Chemistry Paper 3 Questions and Confidential - Mumias West Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES:

•  You are not allowed to start working with the apparatus for the first 15 minutes of the 2 1/4 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 needed.
• Mathematical tables and electronic calculators may be used for calculations
• All workings must be clearly shown where necessary

For Examiner’s Use only:

QUESTIONS

1. You are provided with:
   Sodium hydroxide labeled solution A
   0.128M hydrochloric acid labeled solution B
   Carboxylic acid labeled solution C
   Solution D prepared by diluting 25cm³ of solution A with distilled water to 150cm³ of solution
   You are required to:
   1. Standardize solution D with solution B
   2. Determine the ratio between sodium hydroxide, solution A and the carboxylic acid, solution C
   3. Determine the concentration of C in moles per litre

Procedure 1
Fill the burette with solution B. Pipette 25cm3 of solution D into 250cm3 conical flask. Add 2 drops of phenolphthalein indicator and titrate with solution B. Record your results in table 1 below. Repeat the titration two more times and complete the table.
Table 1 (4marks)

1. Determine the average volume of solution B used. (1mark)
2. Calculate the concentration in moles per litre of sodium hydroxide in :
   1. Solution D (2marks)
   2. Solution A (2marks)

PROCEDURE 2
Using a clean burette, place 16cm³ of solution C into a boiling tube. Take the initial temperature of the solution in the boiling tube and record it in the table 2. Using a clean measuring cylinder, measure 4cm³ of solution A into 100cm³ beaker and add it to solution C in the boiling tube. Stir the mixture immediately with the thermometer and record in Table 2 the maximum (final) temperature reached. Repeat the experiment with the other set volumes of solution C and A in Table 2 and complete it. Rinse the thermometer and the boiling tube with distilled water after each experiment.
Table 2 (6Marks)

c) On the grid provided, plot a graph of change in temperature (vertical axes) against the volume of sodium hydroxide, solution A

d) From the graph, determine the volume of sodium hydroxide solution A required to neutralize the carboxylic acid (1mark)
e) Calculate the volume of carboxylic acid, solution C used for neutralization (1mark)
f) Calculate the:

1. Ratio between the volumes of solution A and C (2marks)
2. Concentration in moles per litre of carboxylic acid, solution C (Assume the volume ratio is the same as the mole ratio) (2marks)

2. You are provided with solid E. Carry out the tests below and record your observations and inferences in the spaces provided.

1. Divide E into halves. Place one half of solid E in a clean dry test-tube. Heat it gently then strongly.
   

   Observations	Inferences
   (1mark)	(1mark)

2. Place the other half of soli E in a boiling tube. Add about 10cm₃ of distilled water and shake well until all the solid dissolves.
   1. To about 1cm₃ of solution, add 2M sodium hydroxide drop wise until in excess.
      

      Observations	Inferences
      (1mark)	(1mark)

   2. Place 1cm₃ of solution in a test – tube and add 2 to 3 drops of 2M sulphuric (VI) acid.
      

      Observations	Inferences
      (1mark)	(1mark)

   3. To about 1cm₃ of solution, add 4-5 drops of lead (II) nitrate solution and heat to boiling.

 3. You are provided with solid F. Carry out the tests below and record your observations and inferences in the spaces provided.
Place all of solid F into a boiling tube. Add about 10cm3 of distilled water and shake well. Use 2cm₃ portion of the mixture for the following tests.

1. Test the first portion with both blue and red litmus papers
   

   Observations	Inferences
   (1mark)	(1mark)

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

   Observations	Inferences
   (1mark)	(1mark)

3. To the third portion, add 2 drops of acidified potassium manganate (VII) and shake well.
   

   Observations	Inferences
   (1mark)	(1mark)

4. Warm the fourth portion slightly and add a little solid G, sodium hydrogen carbonate.
   

   Observations	Inferences
   (1mark)	(1mark)

CONFIDENTIAL

In addition to the fittings and chemicals found in the Chemistry laboratory, each candidate will require the following:

1. Burette (0-50 cm³)
2. Filter funnel
3. Pipette 25cm³
4. One pipette filler
5. 3g of solid G
6. Two 250ml conical flasks
7. About 120ml of solution A
8. About 100ml of solution B
9. About 60ml of solution C
10. About 100ml of solution D
11. One 10ml measuring cylinder
12. Thermometer (-10 – 110ºC)
13. 100ml plastic beaker
14. Two boiling tubes
15. One test – tube holder
16. 2 red and 2 blue litmus papers
17. ^[1]g of solid E
18. 5g of solid F
19. 6 clean dry test – tubes
20. About 500ml distilled water Access to the following:
    1. 0M sodium hydroxide supplied with a dropper
    2. 5M Lead (II) nitrate supplied with a dropper
    3. Bunsen burner
    4. Phenolphthalein indicator supplied with a dropper
    5. 2M sulphuric (VI) acid
    6. Bromine water supplied with a dropper
    7. Acidified potassium manganate (VII) supplied with a dropper

NOTES AND PREPARATION

1. Solution A is made by dissolving 48g of sodium hydroxide in 500cm³ of distilled water and diluting to make one litre.
2. Solution B is made by dissolving 12cm³ of concentrated hydrochloric acid in about 600cm³ of distilled water and diluting it to one litre.
3. Solution C is prepared by dissolving 76g of oxalic acid in 600cm³ of distilled water and diluting to one litre
4. Solution D is prepared by dissolving 4g of sodium hydroxide in 600cm³ of distilled water and diluting to one litre.
5. Solid G is NaHCO₃
6. Solid E is calcium chloride 
7. Solid F is benzoic acid