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:
QUESTION |
MAXIMUM SCORE |
CANDIDATE’S SCORE |
1 |
24 |
|
2 |
8 |
|
3 |
8 |
|
Total Score |
40 |
QUESTIONS
- 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:- Standardize solution D with solution B
- Determine the ratio between sodium hydroxide, solution A and the carboxylic acid, solution C
- 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)
I |
II |
III |
|
Final burette reading (cm3) |
|||
Initial burette reading (cm3) |
|||
Volume of solution B used (cm3) |
- Determine the average volume of solution B used. (1mark)
- Calculate the concentration in moles per litre of sodium hydroxide in :
- Solution D (2marks)
- 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)
Volume of solution C, cm3 |
16 |
12 |
8 |
6 |
4 |
2 |
Volume of solution A, cm3 |
4 |
8 |
12 |
14 |
16 |
18 |
Final temperature (ºC) |
||||||
Initial temperature (ºC) |
||||||
Change in temperature, |
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:
- Ratio between the volumes of solution A and C (2marks)
- 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.
- 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)
- 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.
- To about 1cm3 of solution, add 2M sodium hydroxide drop wise until in excess.
Observations
Inferences
(1mark)
(1mark)
- Place 1cm3 of solution in a test – tube and add 2 to 3 drops of 2M sulphuric (VI) acid.
Observations
Inferences
(1mark)
(1mark)
- To about 1cm3 of solution, add 4-5 drops of lead (II) nitrate solution and heat to boiling.
- To about 1cm3 of solution, add 2M sodium hydroxide drop wise until in excess.
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.
- Test the first portion with both blue and red litmus papers
Observations
Inferences
(1mark)
(1mark)
- To the second portion, add three drops of bromine water
Observations
Inferences
(1mark)
(1mark)
- To the third portion, add 2 drops of acidified potassium manganate (VII) and shake well.
Observations
Inferences
(1mark)
(1mark)
- 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:
- Burette (0-50 cm3)
- Filter funnel
- Pipette 25cm3
- One pipette filler
- 3g of solid G
- Two 250ml conical flasks
- About 120ml of solution A
- About 100ml of solution B
- About 60ml of solution C
- About 100ml of solution D
- One 10ml measuring cylinder
- Thermometer (-10 – 110ºC)
- 100ml plastic beaker
- Two boiling tubes
- One test – tube holder
- 2 red and 2 blue litmus papers
- [1]g of solid E
- 5g of solid F
- 6 clean dry test – tubes
- About 500ml distilled water Access to the following:
- 0M sodium hydroxide supplied with a dropper
- 5M Lead (II) nitrate supplied with a dropper
- Bunsen burner
- Phenolphthalein indicator supplied with a dropper
- 2M sulphuric (VI) acid
- Bromine water supplied with a dropper
- Acidified potassium manganate (VII) supplied with a dropper
NOTES AND PREPARATION
- Solution A is made by dissolving 48g of sodium hydroxide in 500cm3 of distilled water and diluting to make one litre.
- Solution B is made by dissolving 12cm3 of concentrated hydrochloric acid in about 600cm3 of distilled water and diluting it to one litre.
- Solution C is prepared by dissolving 76g of oxalic acid in 600cm3 of distilled water and diluting to one litre
- Solution D is prepared by dissolving 4g of sodium hydroxide in 600cm3 of distilled water and diluting to one litre.
- Solid G is NaHCO3
- Solid E is calcium chloride
- Solid F is benzoic acid
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