O Level Chemistry 5070 Paper 42, Oct/Nov 2024

The student makes aqueous copper(II) sulfate by reacting a dilute acid with excess copper(II) oxide. Name the acid.

Fig. 1.1 shows the apparatus the student uses to crystallise the aqueous copper(II) sulfate. Name apparatus X.

Describe how the student decides when to stop heating the aqueous copper(II) sulfate.

Suggest why apparatus X is heated with a water bath and not heated directly using the Bunsen burner.

Describe the final step needed to produce pure hydrated copper(II) sulfate crystals.

Fig. 2.1 shows the burette readings for two of the titrations. Record the burette readings in Table 2.1. Complete Table 2.1.

Tick (✓) the two best titration results in Table 2.1.

Use the ticked (✓) titration results in Table 2.1 to calculate the average volume of $\mathrm{H}\mathrm{C}\mathrm{l}(\mathrm{a}\mathrm{q})$ needed to neutralise $25.0{\mathrm{c}\mathrm{m}}^3$ of the aqueous sodium carbonate.

Use your answer from (c) to calculate the number of moles of $\mathrm{H}\mathrm{C}\mathrm{l}$ in the average volume of $\mathrm{H}\mathrm{C}\mathrm{l}(\mathrm{a}\mathrm{q})$ needed to neutralise $25.0{\mathrm{c}\mathrm{m}}^3$ of the aqueous sodium carbonate.

The equation for the reaction between hydrochloric acid and sodium carbonate is: $$2\mathrm{H}\mathrm{C}\mathrm{l}+{\mathrm{N}\mathrm{a}}_2{\mathrm{C}\mathrm{O}}_3\to 2\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{C}\mathrm{O}}_2$$ Use your answer from (d) to calculate the concentration of the aqueous sodium carbonate. Give your answer to three significant figures.

The student is provided with $150{\mathrm{c}\mathrm{m}}^3$ of the aqueous sodium carbonate. Use your answer to (e) to calculate the mass of ${\mathrm{N}\mathrm{a}}_2{\mathrm{C}\mathrm{O}}_3$ in $150{\mathrm{c}\mathrm{m}}^3$ of this solution. [$A_r$: $\mathrm{C},12$; $\mathrm{O},16$; $\mathrm{N}\mathrm{a},23$]

State why the conical flask is swirled while $\mathrm{H}\mathrm{C}\mathrm{l}(\mathrm{a}\mathrm{q})$ is added from the burette.

State why the $\mathrm{H}\mathrm{C}\mathrm{l}(\mathrm{a}\mathrm{q})$ is added drop by drop near the end-point.

Solution P is colourless and contains sodium ions. Describe how to do a flame test on solution P to confirm the identity of this cation.

Solution P contains an anion composed of nitrogen and oxygen. Describe a test to identify the anion in solution P. test .................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... observations ...................................................................................................................... ........................................................................................................................................... identity of anion .................................................................................................................

The tests the student does on solution Q are shown in Table 3.1. Some of the observations for these tests are also shown. Identify the cation in solution Q using the observations from tests 1 and 2.

Test 3 is incomplete. Describe what else must be done in test 3 to ensure that the white precipitate observed leads to a valid conclusion about the anion in solution Q.

The student completes test 3 correctly. The observation remains the same. Identify an anion in solution Q.

The ion identified in (iii) is the only anion in solution Q. Describe the expected observation from test 4.

Solution Q is acidic. Describe the observation when solution Q is added to sodium carbonate.