A student carries out crystallisation to obtain a sample of copper sulfate crystals from a copper sulfate solution. Describe the steps the student should follow to carry out this process.

Eduqas GCSE Chemistry — 1.5 Rate of chemical change · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

1. Heat the copper sulfate solution in an open container to evaporate water and concentrate the solution.
2. Allow the hot solution to cool slowly until it becomes saturated.
3. As the solution cools, copper sulfate crystals nucleate and grow.
4. Filter the crystals from the remaining liquid, then dry the crystals to obtain a pure sample.

Examiner tips

  • Use the word ‘heat’ and ‘cool’ to show the sequence; mention evaporation and saturation. Show that filtration is used to separate crystals from liquid. Include drying as the final step to obtain a dry product.

Common mistakes

  • Omitting the cooling step or describing it as rapid. Failing to mention filtration or using a vague term like ‘separate’. Leaving out the drying step, leaving crystals wet.

Mark scheme (4 marks)

  1. Heat / warm the copper sulfate solution in an open container to allow the solvent (water) to evaporate
  2. Leave the solution to cool / allow the saturated solution to cool slowly
  3. Crystals form / grow as the solution cools
  4. Filter the crystals from the solution / collect the crystals by filtration, then allow them to dry

Key terms in this question

crystallisation

Related

More Rate of chemical change questions

▶ Try answering this question with AI marking (free) →