Chemistry Paper 3 Questions and Answers - Kassu Jet Joint Exams 2020/2021

Share via Whatsapp

INSTRUCTIONS TO CANDIDATES:

  • Answer all the questions in the spaces provided in the question paper.
  • You are NOT allowed to start working within the first 15 minutes of the 2¼ hours allowed for this paper. This time is to enable you read the question paper and make sure you have all the chemicals and apparatus that you may need.
  • All working MUST be clearly shown.
  • Mathematical tables and silent scientific calculators may be used.


QUESTIONS

  1. You are provided with:
    • 5.0g of solid X in a boiling tube
    • Solution Y, which is acidified Potassium manganate (VII) containing 9.0g of Potassium manganate (VII), KMnO4, in 1000cm3 of solution.

    You are required to determine:
    1. The solubility of solid X at different temperatures
    2. The number of moles of water of crystallization in solid X

    Procedure I
    1. Using a 10 cm3 measuring cylinder add 4cm3 of distilled water to solid X in the boiling tube. Heat the mixture while stirring with the thermometer to about 850C.When all the solid has dissolved allow the solution to cool while stirring with the thermometer.(You can occasionally immerse the boiling tube in a beaker of tap water). Note the temperature at which crystals of solid X first appear. Record this temperature in table 1.
    2. Add 2cm3 of distilled water to the contents of the boiling tube warm the mixture while stirring with the thermometer until all the solid dissolves. Allow the mixture to cool while stirring. Note and record the temperature at which crystals of solid X first appear.
    3. Repeat procedure (ii) three more times and record the temperature in the table 1. Retain the contents of the boiling tube for use in the procedure (v).
    4.  
      1. Complete table 1 by calculating the solubility of solid X at different temperatures.

        Table 1
         Volume of water (cm3)  Temperature at which crystals(0C)  Solubility of solid X (g/100g of water)
         4    
         6    
         8    
         10    
         12    
        (6 marks)
      2. On the grid provided, plot a graph of solubility of solid X (vertical axis) against temperature. (3 marks)
      3. Using your graph, determine the temperature at which 100g of solid X would dissolve in 100cm3 of water. (1 mark)

    Procedure II

    1.  
      1. Transfer the contents of the boiling tube into a 250ml volumetric flask, rinse both the boiling tube and the thermometer with distilled water and add to the volumetric flask. Add more distilled water to make up to the mark. Label this solution X. Fill a burette with solution Y.
        Using the pipette and pipette filler, place 25.0cm3 of solution X into a conical flask. Warm the mixture to about 600C. Titrate the hot solution X with solution Y until a permanent pink colour persists. Continuously shake the mixture during the titration. Record your readings in table 2.
        Repeat the titration two more times and complete the table 2.

        Table 2
         Titration  I  II  III
         Final burette reading (cm3)      
         Initial burette reading (cm3)      
         Volume of solution Y used (cm3)      
        (4 marks)
      2. Calculate the:
        1. average volume of solution Y used (1 mark)
        2. Number of moles of Solution Y, Potassium manganate (VII) used (K=39, Mn=55, O=16) (2 marks)
        3. Number of moles of X in 25cm3 of solution X given that 2 moles of potassium manganate (VII) react completely with 5 moles of X (1 mark)
        4. Number of moles of X in 250cm3 of solution (1 mark)
        5. Relative formula mass of X, (1 mark)
      3. The formula of X has the form X.nH2O. Determine the value of n in the formula given that the relative mass of X is 90.0 (O=16.0, H=1.0) (2 marks)
  2. You have been provided with solid R. Carry out the tests below
    1. Transfer all the solid R to a boiling tube. Add about 6cm3 of distilled water and shake the mixture thoroughly. Allow to settle then carefully filter into another boiling tube. Retain the residue for part (b)
      Divide the filtrate into three portions
      1. To the first portion of the filtrate in a test tube, add few drops of 2M lead (II) nitrate solution and warm
         Observations  Inferences

         1 mark

         ½ mark

      2. To the second portion of the filtrate in a test tube, add 2M sodium hydroxide solution drop wise until in excess
         Observations  Inferences

         1 mark

         1 mark

      3.  
        1. Describe how you would carry out a flame test on the solution obtained.
           Procedure  Expected observation

