Chemistry Paper 3 Questions and Answers - Maranda High Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES 

• Answer ALL questions in the spaces provided on the question paper
• 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 apparatus and chemicals that you may need.
• All working MUST be clearly shown where necessary
• Mathematical tables and silent non-programmed electronic calculators may be used.

Question 1

You are provided with: 

• Solid A – 6.2g of an alkanoic acid in a boiling tube. 
• Solution B – 2.0M sodium hydroxide solution.
  You are required to;
  1. Determine the solubility of solid A at different temperatures.
  2. Find the molar mass of alkanoic acid. 

Procedure I 

1. Using a burette, add 10cm³of distilled water to solid A in the boiling tube. Heat the mixture while stirring with the thermometer to about 75^oC. When the entire solid has dissolved, allow the solution to cool while stirring with the thermometer. Note the  temperature at which crystals of solid A appear. Record this temperature in table 1.
2. Using the burette, add 2cm³of distilled water to the contents of the boiling tube. Warm  the mixture while stirring with the thermometer until the solid dissolves. Allow the  mixture to cool while stirring. Note the temperature at which crystals of solid A appear.
3. Repeat procedure (b) two more times and record the thermometer readings in table I.  Retain the contents of the boiling tube for use in procedure II. 
   1. Complete table 1 by calculating the solubility of solid A at different temperatures.
      Table 1  
      

      Volume of water  added(cm3)	Temperature at which first  crystals appear (oC)	Solubility of solid A (g/100g of water)
      10
      12
      14
      16

      (5 marks)
   2. On the grid provided, plot a graph of the solubility of solid A against temperature.  (3 marks)
   3. Using the graph determine the temperature at which 52g of solid A would dissolve in  100cm³of water. (1 mark) 

Procedure II 

1. Transfer the contents of the boiling tube in procedure I into a 250ml volumetric  flask. Rinse both the boiling tube and the thermometer with distilled water and add  it to the volumetric flask. Add more distilled water to make up to the mark. Transfer  the solution into a 250ml beaker. Label this solution E. Rinse the volumetric flask  with distilled water ready for use in step (ii).
2. Using measuring cylinder, place 25cm³of solution B into a 250ml volumetric flask.  Add about 200cm³of distilled water and shake well. Add more distilled water to  make up to the mark. Label this solution F.
3. Fill the burette with solution E. using a pipette filler, place 25cm³of solution F into  a conical flask. Add 2-3 drops of phenolphthalein indicator and titrate with solution E. record your results in table II. Repeat this procedure two more times to complete  the table 2 below. 
   Table 2 

   	1	2	3
   Final burette reading (cm³)
   Initial burette reading (cm³)
   Volume of Solution E used (cm³)

   (4 marks)
   1. Determine the average volume of solution E used. (1 mark)
   2. Determine the concentration of solution F in moles per litre. (1 mark)
   3. Calculate the number of moles in 25cm³of solution F. (1 mark)
   4. Calculate the moles of alkanoic acid, solution E used (1 mole of acid reacts with  2 moles of base). (1 mark)
   5. Calculate the concentration of solution E in moles per litre. (1 mark)
   6. Determine the relative formula mass of the alkanoic acid, Solid A.  (C =12, H=1, O=16)
       (2 marks)

Question 2

You are provided with solid R. Carry out the tests below. Write your observations and  inferences in the spaces provided. 

Place solid R in a boiling tube, add 10cm³of distilled water and shake well. Use about  2cm³portions for test (i) to (v) below. 

1. Add 3 drops of sodium sulphate solution. 
   

   Observations	Inferences
   (1 mark)	(1 mark)

2. Add sodium hydroxide solution dropwise until in excess. 
   

   Observations	Inferences
   (1 mark)	(1 mark)

3. Add aqueous ammonia dropwise until in excess. 
   

   Observations	Inferences
   (1 mark)	(1 mark)

4. Add 3 drops of barium (II) nitrate solution 
   

   Observations	Inferences
   (1 mark)	(1 mark)

5. Add 3 drops of potasium dichromate(VI) solution 
   

   Observations	Inferences
   (1 mark)	(1 mark)

Question 3

You are provided with an organic substance, solid Q. You are required to carry out the  tests indicated below.  

Place a ALL of solid Q in a boiling tube. Add about 10 cm³of distilled water and shake well. Divide the mixture into four equal portions in test tubes.  

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 three drops of acidified potassium dichromate (VI). 
   

