# A food colouring manufacturer claims that one of its red dyes is a pure substance. A technician carries out paper chromatography on the red dye using two different solvents. In both solvents, the red dye produces three separate spots on the paper. Explain what these results tell the technician about the red dye, and describe what result would be expected if the dye were a pure substance.

> WJEC GCSE Chemistry (Wales) — 1.4 The ever-changing Earth · Explain · 4 marks

## Mark scheme (4 marks)

1. The red dye is a mixture (not a pure substance)
2. Three spots show that three different compounds are present / have separated
3. A pure substance would produce only a single spot
4. The result is the same in both solvents, which confirms the dye is a mixture (not a pure compound giving one spot in all solvents)

## Key terms

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

## Related

- [Revision notes for WJEC GCSE 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-colouring-manufacturer-claims-that-77f4bfa4) · Published by Druglandscape Ltd.