Chemistry Paper 3 Questions and Answers with Confidential - Samia Joint Mock Examination 2021/2022

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INSTRUCTIONS TO CANDIDATES

  • Write your name, School and Index Number in the spaces provided above.
  • Sign and write date of examination in the spaces provided above.
  • Answer ALL questions in the spaces provided.
  • You are not allowed to start working with the apparatus for the first 15 minutes of the 2¼ 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 that you may need.
  • Mathematical tables and electronic calculators may be used.
  • All working MUST be clearly shown where necessary.
  • This paper contains 9 printed pages
  1. You are provided with :
    Solution Q, 2M Hydrochloric acid.
    Solution P, 0.15M Sodium thiosulphate
    Solution R, Sodium carbonate
    Procedure 1
    Measure 20cm3 of 0.15M Sodium thiosulphate (solution P) into a 100cm3 a glass beaker. Place the beaker on a white piece of paper with ink mark ‘X’ on it. Measure 20cm3 of 2M hydrochloric acid solution Q using a 50cm3 measuring cylinder. Put the acid into the glass beaker containing Sodium thiosulphate and immediately start off the stop watch. Determine the time taken for the marks ‘X’ to become invisible/obscured when viewed from above. Repeat the procedure by measuring different volumes of the acid and adding the volume of the distilled water to complete table 1 below.
    Table 1
    Volume of acid(cm3) Volume of water(cm3) Volume of sodium thiosulphate (cm3) Time taken for mark ‘X’ to be invisible/obscured(seconds) Reciprocal of time (sec-1I/T
    20 0 20    
    18 2 20    
    16 4 20    
    14 6 20    
    12 8 20    
    10 10 20    
    1. Complete the table below (6mks)
    2. Plot a graph of I/T(rate) against volume of acid used. (3mks)
    3. Explain the shape of your graph (1mk)
    4. From the graph determine;
      1. Time taken for the cross to be obscured/invisible when the volume of the acid is:
        15cm3 (1mk)
        8cm3 (1mk)
      2. The volume of the acid used if the time taken for the cross to be obscured/invisible is:
        40seconds (1mk)
        43 seconds (1mk)

        Procedure 2
        Using a 10cm3 measuring cylinder, place 10cm3 of solution Q into a 250ml volumetric flask. Add about 200cm3 of distilled water. Shake well. Add more distilled water to top up to the mark. Labeled this solution T. Fill the burette with solution T. using a pipette and pipette filler, pipette 25cm3 of solution R into a conical flask. Add 3 drops of phenolphthalein and titrate with solution T.
        • Record your results in the table
        • Repeat the titration two more times and complete the table
          Table 2
            II III
          Final burette reading(cm3)      
          Initial burette reading(cm3)      
          Volume of solution T (cm3) added      
          (4mks)
        • Determine the :
          Average volume of solution T used (1mk)
          Moles of the acid in the average volume of solution T used. (2mk)
          Concentration of solution R in moles per litre. (2mks)
  2.      
    1. Put a spatula end-full of solid A into a boiling tube and about 10cm3 of distilled water. Shake the mixture well. Divide the resultant solution into 4 equal portions.
      Observation Inferences
         
    2. To the first portion, add a little calcium hydroxide solid and warm. Test any gases produced using both blue and red litimus paper.
      Observation Inferences
         
    3. To the second portion, add 4 drops of hydrogen peroxide solution. Test the gas produced using a glowing splint.
      Observation Inferences
         
    4.            
      1. The solution is also suspected to contain sulphite ions. Using Barium nitrate solution and dilute hydrochloric acid solution. Describe how you would confirm presence of the sulphite ions.
        Observation Inferences
           
      2. Carry out the actual test as described in (d) (i) above
        Observation Inferences
           
  3. You are provided with solid B. carry out the tests below and record your observation and inferences in the spaces provided.
    1. Place one third of solid B on a metallic spatula. Burn it in a non-luminous flame of the Bunsen burner.
      Observation Inferences
         
    2. Place the remaining solid in a test-tube. Add about 6cm3 of distilled water and shake the mixture well. Divide the resulting mixture into 4 portions.
      Observation Inferences
         
      1. To the first portion, add 2 drops of acidified potassium manganite (VII)
        Observation Inferences
           
      2. To the second portion, add 3 drops of acidified potassium dichromate (VI) and warm
        Observation Inferences
           
      3. To the third portion, add 1g of solid sodium hydrogen carbonate.
        Observation Inferences
           
      4. To the fourth portion, add 5 drops of ethanol followed by few drops of dilute sulphuric (VI)acid and warm
        Observation Inferences
           