   Observations	Inferences
   (1 mark)	(1 mark)

3. To the third portion, add all the sodium hydrogen carbonate. 
   

   Observations	Inferences
   (1 mark)	(1 mark)

4. Test the pH of the fourth portion using universal indicator solution provided. 
   

   Observations	Inferences
   (1 mark)	(1 mark)

CONFIDENTIAL

INSTRUCTIONS TO SCHOOLS 

In addition to the fittings and apparatus found in a chemistry laboratory, each candidate will require  the following: 

1. Each candidate 
   1. About 50cm³of solution B 
   2. One burette 0 – 50 ml
   3. One pipette 25.0ml and a pipette filler
   4. One Filter funnel
   5. 250ml beaker
   6. 6.2g of Solid A exactly weighed in a stoppered container
   7. Two clean dry 250 ml conical flasks
   8. Five (5) clean and dry test tubes on a test tube rack
   9. One boiling tube
   10. Thermometer (-10^oC to 110^oC)
   11. 0.2g of solid sodium hydrogen carbonate supplied in a stoppered container
   12. About 500cm³of distilled water supplied in a wash bottle
   13. One 250ml volumetric flask  
   14. One 50ml measuring cylinder
   15. Two (2) labels
   16. One metallic spatula
   17. One test tube holder
   18. pH chart
   19. A white tile
   20. About 0.5g of solid R supplied in a stoppered container
   21. About 0.5g of solid Q supplied in a stoppered container 
2. Access to: 
   1. Phenolphthalein indicator supplied with a dropper
   2. Bunsen burner  
   3. 2.0M aqueous ammonia supplied with a dropper
   4. 2.0M sodium hydroxide solution supplied with a dropper
   5. Acidified potasium dichromate (VI) solution supplied with a dropper
   6. Acidified potassium manganate (VII) solution supplied with a dropper 7. 1.0M Sodium sulphate solution supplied with a dropper
   7. 0.5M Barium (II) nitrate solution supplied with a dropper
   8. Universal indicator solution 
3. Preparation of solutions and solids 
   1. Solution B (2.0M Sodium Hydroxide) is prepared by dissolving 80.0g of sodium  hydroxide in 700cm³of distilled water and diluting it to one litre. 
   2. Solid R is Zinc Sulphite 
   3. Solid Q is Maleic acid 
   4. Solid A is Exactly 6.2g oxalic acid 

MARKING SCHEME

Question 1

Procedure I

1.  Table 1
   

   Volume of water  added(cm3)	Temperature at which first  crystals appear (oC)	Solubility of solid A (g/100g of water)
   10	54.0	62.0
   12	50.5	51.7
   14	47.0	44.3
   16	42.0	38.8

2.   
   

Procedure II

Table 2

1. = 12.6 + 12.7 + 12.8
                   3
   = 12.7cm³ 
2. 2 × 25 = M × 250
   M = 0.2M
3. 0.2 × 25 = 0.005
      1000
4. 0.005 = 0.0025
      2
5. 0.0025 × 1000 = 0.19685
     12.7
6. Conc. in g/l = 6.2 × 1000
                             250
                     = 24.8
   RFM =    24.8.   
              0.19685
           = 125.98

Question 2

1.  
   

   Observations	Inferences
   No white ppt       (1 mark)	Ca2+, Pb2+, Ba2+  absent.     (1 mark)

2.  
   

   Observations	Inferences
   White ppt that dissolves in excess (1 mark)	Zn2+ , Al3+ present (1 mark)  Penalize ½mk mfor Pb2+ if mentioned

3.  
   

   Observations	Inferences
   White ppt soluble in excess   (1 mark)	Zn2+ present (1 mark)  Penalize FULLY for any contradicting ion mentioned

4.  
   

   Observations	Inferences
   White ppt     (1 mark)	SO42−, SO32− present       (1 mark)   Penalize ½mk for CO32− if mentioned

5.  
   

   Observations	Inferences
   Orange Cr2O72−  Solution changes to green (1 mark)	SO32− present  (1 mark)  Penalize FULLY for any contradiction

 Question 3

1.  
   

   Observations	Inferences
   Purple KMnO4 changes to colourless/ is decolourised  (1 mark)	present     (1 mark)

2.  
   

   Observations	Inferences
   K2Cr2O7 remains orange (1 mark)	present          or    R−OH absent       (1 mark)

3.  
   

   Observations	Inferences
   Effervescence/ Bubbles/ Fizzling  (1 mark)	R–COOH present accept H+/H3O+ for ½.     (1 mark)

4.  
   

   Observations	Inferences
   pH value 1/2/3  (1 mark)  Value must be specified	strongly acidic (1 mark)