233/3 · CHEMISTRY · Paper 3 (Practical) · Nov. 2024 · 2¼ hours
Instructions: Answer all the questions in the spaces provided. 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 chemicals and apparatus that you may need. All working must be clearly shown where necessary. KNEC mathematical tables and silent electronic calculators may be used.
The source file for this paper is retyped and differs from the usual KNEC layout; treat its wording with care.
Question 1 (26 marks)
You are provided with: aqueous sodium hydroxide solution A; 0.1 M HCl solution B; solid C; 2.0 M HCl solution D.
You are required to determine: (i) the concentration of sodium hydroxide solution A; (ii) the molar enthalpy of reaction between solid C and solution D.
Procedure 1
Fill the burette with solution A, aqueous sodium hydroxide. Using a pipette and pipette filler, place 25.0 cm³ of solution B (HCl) into a clean conical flask. Add 3 drops of phenolphthalein indicator and titrate solution B with A from the burette. Record your results in Table I below. Repeat the titration 2 more times to complete the table.
| I | II | III | |
|---|---|---|---|
| Final burette reading (cm³) | |||
| Initial burette reading (cm³) | |||
| Volume of solution A (cm³) |
(4 marks)
I. Determine:
(a) the average volume of solution A used; (1 mark)
(b) the number of moles of hydrochloric acid solution B used; (1 mark)
(c) the number of moles of sodium hydroxide solution A used; (1 mark)
(d) the concentration of aqueous sodium hydroxide solution A. (1 mark)
Procedure 2
Using a 100 ml measuring cylinder, place 50 cm³ of hydrochloric acid solution D into a 100 ml plastic beaker. Stir gently with the thermometer and note its temperature in Table II below. Start a stop watch and note the temperature of solution D in the beaker after every 30 seconds. At 2 minutes add all of solid C at once and continue stirring the mixture with the thermometer and record the temperature of the mixture after every half minute up to the 7th minute. (Preserve the solution obtained for Procedure 3.)
| Time (minutes) | 0 | 1 | 1½ | 2 | 2½ | 3 | 3½ | 4 | 4½ | 5 | 5½ | 6 | 6½ | 7 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temperature (°C) |
(4 marks)
II. (a) Plot a graph of temperature (y-axis) against time. (3 marks)
(b) From the graph, determine the highest change in temperature.
(c) Calculate the enthalpy change for the reaction. (Given that c = 4.2 kJ kg⁻¹ K⁻¹; density of solution = 1 g cm⁻³)
Procedure 3
Transfer all the contents of the 100 ml beaker into a 250 ml volumetric flask. Add distilled water to make up to the mark. Label the resulting solution as solution E. Refill the burette with solution A, aqueous sodium hydroxide. Using a pipette and pipette filler, place 25.0 cm³ of E into a conical flask. Add 3 drops of phenolphthalein indicator. Titrate solution E with solution A until there is a permanent colour change. Record your results in Table III below. Repeat the titration two more times and complete Table III.
| I | II | III | |
|---|---|---|---|
| Final burette reading (cm³) | |||
| Initial burette reading (cm³) | |||
| Volume of solution A (cm³) |
(4 marks)
I. Determine:
(a) the average volume of sodium hydroxide solution A used; (1 mark)
(b) the number of moles of sodium hydroxide solution A used; (1 mark)
(c) Calculate the:
(i) number of moles of hydrochloric acid present in solution E used; (1 mark)
(ii) number of moles of hydrochloric acid present in 250 cm³ of solution E; (1 mark)
(iii) number of moles of hydrochloric acid present in solution D; (1 mark)
(iv) number of moles of hydrochloric acid solution D that reacted with solid C; (1 mark)
(v) molar enthalpy change for the reaction between solution D and solid C. (1 mark)
Question 2 (12 marks)
You are provided with solid F. Carry out the tests below and record your observations and inferences in the spaces provided.
(a) Place half of solid F into a clean dry test tube. Heat gently and then strongly. Test for any gas using litmus papers. (2 marks)
| Observations | Inferences |
|---|---|
(b) Place the other half of solid F in a boiling tube, add 10 cm³ of distilled water and shake to dissolve. Divide the resulting solution into 4 portions. (2 marks)
| Observations | Inferences |
|---|---|
(c) (i) To the 1st portion add sodium hydroxide dropwise until in excess. (2 marks)
| Observations | Inferences |
|---|---|
(ii) To the 2nd portion add aqueous ammonia dropwise until in excess. (2 marks)
| Observations | Inferences |
|---|---|
(iii) To the 3rd portion add 3 drops of sodium chloride solution. (2 marks)
| Observations | Inferences |
|---|---|
(iv) To the 4th portion add aqueous barium nitrate solution followed by dilute nitric(V) acid. (2 marks)
| Observations | Inferences |
|---|---|
Question 3 (12 marks)
You are provided with solid G. Carry out the tests below and record your observations and inferences in the spaces provided.
(a) Place half of solid G in a metallic spatula and burn in a non-luminous flame. (2 marks)
| Observations | Inferences |
|---|---|
(b) Place the other half in a boiling tube and add 10 cm³ of distilled water and shake. Divide the resulting solution into 4 portions. (2 marks)
| Observations | Inferences |
|---|---|
(c) (i) To the 1st portion add sodium hydrogen carbonate. (2 marks)
| Observations | Inferences |
|---|---|
(ii) To the 2nd portion add acidified potassium dichromate(VI). (2 marks)
| Observations | Inferences |
|---|---|
(iii) To the 3rd portion add bromine water. (2 marks)
| Observations | Inferences |
|---|---|
(iv) To the 4th portion dip the litmus paper provided. (2 marks)
| Observations | Inferences |
|---|---|