CONFIDENTIAL
Apart from the usual laboratory fittings, each student should have the following:

  1. About 0.5g of solid A in a stoppered container
  2. About 0.5g of solid B in a stoppered container
  3. 100cm3 of solution R
  4. 150cm3 of solution Q
  5. 150cm3 of solution P
  6. Distilled water in a wash bottle
  7. About a spatula end –full of solid Calcium Hydroxide
  8. Red and blue litimus papers
  9. Three 250ml conical flasks
  10. One burette0-50ml
  11. One pipette 25ml
  12. One 50ml measuring cylinder
  13. One 10ml measuring cylinder
  14. One 25cm3 volumetric flask
  15. Phenolphthalein indicator
  16. Labels (2)
  17. Stop watch
  18. Two boiling tubes
  19. One metallic spatula
  20. Five test tubes on a test-tube rack
  21. Wooden splint
  22. Test tube holder
  23. 100ml glass beaker
  24. 1g sodium hydrogen carbonate
  25. White paper
  26. Filter funnel

The student should also get access to:

  1. 10% Hydrogen peroxide (freshly prepared + dropper).
  2. 2M Barium nitrate solution +dropper
  3. 0.5M Hydrochloric acid + dropper
  4. Source of heat
  5. Acidified potassium manganite (VII)
  6. Acidified potassium dichromate (VI)
  7. 2M dilute sulphuric (VI) acid
  8. Ethanol with a dropper

NOTES

  • Solid A is Hydrated ferrous ammonium sulphate
  • Solution B is Melleic acid
  • Solution R is prepared by welghing exactly 4.8g of sodium carbonate dissolves it to make 1dm3 of solution
  • Solution Q is prepared by weighing exactly 172cm3 of hydrochloric acid (35-37% sp.gr 1.18)and dissolving to make 1dm3 of solution
  • Solution P is prepared by weighing exactly 37.2g of sodium thiosulphste pentahydrate and dissolving to make 1dm3 of solution.

MARKING SCHEME

  1. You are provided with :
    Solution Q, 2M Hydrochloric acid.
    Solution P, 0.15M Sodium thiosulphate
    Solution R, Sodium carbonate
    Procedure 1
    Measure 20cm3 of 0.15M Sodium thiosulphate (solution P) into a 100cm3 a glass beaker. Place the beaker on a white piece of paper with ink mark ‘X’ on it. Measure 20cm3 of 2M hydrochloric acid solution Q using a 50cm3 measuring cylinder. Put the acid into the glass beaker containing Sodium thiosulphate and immediately start off the stop watch. Determine the time taken for the marks ‘X’ to become invisible/obscured when viewed from above. Repeat the procedure by measuring different volumes of the acid and adding the volume of the distilled water to complete table 1 below.
    Table 1
    Volume of acid(cm3) Volume of water(cm3) Volume of sodium thiosulphate (cm3) Time taken for mark ‘X’ to be invisible/obscured(seconds) Reciprocal of time (sec-1) I
    Volume of acid(cm3) Volume of water(cm3) Volume of sodium thiosulphate (cm3) Time taken for mark ‘X’ to be invisible/obscured(seconds) Reciprocal of time (sec-1I/T
    20 0 20 33 0.0301
    18 2 20 37 0.0270
    16 4 20 41 0.0240
    14 6 20 47 0.0210
    12 8 20 57 0.0180
    10 10 20 63 0.0160
    1. Complete the table below (6mks)
      CT 1
      DP ½
      AC ½
      TREND 1
      Calculations of R ½ for each calculation done correctly.
    2. Plot a graph of I/t (rate) against volume of acid used. (3mks)
      L ½
      S ½
      P ½
      Line 1
      03
      The graph must be a straight line from the origin, otherwise award zero for the line
    3. Explain the shape of your graph (1mk)
      • Straight line graph from the origin ½ increase in volume of HCI increases rate of reaction I/t
      • This is due to increase in the number of reacting particles hence more successful collisions. ½
    4. From the graph determine;
      1. Time taken for the cross to be obscured/invisible when the volume of the acid is:
        15cm3(1mk)
        • Showing on a correctly plotted graph
        • If graph is not correctly plotted, penalize fully
          8cm3 (1mk)
        • Some applies as in (i) above.
      2. The volume of the acid used if the time taken for the cross to be obscured/invisible is:
        40seconds (1mk)
        • Same to (i)
          43 seconds (1mk)
        • Same to (i)
          Procedure 2
          Using a 10cm3 measuring cylinder, place 10cm3 of solution Q into a 250ml volumetric flask. Add about 200cm3 of distilled water. Shake well. Add more distilled water to top up to the mark. Labeled this solution T. Fill the burette with solution T. using a pipette and pipette filler, pipette 25cm3 of solution R into a conical flask. Add 3 drops of phenolphthalein and titrate with solution T.
          1. Record your results in the table
          2. Repeat the titration two more times and complete the table
            Table 2
              II III
            Final burette reading(cm3) 15.0 15.0 15.0
            Initial burette reading(cm3) 0 0 0
            Volume of solution T (cm3) added 15.0 15.0 15.0
        • Determine the :
          Average volume of solution T used (1mk)
          15.0 +15.0 +15.0 ½
          3
          =15.0cm3 ½
          Moles of the acid in the average volume of solution T used. (2mk)
          M1V1 =M2V2
          M2 =  10×2 
                  250cm3 ½
          =0.08M ½
          No. of moles= 0.08×15.0 ½
                                     1000
          = 0.0012moles ½
          Accept any other correct method
          Concentration of solution R in moles per litre. (2mks)
          Na2CO3(s) +2HCI(aq) 2NaCI(aq) + CO2(g) +H2O(I)
          No. of moles in Na2CO3 =0.0012
                                                       2
          =0.0006 moles ½
          Or answer in (iii) =answer in (ii) 
                                                        2
          M=0.0006×1000 1mark
                        25
          = 0.024M ½
  2.    
    1. Put a spatula end-full of solid A into a boiling tube and about 10cm3 of distilled water. Shake the mixture well. Divide the resultant solution into 4 equal portions.
      Observation Inferences
      Solid A dissolves to form a pale green solution.(½mk) Cu2+ and Fe2+ present(1mk)
    2. To the first portion, add a little calcium hydroxide solid and warm. Test any gases produced using both blue and red litimus paper.
      Observation Inferences
      Red litmus paper turns ½
      Blue litmus paper venaire blue ½(1mk)
      NH4+ present(1mk)
    3. To the second portion, add 4 drops of hydrogen peroxide solution. Test the gas produced using a glowing splint.
      Observation Inferences
      - Pale green solution turns brown ½
      - Colourless gas relights a glowing splint ½
      (1mk) 
      Fe2+ oxidized to Fe3+
      (must have appeared in (a) and tied to pale green turns brown in observation )
       