           1 mark

           1 mark

        2. On the third portion of the filtrate, carry out the flame test described above
           Observations  Inferences

           ½ mark

           ½ mark

    2.  
      1. To the residue in a boiling tube add 2M hydrochloric acid provided drop wise until there is no more change. Test for any gas using a burning splint.
        Divide the resultant solution into two portions
         Observations  Inferences

         1 mark

         ½ mark

      2. To the first portion, add 2M sodium hydroxide solution drop wise until in excess
         Observations  Inferences

         1 mark

         ½ mark

      3. To the second portion, add 2M ammonium hydroxide solution until in excess
         Observations  Inferences

         1 mark

         ½ mark

  3. You are provided with solid H. Carry out the tests below. Write your observations and inferences in the spaces provided.
    1. Using a clean metallic spatula, heat about one third of solid H in a Bunsen burner flame.
       Observations  Inferences

       1 mark

       1 mark



    2. Dissolve the remaining portion of solid H by adding about 6cm3 of distilled water and divide the solution into 3 portions.
      1. To the first portion, add two drops of acidified potassium manganate (VII) solution
         Observations  Inferences

         1 mark

         1 mark

      2. To the second portion, add two drops of bromine water
         Observations  Inferences

         1 mark

         1 mark

      3. Determine the pH of the third portion using universal indicator paper
         Observations  Inferences

         1 mark

         1 mark



Marking Scheme

  1. You are provided with:
    • 5.0g of solid X in a boiling tube
    • Solution Y, which is acidified Potassium manganate (VII) containing 9.0g of Potassium manganate (VII), KMnO4, in 1000cm3 of solution.
    You are required to determine:
    1. The solubility of solid X at different temperatures
    2. The number of moles of water of crystallization in solid X

    Procedure I
    1. Using a 10 cm3 measuring cylinder add 4cm3 of distilled water to solid X in the boiling tube. Heat the mixture while stirring with the thermometer to about 850C.When all the solid has dissolved allow the solution to cool while stirring with the thermometer.(You can occasionally immerse the boiling tube in a beaker of tap water). Note the temperature at which crystals of solid X first appear. Record this temperature in table 1.
    2. Add 2cm3 of distilled water to the contents of the boiling tube warm the mixture while stirring with the thermometer until all the solid dissolves. Allow the mixture to cool while stirring. Note and record the temperature at which crystals of solid X first appear.
    3. Repeat procedure (ii) three more times and record the temperature in the table 1. Retain the contents of the boiling tube for use in the procedure (v).
    4.  
      1. Complete table 1 by calculating the solubility of solid X at different temperatures.

        Table 1

         Volume of water (cm3)  Temperature at which crystals(0C)  Solubility of solid X (g/100g of water)
         4  79  125.00 ✓½
         6  67  83.333 ✓½
         8  55  62.500 ✓½
         10  52  50.000 ✓½
         12  48  41.667 ✓½

        - Accuracy (79 ± 2oC) - 1
        - Decimal - 1
        - Trend - ½
        - Complete table - 1
        - Calculations (solubility column) - 2½
        Total = 6
      2. On the grid provided, plot a graph of solubility of solid X (vertical axis) against temperature. (3 marks)
      3. Using your graph, determine the temperature at which 100g of solid X would dissolve in 100cm3 of water. (1 mark)
        70oC ✓½ Must be shown on the graph

    Procedure II

    1.  
      1. Transfer the contents of the boiling tube into a 250ml volumetric flask, rinse both the boiling tube and the thermometer with distilled water and add to the volumetric flask. Add more distilled water to make up to the mark. Label this solution X. Fill a burette with solution Y.
        Using the pipette and pipette filler, place 25.0cm3 of solution X into a conical flask. Warm the mixture to about 600C. Titrate the hot solution X with solution Y until a permanent pink colour persists. Continuously shake the mixture during the titration. Record your readings in table 2.
        Repeat the titration two more times and complete the table 2.

