Chemistry Paper 3, with Confidential - 2020 MOKASA JOINT MOCKS EXAMINATION (QUESTIONS AND ANSWERS)

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CHEMISTRY PAPER 3 CONFIDENTIAL

In addition to the common laboratory apparatus and fittings, each candidate shall be supplied with the following

  • 60 cm3of 0.5M copper (II) sulphate labeled solution K
  • 5g of Solid L
  • 90cm3 of acidified potassium manganate(VII), labelled as Solution M
  • 60 cm3of 2M sulphuric (VI) acid, H2SO4
  • 2ml of solution X
  • 2ml of solution Y
  • 2ml of solution Z
  • About 8 cm3of liquid E in a stoppered test tube
  • About 2g of solid Q in a stoppered container
  • Burette
  • Pipette and pipette filler
  • Three conical flasks
  • 10ml measuring cylinder.
  • 250 ml plastic beaker
  • 250 ml volumetric flask with a stopper
  • 1 label
  • Stop watch
  • Clean glass rod/looped nichrome wire
  • Clean and dry Metallic spatula
  • Thermometer (-10-1100c)
  • four test tubes
  • test tube holder
  • Filter paper
  • Filter funnel
  • Retort stand
  • white tile
  • 10ml measuring cylinder.
  • 50ml measuring cylinder.

 

Access to the following:

  • Distilled water
  • Bunsen burner
  • Acidified potassium dichromate (VI) supplied with a dropper.
  • 2M Barium nitrate solution supplied with a dropper.
  • 2M lead (II) nitrate supplied with a dropper
  • 2M Nitric (V) acid supplied with a dropper
  • Sodium hydrogen carbonate solid supplied with a spatula

 

Note

  • Solid Q is Na2SO3
  • Liquid E is ethanol
  • Solution K is prepared by accurately weighing 125g of hydrated copper (II) sulphate and making up to 1000 cm3 of solution
  • Solution M is prepared by accurately weighing 3.2g of KMnO4.then dissolving in 100ml of 2M sulphuric acid and topping up to 1000ml of the solution
  • Solution X is 2M potassium nitrate
  • Solution Y is made by dissolving One Spatulaful of blue Toss detergent in 100ml of distilled water (do not use tap water)then filter
  • Solution Z is 2M copper (II) sulphate solution

CHEMISTRY PAPER 3 CHEMISTRY PRACTICAL QUESTIONS

Question 1

You are provided with the following reagents:

  • Solution K- Copper (II) sulphate solution
  • Solid L- Iron powder
  • Solution M- Acidified Potassium Manganate (VII) solution, containing 0.8g of Potassium Manganate (VII) in 250cm3 of the solution.

You are required to determine the molar heat of displacement of copper in a solution of its ions by iron metal.

Procedure I

  • Place 50cm3 of Solution K in a 100cm3 plastic beaker using a burette.
  • Measure the constant temperature of the solution and record it in the Table 1 below.
  • Add all of the Solid L provided at once and start a stop watch immediately.
  • Using a thermometer, Stir the mixture thoroughly and continuously and record the temperature of the mixture after every one minute in the table 1.
  • Retain the resultant mixture for use in the next Procedure II.

Table 1

Time (Min) 0 1 2 3 4 5 6 7 8 9 10
Temperature(0C)                      

(3 marks)

  1. Plot a graph of temperature (vertical axis) against time on the grid provided below. (3 marks)
  2. From the graph you have drawn, determine the;
    1. highest change in temperature, ∆T (1 mark)
    2. time taken for the reaction to completely occur (1 mark)
  3. Calculate the heat change for the reaction. (Take density of the solution to be 1g/cm3 and specific heat capacity of the solution to be 4200kJ/Kg/K)  (2 marks)

Procedure II

  • Swirl the mixture obtained in procedure I above and filter into a 250mL volumetric flask.
  • Thoroughly rinse the beaker with 20cm3 of distilled water and ensure all the mixture has been transferred onto the filter paper.
  • Add 50cm3 of 2M Sulphuric (VI) acid to the filtrate mixture in the volumetric flask.
  • Add more distilled water to the solution in the volumetric flask to the mark. Mix the contents thoroughly and label this solution as Solution N.
  • Fill the burette with Solution M.
  • Place 25 cm3 of Solution N into a 250 cm3 conical flask using a pipette and a pipette filler.
  • Titrate Solution N against Solution M until the first permanent pink colour is seen.
  • Record your results in Table 2
  • Repeat the titration twice and complete Table 2.

