A student wants to separate a mixture of two liquids that are miscible with each other and have different boiling points. Describe how the student could use simple distillation to obtain a pure sample of the liquid with the lower boiling point.

Edexcel GCSE Chemistry (1CH0) — 1.2 Methods of separating and purifying substances · Describe · 4 marks · View as Markdown

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

Two miscible liquids, liquid A (boiling point 78 °C) and liquid B (boiling point 100 °C), are mixed together.

Model answer (4 marks)

Heat the mixture until it boils at 78 °C, the boiling point of liquid A. The vapour of liquid A rises and enters a condenser. The condenser cools the vapour so it condenses back into a liquid. The condensed liquid is collected in a separate flask, leaving liquid B behind in the original flask.

Examiner tips

  • Use the word ‘boils’ to show the mixture reaches 78 °C
  • Mention the condenser and that it cools the vapour
  • State that the condensed liquid is collected separately
  • Show that liquid B remains in the original flask

Common mistakes

  • Not specifying the boiling point of liquid A
  • Omitting the condenser or the cooling step
  • Failing to note that liquid B stays in the original flask

Mark scheme (4 marks)

  1. The mixture is heated in a flask until it boils / until it reaches the boiling point of liquid A
  2. The vapour (of liquid A) rises and passes into a condenser / cooled tube
  3. The condenser cools the vapour so that it condenses back into a liquid
  4. The liquid is collected in a separate container / flask, leaving liquid B behind in the original flask

Key terms in this question

simple distillation · miscible · boiling point

Related

More Methods of separating and purifying substances questions

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