        Table 2

         Titration  I  II  III
         Final burette reading (cm3)  27.4  27.4  27.4
         Initial burette reading (cm3)  0.0  0.0   0.0
         Volume of solution Y used (cm3)  27.4  27.4  27.4

        CT  -  1
        D  -    1
        AC  -  1
        PA  -  1
        FA  -  1
                 5
        (4 marks)
      2. Calculate the:
        1. average volume of solution Y used (1 mark)
          I + II + III  = Ans e.g. 27.4 + 27.4 + 27.4 = 27.4
                 3                                     3   
               
        2. Number of moles of Solution Y, Potassium manganate (VII) used (K=39, Mn=55, O=16) (2 marks)
          KMnO4 = 158
          Molarity = 9/158 = 0.057M
          Moles = Ans b(I) ÷ 1000 ✓½
          = Ans b(II) ✓½
          e.g. 27.4 × 0.057 = 0.0015661 Mol
                1000
        3. Number of moles of X in 25cm3 of solution X given that 2 moles of potassium manganate (VII) react completely with 5 moles of X (1 mark)
          MnO4-:X = 2:5
          Moles of X in 25 cm3 = 5/2 × Ans b(II) ✓½
          = Ans b (III) ✓½
          e.g. 5/2 × 0.001561 ✓½
          = 0.003902 ✓½
        4. Number of moles of X in 250cm3 of solution (1 mark)
          250/25 × Ans bIII ✓½            e.g. 250/25 × 0.003902
          = Ans b(IV)                               = 0.03902 ✓½
        5. Relative formula mass of X, (1 mark)
          5/Ans b(IV) ✓½     e.g. 5/0.03902
          = Ans b(V) ✓½   
          = 128.1427
      3. The formula of X has the form X.nH2O. Determine the value of n in the formula given that the relative mass of X is 90.0 (O=16.0, H=1.0) (2 marks)
        x.nH2O = Ans b(V) ✓½
        n = (ans b(V) − 90 ÷ 18 ✓½
        = Ans (c)
        e.g. 90 + 18n = 128.1427 ✓½
        18n = 128.1427 − 90 
        n = 38.1427 ÷ 18 ✓½
        = 2.12 ≈ 2 ✓1
  2. You have been provided with solid R. Carry out the tests below
    1. Transfer all the solid R to a boiling tube. Add about 6cm3 of distilled water and shake the mixture thoroughly. Allow to settle then carefully filter into another boiling tube. Retain the residue for part (b)
      Divide the filtrate into three portions
      1. To the first portion of the filtrate in a test tube, add few drops of 2M lead (II) nitrate solution and warm
         Observations  Inferences

        White ppt ✓½ soluble on warming ✓½

         Cl-, Br- present
         Any 1 × ½
        Penalize fully for contradiction

      2. To the second portion of the filtrate in a test tube, add 2M sodium hydroxide solution drop wise until in excess
         Observations  Inferences

        White ppt insoluble in excess ✓1

        Mg2+, Ca2+
        2 - 1 mark
        1 - ½ mark
        0 - 0 mark
        penalize ½ mark for each contradiction upto 1 mark max

      3.  
        1. Describe how you would carry out a flame test on the solution obtained.
           Procedure  Expected observation

          Dip a clan nichrome wire or metallic spatula into the solution ✓½
          Heat the part with solution on a non-luminous flame ✓½ 

           Flame color is bright white or orange

        2. On the third portion of the filtrate, carry out the flame test described above
           Observations  Inferences

          Orange flame

          Ca2+ (Must have appeared in 2a(ii), procedure in 2 (iii) must be correct
          penalize fully for any contradiction 

    2.  
      1. To the residue in a boiling tube add 2M hydrochloric acid provided drop wise until there is no more change. Test for any gas using a burning splint.
        Divide the resultant solution into two portions
         Observations  Inferences

        Bubbles/effervescenece of colourless gas✓½
        Colourless solution formed ✓½

        CO32- (reject HCO3-)
        Cu2+, Fe2+, Fe3+ absent 
        Any correct pegged on correct observation

      2. To the first portion, add 2M sodium hydroxide solution drop wise until in excess
         Observations  Inferences

        White ppt✓½ soluble ✓½ in excess

         Zn2+, Pb2+✓½
         2 ions - ✓½
         1,0 - 0 mark
         penalize fully for wrong symbol, wrong ion

      3. To the second portion, add 2M ammonium hydroxide solution until in excess
         Observations  Inferences

         White ppt soluble in excess ✓1

         Zn2+ present
         Must have appeared in b(ii) above
         Penalize fully for any contradiction to ½mark maximum 

