React, filter, crystallise, dry. Stop before it is dry.
Making crystals of a soluble salt comes up again and again in 0620 Paper 6, as a diagram to finish, a method to describe or a plan to write. Here you warm dilute sulfuric acid, add copper(II) carbonate in excess, filter, heat the filtrate to the crystallisation point and dry the crystals. You also see the titration method for soluble reactants, and why crystals form as a hot solution cools.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge IGCSE Chemistry 0620 Paper 6 (Alternative to Practical). It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 0620/61 May/June 2023, (Question 4, planning: pure, dry crystals from an insoluble base) · official past papers
Practise next: 0620/61 May/June 2025, (Question 1, a soluble salt by titration, then crystals) · official past papers
Practise next: 0620/62 February/March 2023, (Question 2, solubility of a salt at different temperatures) · official past papers
Examiner reports used: 0620 March 2023, June 2023, November 2023, March 2024, June 2024, November 2024 and June 2025 (Paper 6).
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What a full-mark diagram shows
React
Warm the dilute acid in a beaker and add the insoluble base or carbonate a spatula at a time, stirring with a glass rod, until no more reacts and some solid is left: it is in excess.
Filter
A filter funnel lined with filter paper. The residue is the excess solid; the filtrate is the salt solution.
Crystallise
Heat the filtrate in an evaporating basin until crystals form on a cold glass rod. Stop there: do not heat to dryness.
Cool and dry
Leave the saturated solution to cool so crystals form, filter them off and dry them between filter papers.
Habits the examiner reports keep asking for
Say what each item is for. A list of apparatus at the start of a plan gains no credit.
Say “in excess” and why: so that all the acid reacts.
Use the right names: funnel (not “filter”), glass rod (not “stirrer”), evaporating basin.
Give a method, not one word. “Heat to the crystallisation point” and “dry between filter papers”, not just “evaporate” or “dry it”.
Read and record carefully: thermometers to the nearest half division, all values to the same number of decimal places, and a smooth curve when the points curve.