A pharmaceutical company produces two batches of a painkiller. Batch 1 is described as a pure substance and Batch 2 is described as a mixture. Explain how melting point data could be used to distinguish between the two batches, and what the results would show about the purity of each batch.

WJEC GCSE Chemistry (Wales) — 1.2 Atomic structure and the periodic table · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

A pure substance has a sharp, specific melting point.
A mixture melts over a range of temperatures.
Batch 1 would give a single, sharp melting point, showing it is pure.
Batch 2 would melt over a temperature range, showing it is impure.

Examiner tips

  • Use the word "sharp" for a pure substance and "range" for a mixture.
  • Mention that a single melting point confirms purity, while a range indicates impurities.

Common mistakes

  • Confusing a single melting point with a range, or vice‑versa.
  • Failing to link the melting point behaviour to the purity of each batch.

Mark scheme (4 marks)

  1. A pure substance has a sharp (specific/precise) melting point
  2. A mixture melts over a range of temperatures
  3. Batch 1 (the pure substance) would produce a sharp/single melting point, confirming it is pure
  4. Batch 2 (the mixture) would melt over a range of temperatures, confirming it is impure

Key terms in this question

pure substance · mixture · melting point data

Related

More Atomic structure and the periodic table questions

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