# A student uses paper chromatography to investigate two dyes, dye X and dye Y. Dye X produces a single spot. Dye Y produces three spots. Explain what these results tell the student about the composition of each dye, and describe how the Rf value of the single spot from dye X could be used to help identify it.

> AQA GCSE Chemistry (8462) — 4.8.3 Identification of ions by chemical and spectroscopic means (Chem only) · Explain · 4 marks

## Mark scheme (4 marks)

1. Dye X is a pure substance / single compound (because it produces only one spot)
2. Dye Y is a mixture (because it produces more than one spot / separates into three spots)
3. The Rf value is calculated as the distance moved by the substance divided by the distance moved by the solvent
4. The Rf value of dye X's spot can be compared to known / reference Rf values (in the same solvent) to identify the compound

## 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-uses-paper-chromatography-to-9cfb2243) · Published by Druglandscape Ltd.