Chemistry Paper 3 Questions and Answers with Confidential - Kapsabet Mock Exams 2021/2022

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INSTRUCTIONS TO CANDIDATES

  1. Answer ALL questions in the spaces provided in each question.
  2. Mathematical tables and electronic calculators may be used for calculations.
  3. all working must be clearly shown where necessary.

 

  1. You are provided with
    • 2.0M NaoH solution labelled B
    • Sulphuric(VI) acid solution labelled A `
      You are to:
      1. Prepare a dilute solution of NaoH solution.
      2. Determine the concentration of in moles per litre.
        PROCEDURE 1
        1. Using a pipette 25.0cm3 of solution B and place it into 250cm3 volumetric flask.
        2. Add about 200cm3 of distilled water and share well.
        3. Add more water to make up to 250cmmark. Label this solution C
          1. Calculate the concentration of the dilute solution C in moles per litres. [2mks]
            PROCEDURE 2
            1. Fill the burette with solution A and record the readings in the table below.
            2. Pipette 25cm3 of dilute solution C and place it into 250ml conical flask.
            3. Add 2-3 drops of phenolphthalein indicator.
            4. Titrate with solution A.
            5. Record your results in the table below.
            6. Repeat the titration two or more times and complete the table.
                II III
              Final burette reading (cm3)      
              Initial burette reading(cm3)      
              Volume of solution A(cm3)      
              [4mks]
              1. Determine average volume of the acid (solution A) used. [1mk]
              2. Determine moles of dilute solution C in the volume used. [2mks]
              3. Write an equation for the reaction taking place. [1mk]
              4. Determine the number of moles of A used. [2mks]
              5. Determine the concentration of A in moles per litre. [2mks]
  2. You are provided with the following
    • 2M sodium hydroxide solution, solution B
    • 2M hydrochloric acid, solution D
      You are required to determine the molar enthalpy of neutralization of the acid using sodium hydroxide.
      PROCEDURE
      1. Measure out 20cm3 of acid into a clean plastic beaker.
      2. Record the temperature of this solution in the table below
      3. Measure 5cm3 of sodium hydroxide and add it to the hydrochloric acid.
      4. Stir with the thermometer and record the maximum temperature reached.
      5. Repeat the above procedure adding 5cm3 portions of sodium hydroxide until the total volume of the solution is 50cm3.
        Volume of acid(cm3) 20 20 20 20 20 20 20
        Volume of NaoH added cm3 0 5 10 15 20 25 30
        Temperature(°C)of solution               
        [3mks]
        You are required to:
        1. Plot a graph of temperature rise against sodium hydroxide added. [3mks]
          1
        2. From your graph determine:
          1. maximum temperature change. [1mk]
          2. the volume of NaOH that is required for complete neutralization [1mk]
          3. Calculate the molar enthalpy of neutralization for this reaction. (C=4.2J/g/K) assume density of solution is 1gcm-3) [2mks]
          4. The theoretical molar heat of neutralization is -57.2kj/mol-1.Compare your value in [ii] above with the theoretical value. Give the reasons for any differences noted between these two values. [2mks]
  3. You are provided with solid N carry out the tests below and record your observations and inferences.
    1. Place a spatula of N in a test tube and add 5cm3 of water and shake well divide the solution in to three portions.
      OBSERVATION (2mks) INFERENCE (1mk)
         
    2. Add sodium hydroxide to the first portion drop wise while observing till in excess
      OBSERVATION (2mks) INFERENCE (1mk)
         
    3. Add ammonia solution to the second portion drop wise until in excess.
      OBSERVATION (2mks) INFERENCE (1mk)
         
    4. Add four drops of potassium iodide solution to the third portion.
      OBSERVATION (2mks) INFERENCE (1mk)
         
    5. Add three drops of acid barium nitrate to the fourth followed by 5 drops of nitric acid.
      OBSERVATION (2mks) INFERENCE (1mk)
         

CONFIDENTIAL

  • Burette
  • Pipette
  • 2 conical flasks
  • 120cmof 2.0M NaoH labelled B
  • 100cm3 0f 0.2M H2SO4 labelledA
  • 250cm3 volumetric flask
  • A label
  • Pipette filter
  • Stand and clamp
  • 500cm3 distilled water
  • Phenolphthalein indicator
  • 100cm3 plastic beaker
  • Thermometer
  • 10cm3 measuring cylinder
  • 100cm3 measuring cylinder
  • 50cm3 2.0M HCl , Solution D
  • 50cm3 2.0M NaoH
  • 6 test tubes in a test tube rack
  • 0.2g of solid N (Al2(SO4)3]

REAGENTS

  • 2M NaoH
  • 2M NH4OH
  • Ba (NO3) 2solution
  • 2M nitric acid
  • Potassium iodide solution


MARKING SCHEME 

PROCEDURE 1

  1. 2 moles →1000cm25 × 1 =0.05 moles
                                      1000
    ? 25cm3
    0.05 moles-250cm0.05×1000 =0.2m
                                          250
    PROCEDURE II
    Complete table 1
    Decimal 1
    Arithmetic 1
    Accuracy 1=0.2
    1. 12.5+12.5+12.5=12.5cm
                  3
    2. 0.2 moles→1000cm0.2m × 25=0005 moles
                                           1000
      25cm3
    3. 2NaoH [aq]+H2SO4[aq]→NaSO4[aq]+2H2O[l]
    4. Mole ratio
      A:C C=0.0025moles
      1:2 A=0.005=0.0025 moles
                    2
    5. 0.0025→answer a=0.0025×1000
                                        answer a
      1000
  2. Table
    Complete table 1
    Decimal point 1
    Trend 1 
    1. Graph
      2
      Axis -½Mk each
      Scale-½Mk each
      Plotting 1 mk
      Curve 1 mk
    2.    
      1. answer from the graph
      2. Use MCDθ
        Mass=50×1=50g.
        From MCDθ→50g×4.2/g J/g/°C × answer in b [i] above.
      3. Theoretical value is higher than the obtained value
        Heat lost to the surrounding[1mk]
        Heat absorbed by the apparatus[1mk]
  3.    
    1.    
      Observation Inference
      It dissolves into[½]a colourless solution[½mk] Soluble salt[½]NoCu2+,Fe2+ or Fe3+[½ mk]
    2.    
      Observation Inference
      White precipitate soluble in excess [1mk] Pb2+,Zn2+,Al3+ ions present[ 2mks] for the 3 
    3.    
      Observation Inference
      White precipitate insoluble in excess[1mk]  Pb2+,Al3+ ions present[1mk]
    4.     
      Observation Inference
      No Yellow precipitate formed[1mk] Pb2+ ions absent/ Al3+ present[1mk]

    5. Observation Inference
      White precipitate [1mk]
      Don’t dissolve on adding nitric acid
      SO42-ions[1mk]

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