# A food scientist is checking whether a red food colouring used in a new drink is a pure substance or a mixture. The scientist carries out paper chromatography using water as the solvent. After the experiment, the scientist observes that the red food colouring has produced three separate spots on the chromatography paper. Explain what this result tells the scientist about the red food colouring, and describe what result would be expected if the food colouring were a pure substance.

> WJEC A-Level Chemistry (Wales) — 1.4 States of matter · Explain · 5 marks

## Mark scheme (5 marks)

1. The red food colouring is a mixture (not a pure substance)
2. Because it contains more than one compound / the different compounds separate into different spots
3. The substances separate because they have different solubilities in the mobile phase (water / solvent)
4. A pure substance would produce only a single spot on the chromatography paper
5. A pure substance produces a single spot in all solvents / the single spot indicates only one compound is present

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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-food-scientist-is-checking-whether-bec85fa6) · Published by Druglandscape Ltd.