Chemistry Paper 3 Questions and Answers with Confidential - Kassu Joint Mock Examination 2021

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 2 ¼ 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.
• This paper consists of 7 printed pages.
• Candidates should check to ascertain that all papers are printed as indicated and that no questions are Missing

QUESTIONS

1. You are provided with:
   
   1. 5.0g of solid X in a boiling tube
   2. 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

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 thethermometer to about 85ºC.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
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(ºC)	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
5.         
   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 60ºC. 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)	(1/2 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
            (1 mark)	(1/2 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)	(1/2 mark)

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

         Observations	Inferences
         (1 mark)	(1/2 mark)

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

         Observations	Inferences
         (1 mark)	(1/2 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
         (1/2 mark)	(1/2 mark)

CONFIDENTIAL INSTRUCTIONS

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 -10ºC to 110ºC
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

MARKING SCHEME

1. You are provided with:
   
   1. 5.0g of solid X in a boiling tube
   2. 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

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 thethermometer to about 85ºC.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
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(ºC)	Solubility of solid X (g/100g of water)
      4	79	125.000
      6	67	83.333
      8	55	62.500
      10	52	50.000
      12	48	41.667

      (6 marks)
      
      • Accuracy(79±2ºC) - 1mk
      • Decimal - 1mk
      • Trend - 1/2 mk
      • Complete table - 1
      • Calculations (solubility column) - 2.5mks
   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 (Must be shown on graph)
      
      Procedure II
5.         
   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 60ºC. 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

      (4 marks)
   2. Calculate the:
      
      1. average volume of solution Y used (1 mark)
         I + II + III = Ans bI   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 bI x 0.057) ÷1000
         = ans bII 
         e.g. 27.4  x 0.057 = 0.001561mol
               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 25cm³ = ⁵/₂ x ans bII
         =Ans bIII
         e.g. ⁵/₂ x 0.001561
         =0.003902
      4. Number of moles of X in 250cm³ of solution (1 mark)
         250 x Ans bIII 
          25
         =Ans b(IV) 
         e.g.     5      
              0.03902
         = 0.03902
      5. Relative formula mass of X, (1 mark)
              5      
         Ans b IV
         = Ans bIV
         e.g      5      
              0.03902
         = 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) 
      n = (Ans b(v) - 90) ÷ 18
      = Ans (c)
      e.g. 90 + 18n = 128.1427
      18n = 128.1427 - 90
      n = 38.1427 ÷ 18
      = 2.12 ≈ 2

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 soluble on warming	Cl-, Br- present  (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	Mg2+, Ca 2 - 1 mark 1 - 1/2 mark 0 - 0 mark

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

            Procedure	Expected observation
            Dip a clean glandrod,/nichome wire/metallis spatula into the solution  Heat the part with solution on a non-luminous flame	Flame color in 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 a (ii), procedure in 2(iii) must be correct.  Penalise 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 of colorless gas colorless solution formed	CO32- (reject HCO3) Cu2+, Fe2+, Fe3+ absent Any 1 correct or pegged on correct observation

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

         Observations	Inferences
         White ppt soluble in excess	Zn2+, pb2+ present 2 - 1/2 mark 1 - 0 mark

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

         Observations	Inferences
         White ppt soluble in excess	Zn2+ present Must have appeared in b(iii) above Penalise fully for any contradiction to 1/2 mark 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

   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
         People H+/Kmn 04 in decolorized

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

         Observations	Inferences
         Yellow/orange decolorised

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

         Observations	Inferences
         PH = 1,2,3	Strongly acidic