Copper sulfate can be made by reacting copper oxide with dilute sulfuric acid. Describe how a pure, dry sample of copper sulfate crystals could be obtained from this reaction, starting with excess copper oxide powder and dilute sulfuric acid.

Eduqas GCSE Chemistry — 2.2 Acids, bases and salts · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Add excess copper oxide powder to dilute sulphuric acid and heat the mixture to ensure the reaction goes to completion.
Filter the hot mixture to remove the unreacted copper oxide.
Evaporate the filtrate by gentle heating to concentrate the copper(II) sulphate solution.
Cool the concentrated solution; copper(II) sulphate crystals will precipitate.
Collect the crystals by filtration and dry them in a warm oven or on filter paper to obtain a pure, dry sample.

Examiner tips

  • Use the word "add" and "heat" to show the reaction step. Show the sequence: filter → evaporate → cool → dry. Mention that excess copper oxide is removed by filtration. Use UK spelling (sulphuric).

Common mistakes

  • Forgetting to heat the mixture. Not specifying that the crystals are dried after filtration. Using the wrong order of steps (e.g. cooling before evaporation).

Mark scheme (4 marks)

  1. Add excess copper oxide to the dilute sulfuric acid (and warm/heat the mixture)
  2. Filter the mixture to remove the excess unreacted copper oxide
  3. Evaporate (heat) the filtrate / copper sulfate solution to concentrate it / reduce the volume of water
  4. Allow the solution to cool so that copper sulfate crystals form, then dry the crystals (e.g. with filter paper / in a warm oven)

Key terms in this question

excess

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