  3. You are provided with solid H. Carry out the tests below. Write your observations and inferences in the spaces provided.
    1. Using a clean metallic spatula, heat about one third of solid H in a Bunsen burner flame.
       Observations  Inferences

       Burns with yellow smoky/sooty flame ✓1  

          |   |
       —C=C—/—C≡C—/long chain hydrocarbon

    2. Dissolve the remaining portion of solid H by adding about 6cm3 of distilled water and divide the solution into 3 portions.
      1. To the first portion, add two drops of acidified potassium manganate (VII) solution
         Observations  Inferences

         Purple H+/KMnO4 is decolourized ✓1 

            |   |
         —C=C—/—C≡C—✓½, ROH✓½

      2. To the second portion, add two drops of bromine water
         Observations  Inferences

         Yellow/orange decolourised ✓1

            |   |
         —C=C—/—C≡C— Present 1

      3. Determine the pH of the third portion using universal indicator paper
         Observations  Inferences

         pH = 1,2,3 ✓½

         Strong acidic ✓½



CONFIDENTIAL

Instructions to Schools:

The information contained in this paper is to enable the head of the school and the teacher in charge of Chemistry to make adequate preparation for the Chemistry Practical Examination.

NO ONE ELSE should have access to this paper or acquire knowledge of its content. Great care MUST be taken to ensure that the information herein does NOT reach the candidates either directly or indirectly. The teacher in charge of Chemistry should NOT perform any of the experiments in the SAME room as the candidates nor make the results of the experiment available to the candidates of give any information related to the experiments to the candidates. Doing so will constitute an examination irregularity.

In addition to the fittings and apparatus found in a Chemistry laboratory, EACH candidate will require:

  1. 100ml of Solution Y for each candidate
  2. Accurately weighed 5g of solid X supplied in a stoppered container.
  3. About 0.5g of Solid H supplied in a stoppered container.
  4. About 1g of solid R supplied in a stoppered container.
  5. One Burette, 0-50ml.
  6. One 25ml Pipette.
  7. Three 250ml Conical Flasks
  8. 250ml Volumetric Flask with a stopper.
  9. One complete Retort Stand
  10. One White Tile
  11. One Pipette Filler
  12. One Test-tube Rack
  13. Six Test-tubes (on a rack)
  14. Source of heat
  15. Tripod stand
  16. Wire gauze
  17. Clean metallic spatula
  18. Wooden splint
  19. Clean glass rod or Nichrome wire loop
  20. Thermometer with a range of -100C to 110 0C
  21. 200cm3 beaker
  22. Test tube holder
  23. One label
  24. Two Boiling tubes
  25. One Filter paper
  26. Filter funnel
  27. Measuring cylinder 10ml
  28. Wash bottle filled with distilled water

ACCESS TO

  1. Acidified Potassium Manganate (VII) supplied with a dropper.
  2. Universal indicator paper
  3. PH chart
  4. 2M Hydrochloric acid supplied with a dropper.
  5. 2M Sodium hydroxide solution supplied with a dropper.
  6. 2M Ammonia solution supplied with a dropper.
  7. 2M lead (II) nitrate supplied with a dropper.
  8. Bromine water supplied with a dropper.

NOTES

  1. Solution Y -Acidified Potassium Manganate (VII)prepared by dissolving 9g of solid Potassium Manganate (VII) in about 600cm3 of 2M Sulphuric (VI) acid and adding distilled water to make a litre of solution.
  2. Solid H is pure Maleic acid.
  3. Solid R is a 1g mixture of anhydrous calcium chloride and zinc carbonate in the ratio of 1:1
  4. Solid X is accurately weighed 5g of Oxalic acid

Download Chemistry Paper 3 Questions and Answers - Kassu Jet Joint Exams 2020/2021.


Tap Here to Download for 50/-




Why download?

  • ✔ To read offline at any time.
  • ✔ To Print at your convenience
  • ✔ Share Easily with Friends / Students


Join our whatsapp group for latest updates
Get on WhatsApp Download as PDF
.
Subscribe now

access all the content at an affordable rate
or
Buy any individual paper or notes as a pdf via MPESA
and get it sent to you via WhatsApp

 

What does our community say about us?

Join our community on:

  • easyelimu app
  • Telegram
  • facebook page
  • twitter page
  • Pinterest