233/3 · CHEMISTRY (Practical) · Paper 3 · Dec. 2022 · 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; use this time to read the question paper and check the materials and apparatus. All working must be clearly shown where necessary. Mathematical tables and silent electronic calculators may be used.
Question 1 (20 marks)
(a) You are provided with: solution A — indicator solution; solution B — 0.05 M compound B; solution C1 — hydrochloric acid to be used in questions 1(a) and 1(b). You are required to determine the concentration in moles per litre of hydrochloric acid in solution C1.
Procedure I (a)
(i) Place two test tubes in a test tube rack. To the first test tube, place about 2 cm³ of solution B. To the second test tube, place about 2 cm³ of solution C1.
(ii) Add 2 drops of indicator solution A to each of the test tubes, shake and note the colour of each solution. Record the colours in Table 1. (1 mark)
| Solution | Colour |
|---|---|
| Solution B + indicator solution A | |
| Solution C1 + indicator solution A |
Complete the following statement: In the titration of solution B (in a conical flask) with hydrochloric acid using indicator solution A, the colour change at the end point is from ……… to ……… (1 mark)
Procedure II (a)
(i) Using a pipette and pipette filler, pipette 25.0 cm³ of solution C1 into a 250 ml volumetric flask. Add distilled water to the mark. Label this as solution C2.
(ii) Fill a burette with solution C2.
(iii) Using a clean pipette and pipette filler, place 25.0 cm³ of solution B in a 250 ml conical flask.
(iv) Titrate solution B with solution C2 using 3 drops of indicator solution A. Record the results in Table 2. (4 marks)
| I | II | III | |
|---|---|---|---|
| Final burette reading | |||
| Initial burette reading | |||
| Volume of solution C2 used (cm³) |
Calculate the: (i) average volume of solution C2 used; (1 mark) (ii) number of moles of compound B used; (1 mark) (iii) number of moles of hydrochloric acid used (1 mole of compound B reacts with 2 moles of hydrochloric acid); (1 mark) (iv) concentration in moles per litre of hydrochloric acid in solution C2; (1 mark) (v) concentration in moles per litre of hydrochloric acid in solution C1. (1 mark)
(b) You are provided with two portions of solid D, sodium hydrogen carbonate, each weighing 2.5 g. You are required to determine the heat of reaction of hydrochloric acid with aqueous sodium hydrogen carbonate.
Procedure I (b)
(i) Using a 100 ml measuring cylinder, measure 30 cm³ of distilled water and place it in a 100 ml plastic beaker.
(ii) Measure the temperature of the distilled water and record it in Table 3.
(iii) Add one of the portions of solid D to the water. Stir with the thermometer and measure the minimum temperature reached. Record the reading in Table 3. (1½ marks)
| Final temperature of the solution (°C) | |
| Initial temperature of water (°C) | |
| Temperature change (°C) |
Calculate the: (i) heat change of the solution (specific heat capacity of solution = 4.2 J g⁻¹ K⁻¹; density of solution = 1.00 g cm⁻³); (1 mark) (ii) number of moles of sodium hydrogen carbonate, solid D, used (relative formula mass = 84); (1 mark) (iii) heat change, ΔH₁, in kJ mol⁻¹ of sodium hydrogen carbonate. (1 mark)
Procedure II (b)
(i) Clean the 100 ml plastic beaker.
(ii) Repeat procedure I (b) using the second portion of solid D and 30 cm³ of solution C1 instead of 30 cm³ of distilled water.
(iii) Record the results in Table 4. (1½ marks)
| Final temperature of solution (°C) | |
| Initial temperature of solution C1 (°C) | |
| Temperature change (°C) |
Calculate the: (i) heat change of the solution; (1 mark) (ii) heat change, ΔH₂, in kJ mol⁻¹ of sodium hydrogen carbonate; (1 mark) (iii) heat change, ΔH₃ = ΔH₂ − ΔH₁, for the reaction of hydrochloric acid with one mole of aqueous sodium hydrogen carbonate. (1 mark)
Question 2 (8 marks)
You are provided with an organic compound, solid M. Carry out the following tests and record the observations and inferences in the spaces provided.
(a) Place about one-fifth of solid M on a metallic spatula and burn it using a Bunsen burner flame. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
(b) Place the remaining amount of solid M in a boiling tube. Add about 15 cm³ of distilled water and shake to dissolve. Use about 2 cm³ portions of the solution, in a test tube, for each of the following tests.
(i) To the first portion, add 3 drops of acidified potassium dichromate(VI). Warm the mixture. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
(ii) To the second portion, add 3 drops of bromine water. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
(iii) To the third portion, add all the solid sodium carbonate provided. Test any gases produced with a burning splint. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
Question 3 (12 marks)
You are provided with solution N. Carry out the following tests and record the observations and inferences in the spaces provided. Use about 2 cm³ portions, in a test tube, for each of the tests.
(a) To the first portion, add aqueous sodium hydroxide dropwise until in excess. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
(b) Warm the second portion and then add aqueous ammonia dropwise until in excess. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
(c) To the third portion, add 3 drops of aqueous barium nitrate. Shake and then add about 1 cm³ of dilute nitric(V) acid. (2 marks, 1 mark)
| Observations | Inferences |
|---|---|
(d) Place about 1 cm³ of aqueous sodium hydroxide in a test tube, then add the fourth portion of solution N.
(i) Heat the mixture and test any gases produced with red litmus paper. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
(ii) Rewarm the mixture obtained in (d)(i), then add the piece of folded aluminium foil provided. Test any gases produced with red litmus paper. (1 mark, 1 mark)
| Observations | Inferences |
|---|---|
Identify a cation and two anions in solution N. Cation: ……… (½ mark) Anions: ……… (½ mark)