    4.      
      1. The solution is also suspected to contain sulphite ions. Using Barium nitrate solution and dilute hydrochloric acid solution. Describe how you would confirm presence of the sulphite ions.
        Observation Inferences
        To the third portion add 3 drops of Ba(NO3)2 followed by 3 drops of HCI(aq) ½ (1mk)  White precipitate soluble on addition of dilute HCI(aq)(1mk)

      2. Carry out the actual test as described in (d) (i) above
        Observation Inferences
        White precipitate insoluble on addition of HCI (1mk)  SO42- Present (1mk) 
  3. You are provided with solid B. carry out the tests below and record your observation and inferences in the spaces provided.
    1. Place one third of solid B on a metallic spatula. Burn it in a non-luminous flame of the Bunsen burner.
      Observation Inferences
      Solid B melts and burns with yellow sooty flame (1mk) 1
    2. Place the remaining solid in a test-tube. Add about 6cm3 of distilled water and shake the mixture well. Divide the resulting mixture into 4 portions.
      Observation Inferences
      Solid B dissolves to form a colourless solution (½mk)  Polar organic compound. (½mk)
      1. To the first portion, add 2 drops of acidified potassium manganite (VII)
        Observation Inferences
        Purple KMnO4/H+ turns colourless
        Or
        Purple KMnO4/H+ is decolourised (1mk) 
        R-OH presnt(1mk)
        2 
      2. To the second portion, add 3 drops of acidified potassium dichromate (VI) and warm
        Observation Inferences
        Orange colour of K2Cr2O7/H+ is retained/persists/remains orange/Does not turn to green
        (1mk) 
        R-OH absent (1mk)

      3. To the third portion, add 1g of solid sodium hydrogen carbonate.
        Observation Inferences
        Effervescence/bubbles/fizzing
        Reject
        Fizzling
        Hissing
        (½mk) 
        H+/R-COOH/H3O+ present (½mk)




      4. To the fourth portion, add 5 drops of ethanol followed by few drops of dilute sulphuric (VI)acid and warm
        Observation Inferences
        Pleasant smell
        Fruity smell
        Reject : Sweet smell
        (½mk) 
        R-COOH Present (½mk) 

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