Table 2

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

(3 marks)

  1. What is the average volume of Solution M used? (1 mark)
  2. Calculate the molarity of Solution M, KMnO4 (1 mark) (K=39, Mn=55, O=16)
  3. Calculate the number of moles of:
    1. Potassium manganate (VII) used, solution M   (1 mark)
    2. Iron (II) ions in 25cm3 of solution N      (1 mark)

      The equation for the reaction is:

      MnO4-(aq) + 8H+ (aq) + 5Fe2+ (aq)        ->         Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)
    3. Iron (II) ions in the 250cm3 of solution N (1 mark)
  4. Determine the molar heat of displacement of copper from a solution of its ions by iron metal (2 marks)
  5. Draw an energy level diagram for the reaction      (2 marks)

Question 2

  1. You have been provided with solutions X, Y and Z. Carry out the flame tests for each and indicate the colour of the flames and inferences below.(3 marks)

    Ions Flame Colour Inference
    X    
    Y    
    Z    
  2. You are provided with Solid Q. Carry out the tests below and Write your observations and inferences in the spaces provided.
    1. Place all Solid Q in a clean test tube. Add about 8cm3 of distilled water and shake. Divide the solution into 3 portions
      Observation Inference
      (1/2 mark)   (1/2 mark)
    2. To the first portion add a few drops of Lead (II) nitrate solution and warm
      Observation Inference
      (1 mark)   (1 mark)
    3. To the first portion add a few drops of Barium nitrate solution followed by few drops of dilute hydrochloric acid.

      Observation Inference
      (1 mark)   (1 mark)


    4. To the third portion add a few drops of acidified potassium dichromate (VI) then warm gently.

      Observation Inference
      (1 mark)   (1 mark)
  1. You have been provided with Liquid E.
    1. Place about 2cm3 of the Liquid E in a clean test tube. Add an equal amount of distilled water and shake the mixture. Allow to settle.

      Observation Inference
      (1 mark)   (1 mark)
    2. Place about 2cm3 of the Liquid E in a clean test tube. Add a half spatulaful of sodium hydrogen carbonate.
      Observation Inference
      (1 mark)   (1 mark)
    3. To about 2cm3 the Liquid E add 3 drops of acidified potassium dichromate (VI) solution and warm gently.
      Observation Inference
      (1 mark)   (1 mark)
    4. Take a few drops of Liquid E on a clean and dry metallic spatula and ignite over a non-luminous Bunsen flame.

      Observation Inference
      (1 mark)   (1 mark)


Marking Scheme

Question 1

You are provided with the following reagents:

  • Solution K- Copper (II) sulphate solution
  • Solid L- Iron powder
  • Solution M- Acidified Potassium Manganate (VII) solution, containing 0.8g of Potassium Manganate (VII) in 250cm3 of the solution.

You are required to determine the molar heat of displacement of copper in a solution of its ions by iron metal.

Procedure I

  • Place 50cm3 of Solution K in a 100cm3 plastic beaker using a burette.
  • Measure the constant temperature of the solution and record it in the Table 1 below.
  • Add all of the Solid L provided at once and start a stop watch immediately.
  • Using a thermometer, Stir the mixture thoroughly and continuously and record the temperature of the mixture after every one minute in the table 1.
  • Retain the resultant mixture for use in the next Procedure II.

Table 1

Time (Min) 0 1 2 3 4 5 6 7 8 9 10
Temperature(0C) 21.0 22.5 24.0 25.0 27.0 28.0 29.5 31.0 31.0 31.0 29.5

ct - 1, D - 1/2, AC - 1, Trend - 1/2

(3 marks)

  1. Plot a graph of temperature (vertical axis) against time on the grid provided below. (3 marks)
  2. From the graph you have drawn, determine the;
    1. highest change in temperature, ∆T (1 mark)

      32.6-21.0 = 11.6oC or 11.6K
      (Must be shown on graph)

    2. time taken for the reaction to completely occur (1 mark)

      8 minutes
      (must be shown on graph)


  3. Calculate the heat change for the reaction. (Take density of the solution to be 1g/cmand specific heat capacity of the solution to be 4200kJ/Kg/K)  (2 marks)

Procedure II

  • Swirl the mixture obtained in procedure I above and filter into a 250mL volumetric flask.
  • Thoroughly rinse the beaker with 20cm3 of distilled water and ensure all the mixture has been transferred onto the filter paper.
  • Add 50cm3 of 2M Sulphuric (VI) acid to the filtrate mixture in the volumetric flask.
  • Add more distilled water to the solution in the volumetric flask to the mark. Mix the contents thoroughly and label this solution as Solution N.
  • Fill the burette with Solution M.
  • Place 25 cm3 of Solution N into a 250 cm3 conical flask using a pipette and a pipette filler.
  • Titrate Solution N against Solution M until the first permanent pink colour is seen.
  • Record your results in Table 2
  • Repeat the titration twice and complete Table 2.

