# A technician is testing two white solid substances, substance A and substance B, to find out whether each one is a pure substance or a mixture. The technician heats both substances slowly and records the temperature at which each one melts. Substance A melts completely at exactly 58 °C. Substance B begins to soften at 52 °C and is fully melted by 61 °C. Explain what the melting point data tell the technician about the purity of substance A and substance B.

> Eduqas A-Level Chemistry — 1.1 Atoms, molecules and stoichiometry · Explain · 5 marks

## Mark scheme (5 marks)

1. Substance A has a sharp melting point (melts at one specific temperature / melts at exactly 58 °C)
2. A sharp melting point indicates substance A is a pure substance (contains only one element or compound)
3. Substance B melts over a range of temperatures (begins to soften at 52 °C and is not fully melted until 61 °C / does not have a sharp melting point)
4. Melting over a range of temperatures indicates substance B is a mixture
5. In a mixture, the substances are not chemically bonded/combined together, so each component affects the melting behaviour, causing the range

## Key terms

- [pure substance](https://www.gradenine.co.uk/glossary/pure-substance)
- [mixture](https://www.gradenine.co.uk/glossary/mixture)
- [melting point data](https://www.gradenine.co.uk/glossary/melting-point-data)

## Related

- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-technician-is-testing-two-white-767e8c33) · Published by Druglandscape Ltd.