## Questions

Instructions to candidates

• Answer ALL questions in this paper.
• All workings must be shown clearly.
• Mathematical tables and non-programmable electronic calculators may be used where necessary

1. You are provided with:
• Solid A
• 2.0M hydrochloric acid, solution B.
• 0.10M sodium hydroxide

You are required to determine the enthalpy change ∆H, for the reaction between solid A and 1 mole of hydrochloric acid.
• Procedure 1.
• Using a burette, place 20.0cm3 of hydrochloric acid solution B in a 100 ml beaker.
• Measure the temperature of the solution after every half minute and record the values in table 1. At exactly 2 ½ minute, add all of solid A to the acid, stir the mixture gently with the thermometer.
• Measure and record the values in table 1. (Retain the mixture for use in procedure II).

Table 1. (4 marks)
 Time (min) 0 1 1½ 2 2½ 3 3½ 4 4½ 5 Temperature (°C) x
1. Plot a graph of temperature (Y – axis) against time on the grid provided. (3 marks)
2. Using the graph, determine the temperature change ∆T (1 mark)
3. Calculate the heat change for the reaction (Assume that specific heat capacity of the mixture is 4.2 j/g/k and the density of the mixture is 1g/cm 3 (2 marks)
• Procedure II
• Rinse the burette thoroughly and fill it with sodium hydroxide. Transfer all the contents of the 100ml beaker used in procedure I into a 250ml volumetric flask.
• Add distilled water to make it to the mark. Label this solution C.
• Using a pipette and pipette filer, place 25 cm 3 of solution C into a 250ml conical flask.
• Add two or three drops of phenolphthalein indicator and titrate against sodium hydroxide. Record your results in table 2. Repeat titration two more times and complete (4 marks)
Table 2.
 Test Final burette reading (cm3 ) Initial burette reading (cm3 ) Titre (cm3 )

Calculate:
1. The average volume of sodium hydroxide used. (1 mark)
2. The number of moles of
1. Sodium hydroxide used. (1 mark)
2. Hydrochloric acid in 25cm3 of solution C. (1 mark)
3. Hydrochloric acid in 250ml of solution C. (1 mark)
4. Hydrochloric acid in 20.0cm3 of solution B. (1 mark)
5. Hydrochloric acid that reacted with solid A. (1 mark)
3. Calculate the enthalpy of reaction between A and one mole of hydrochloric acid (show the sign of ∆H) (2 marks)
2. You are provided with solid E carry out the tests below and record your observations and inferences in the spaces provided.
1. Place about one third of solid E in a clean dry test-tube and heat it strongly.
 Observation Inference
2. Place the remaining solid E in a boiling tube. Add about 10cm 3 of distilled water; shake the mixture thoroughly for about one minute. Filter and divide the filtrate into four portions.
 Observation Inference
3. To the first portion, add two drops of phenolphthalein indicator.
 Observation Inference
4. To the second portion add 2cm3 of dilute hydrochloric acid
 Observation Inference
5. To the third proportion, add 5cm3 of aqueous sodium sulphate.
 Observation Inference
6. To the fourth portion, add dilute sodium hydroxide dropwise until excess.
 Observation Inference
3. You are provided with liquid F. Carry out the following tests and record your observations and interferences in the spaces provided.
1. Place five drops of liquid F in a clean dry watch glass and ignite it.
 Observation Inference
2. Place about 2cm 3 of liquid F in a clean dry test – tube, add all the sodium hydrogen carbonate provided.
 Observation Inference
3. Place about 2cm 3 of liquid F in a test – tube add about 1 cm 3 of acidified potassium dichromate (VI) and warm the mixture.
 Observation Inference

## Confidential

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

1. Each candidate
1. About 25cm3 of solution B
2. About 80cm3 of 0.1M sodium hydroxide solution
3. One burette 0 – 50 ml
4. 1.3g of solid A accurately weighed supplied in a stoppered container
5. One pipette 25.0ml and a pipette filler
6. Thermometer (-10°C to 110°C)
7. One Filter funnel
8. 100ml plastic beaker
9. Two clean dry 250 ml conical flasks
10. Six (6) clean and dry test tubes on a test tube rack
11. One boiling tube
12. Watch glass
13. 1 label sticker
14. 0.3g of solid sodium hydrogen carbonate
15. About 500cm3 of distilled water supplied in a wash bottle
17. 2 filter papers (125mm Whatman no. 1)
18. One 10ml measuring cylinder
19. One metallic spatula
20. One test tube holder
21. One stopwatch
22. A white tile
23. About 2.0g of solid E supplied in a stoppered container
24. About 5ml of liquid F supplied in a stoppered container
1. Phenolphthalein indicator supplied with a dropper
2. Source of heat
3. 0.2M aqueous sodium sulphate supplied with a dropper
4. 0.2M dilute hydrochloric acid
5. 0.2M sodium hydroxide solution supplied with a dropper
6. Acidified potassium dichromate (VI) solution
3. Preparation of solutions and solids
1. Solution B is prepared by accurately adding 172cm3of concentrated hydrochloric acid (density 1.18gcm3) to about 500cm3 of distilled water and diluting with distilled water to make one litre solution.
2. Sodium hydroxide is prepared by dissolving 4.0g of sodium hydroxide in 700cm3 of distilled water and diluting it to one litre.
3. Acidified potassium dichromate (VI) is prepared by dissolving 30g of potassium dichromate (VI) in 400cm3 of 2M sulphuric (VI) acid and diluting with distilled water to 1 litre.
4. Solid E is a Barium hydroxide
5. Solid A is sodium hydrogen carbonate
6. Solid F is absolute ethanol

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