# A student carries out paper chromatography on a food dye. The chromatogram produces three separate spots. Explain what this result tells the student about the food dye, and describe how the student could use Rf values to help identify the substances present.

> AQA GCSE Chemistry (8462) — 4.8.1 Purity, formulations and chromatography · Explain · 4 marks

## Mark scheme (4 marks)

1. The food dye is a mixture (not a pure substance) / contains three components / is not a single compound
2. A pure compound would produce only one spot (in any solvent)
3. The Rf value is calculated as the distance moved by the substance divided by the distance moved by the solvent
4. The Rf values of the spots can be compared to known/reference Rf values (in the same solvent) to identify each substance

## Key terms

- [chromatography](https://www.gradenine.co.uk/glossary/chromatography)
- [Rf value](https://www.gradenine.co.uk/glossary/rf-value)

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](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-carries-out-paper-chromatography-684a78f4) · Published by Druglandscape Ltd.