# A chemist is testing two liquid samples, X and Y, to find out whether each one is a pure substance or a mixture. The chemist heats both samples carefully and records the temperature at which each one boils. Sample X boils at a single, sharp temperature of 78 °C. Sample Y boils over a range of temperatures between 82 °C and 97 °C. Explain what these boiling point results tell the chemist about samples X and Y, and state one further test the chemist could carry out to confirm these conclusions.

> Eduqas A-Level Chemistry — 1.4 States of matter · Explain · 5 marks

## Mark scheme (5 marks)

1. Sample X is a pure substance
2. Because pure substances boil at a single, sharp (specific) temperature
3. Sample Y is a mixture
4. Because mixtures boil over a range of temperatures
5. Carry out paper chromatography (or melting point determination) — a pure substance produces a single spot in all solvents / has a sharp melting point, whereas a mixture produces more than one spot / melts over a range

## Key terms

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

## 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-chemist-is-testing-two-liquid-17987905) · Published by Druglandscape Ltd.