# A student heats a sample of candle wax and records the temperature at which it melts. He then heats a sample of naphthalene and records its melting point. Explain how the melting point data for each substance shows whether it is pure or impure.

> Eduqas GCSE Chemistry — 1.1 The nature of substances and chemical reactions · Explain · 4 marks

> Candle wax melts gradually between 46 °C and 68 °C. Naphthalene melts sharply at 80 °C.

## Mark scheme (4 marks)

1. A pure substance has a sharp/specific melting point (melts at one exact temperature)
2. Naphthalene melts at one fixed temperature (80 °C), so it is a pure substance
3. A mixture/impure substance melts over a range of temperatures
4. Candle wax melts over a range of temperatures (46–68 °C), so it is impure/a mixture

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE 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-student-heats-a-sample-of-94005b00) · Published by Druglandscape Ltd.