A student uses simple distillation to separate ethanol from a mixture of ethanol and water. Explain why simple distillation is able to separate these two liquids, and describe what happens to the mixture during the process.

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

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

Model answer (4 marks)

Ethanol and water have different boiling points.
Ethanol has a lower boiling point (78 °C) than water (100 °C), so it evaporates first.
The ethanol vapour is carried into a condenser where it is cooled and condenses back into liquid, which is collected.
As distillation proceeds the remaining liquid becomes richer in water and the amount of ethanol in the mixture decreases.

Examiner tips

  • State the boiling‑point difference first. Explain the sequence: evaporation, condensation, collection. Mention the change in composition of the residue.
  • common_mistakes
  • :
  • Saying both liquids evaporate at the same time. Forgetting to note that the residue becomes water‑rich.

Mark scheme (4 marks)

  1. Ethanol and water have different boiling points
  2. Ethanol has a lower boiling point (than water) so it evaporates first / the liquid with the lowest boiling point evaporates first
  3. The ethanol vapour is cooled and condensed (in a condenser) and collected as a liquid
  4. As distillation continues, the remaining solution becomes more concentrated in water / the amount of ethanol in the mixture decreases

Key terms in this question

simple distillation

Related

More Rate of chemical change questions

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