Table 2

Titre I II III
Final burette reading(cm3) 20.5 20.2 40.3
Initial burette reading (cm3) 0.0 0.0 20.2
Volume of solution M used (cm3) 20.5 20.2 20.1

(3 marks)
CT = 1, AC = 1, D = 1/2, PA = 1/2, FA = 1

  1. What is the average volume of Solution M used? (1 mark)

    (20.2 + 20.1)/2 = 20.15

  2. Calculate the molarity of Solution M, KMnO4 (1 mark) (K=39, Mn=55, O=16)
    1iichemsp3
  3. Calculate the number of moles of:
    1. Potassium manganate (VII) used, solution M   (1 mark)
      1iiiachemsp3
    2. Iron (II) ions in 25cm3 of solution N      (1 mark)

      The equation for the reaction is:

      MnO4-(aq) + 8H+ (aq) + 5Fe2+ (aq)        ->         Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)

      1iiibchemsp3

    3. Iron (II) ions in the 250cm3 of solution N (1 mark)
      1iiicchemsp3
  4. Determine the molar heat of displacement of copper from a solution of its ions by iron metal (2 marks)
    1ivchemsp3
  5. Draw an energy level diagram for the reaction      (2 marks)

    1vchemsp3

Question 2

  1. You have been provided with solutions X, Y and Z. Carry out the flame tests for each and indicate the colour of the flames and inferences below.(3 marks)

     

    Ions Flame Colour Inference
    X Purple flame K+ present
    Y Yellow flame Na+ present
    Z Green flame Cu2+ present
  2. You are provided with Solid Q. Carry out the tests below and Write your observations and inferences in the spaces provided.
    1. Place all Solid Q in a clean test tube. Add about 8cm3 of distilled water and shake. Divide the solution into 3 portions
      Observation Inference
      Dissolves to form a colourless solution(1/2 mark)   -Polar substance/soluble substance
      -Absence of Cu2+, Fe2+, Fe3+(1/2 mark)
    2. To the first portion add a few drops of Lead (II) nitrate solution and warm
      Observation Inference
      White precipitate, insoluble on warming(1 mark)   CO32-, SO42-, SO32- present(1 mark)
    3. To the first portion add a few drops of Barium nitrate solution followed by few drops of dilute hydrochloric acid.
      Observation Inference
      -White precipitate soluble in the acid to form a colourless solution.
      -Effervescence of a colourless gas (1 mark)  
      CO32-,SO32-(1 mark)
    4. To the third portion add a few drops of acidified potassium dichromate (VI) then warm gently.
      Observation Inference
      Orange H+/K2Cr2O7 turns green(1 mark)   SO32- present(1 mark)
  1. You have been provided with Liquid E.
    1. Place about 2cm3 of the Liquid E in a clean test tube. Add an equal amount of distilled water and shake the mixture. Allow to settle.
      Observation Inference
      Miscible with water/ forms uniform mixture(1 mark)   Liquid E is polar(1 mark)
    2. Place about 2cm3 of the Liquid E in a clean test tube. Add a half spatulaful of sodium hydrogen carbonate.
      Observation Inference
      No fizzling/no bubbles or no effervescence or a colourless gas(1 mark)   RCOOH, H+, H3O+,COOH absent(1 mark)
    3. To about 2cm3 the Liquid E add 3 drops of acidified potassium dichromate (VI) solution and warm gently.
      Observation Inference
      Colour of H+/K2Cr2O7 changes from orange to green. (1 mark)   ROH present(1 mark)
    4. Take a few drops of Liquid E on a clean and dry metallic spatula and ignite over a non-luminous Bunsen flame.
      Observation Inference
      Burns with a blue non-sooty/non-smoky flame(1 mark)   ROH confirmed(1 mark)

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