initial temperature of solution B OC (1/2mk)
        2. Add all the Solid A provided to solution B and stir the mixture with a thermometer, measure the maximum temperature of solution.
          Maximum temperature of the solution OC (1/2mk)
        3. Transfer the resulting solution formed into a 250ml volumetric flask, add distilled water upto the mark, shake the mixture well and label it as solution C
        4. Fill the burette with solution C upto 0.0mark, pipette 25cm3 of solution D into a clean conical flask and add 2-3 drops of phenolphthalein indicator.
        5. Titrate the two solutions until the pink colour turns colourless. Repeat the titration two more times and record the values in table I below
      •          
        1. Table I (4mks)
            I II III
          Final burette reading                               
          Initial burette reading      
          Volume of C used (cm3)      
        2. Calculate the average volume of solution C used (1mk)
        3. Calculate the number of moles of NaOH, Solution D used (1mk)
        4. Calculate the number of moles of Hydrochloric acid:
          1. In the average volume of solution C used (1mk)
          2. In 250cm3 of solution C (1mk)
          3. In original, 20cm3 of solution B (1mk)
          4. That reacted with solid A, Magnesium (1mk)
        5. Determine the molar heat of reaction between Hydrochloric acid, solution B and solid A, Magnesium (4.2Jg-1K-1, Density =1g/cm3) (2mks)
      • PROCEDURE II
        1. Measure 30cm3 of solution X and transfer into a clean conical flask
        2. Place the conical flask containing solution to a white piece of paper marked X
        3. Add 10cm3 of solution B to the content of the conical flask swirl the flask and immediately start a stop watch, record the time taken for the mark X, to be invisible from above. Record the value in the table II below.
        4. Repeat the procedure (iii) above using the volumes of solution X and distilled water indicated in table II below
      •                
        1. Table II (6mks)
          Experiment  Volume of
          solution X (cm3)
          Volume of
          water (cm3)
          Time
          (seconds)
          1/Time
          ( Sec-1)
          30  0    
          2 25 5    
          3 20 10    
          4 15 15    
          5 10 20    
          NB: Calculate the values Rate, 1/Time to 3 decimals and record in table II above
        2. Plot a graph of rate, 1/Time (sec-1) against volume of solution X (Horizontal axis) (3mks)
        3. From the graph, determine the time taken for mark X to be invisible when 18cm3 of water is used (1mk)
  2. You are provided with solid K, which is a mixture of two salts, carry out the following tests on solid K and record observations and inferences in the spaces provided
    Place all the solid K in a boiling tube and about 10cm3 of water and shake well, filter the content of the boiling tube into a clean test tube, keep the RESIDUE and FILTRATE for tests below.
    1.                     
      1. To about 2cm3 of filtrate and add about 2M Sodium hydroxide until in excess
        Observation                        Inference                             
           
      2. Dip glass rod into about 2cm3 of the filtrate and place it in a Non-luminous flame
        Observation                        Inference                             
           
      3. To about 2 cm3 of filtrate add about five drops of hydrochloric acid, followed by 3 drops of Barium Chloride solution
        Observation                        Inference                             
           
    2. Dry the residue between filter paper, Place half of it into a clean dry test tube and heat it strongly
      Observation                        Inference                             
         
    3.       
      1. Place the remaining residue into another clean test tube and about 5cm3 of dilute Nitric (v) acid, shake the mixture and test any gases produced using a burning splint. Use the solution formed for tests below.
        Observation                        Inference                             
           
      2. To about 1cm3 of the solution add 2M Sodium hydroxide drop wise until in excess.
        Observation                        Inference                             
           
      3. To about 2cm3 of solution add 3 drops of Potassium Iodide solution.
        Observation                        Inference                             
           
  3. You are provided with solution Z in a test tube , use it to carry the tests below and record observations and inferences in the spaces provided.
    Divide the solution into four portions.
    1. To the 1st portion, add 2cm3 of water and let the mixture to stand for a minute.
      Observation                        Inference                             
         
    2. To the 2nd portion, add all the sodium Hydrogen carbonate provided.
      Observation                        Inference                             
         
    3. To the 3rd portion, add 3 drops of acidified Potassium Manganate VII and warm.
      Observation                        Inference                             
         
    4.              
      1. Solution Z is suspected to be an Alkanoic acid, describe a test that can be carried out to confirm presence of alkanoic acid using Ethanol and any other necessary reagent and condition provided on the bench.
        Test                       Expected observation                             
           
      2. Carry out the test described in d(i) above.
        Observation                        Inference                             
           


Confidential

Each student will require: -

  1. 100cm3 of solution X
  2. 100cm3 of solution D
  3. 100cm3 of solution B
  4. 1g of solid K in stopped container
  5. 10cm3 of solution Z in a test tube
  6. 5cm3 of Ethanol in a test tube
  7. 3cm Mg ribbon (labeled solid A)
  8. 1 label
  9. 50ml Burette
  10. 25 ml pipette
  11. 2 conical flasks
  12. 50ml plastic beaker
  13. Thermometer
  14. 2 filter papers
  15. White tile
  16. Test tube rack with 6 test tubes
  17. Complete stand
  18. Test tube holder
  19. 250ml volumetric flask
  20. Stopwatch
  21. 0.5g of NaHCO3
  22. Wooden splint
  23. White piece of paper
  24. Distilled water in wash bottle
  25. Two boiling tubes
  26. 10ml measuring cylinder
  27. Glass rod

Access to:

  1. 2M NaOH with dropper
  2. Barium chloride solution with dropper
  3. Hydrochloric acid with dropper
  4. Nitric (V) acid with dropper
  5. Acidified potassium manganate VII with dropper
  6. Potassium iodide solution with dropper
  7. Concentrate sulphuric (VI) acid with dropper
  8. Source of heat

Identity of solutions and solids

  • Solution X : - 0.15M Sodium thiosulphate
  • Solution D : - 0.2M Sodium Hydroxide
  • Solution B : -2M Hydrochloric acid
  • Solution Z : - Acetic acid
  • Solid K :- Mixture of 0.5g PbCO3 and 0.5g Na2SO4

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