# A student tests an unknown sports drink using paper chromatography. The chromatogram shows three spots for the sports drink. The student also runs a sample of pure riboflavin (a food colourant) alongside it, which produces a single spot with an Rf value of 0.45. One of the spots from the sports drink has an Rf value of 0.45 in the same solvent. Explain what the student can conclude about the sports drink from these results.

> 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. The sports drink is a mixture (not a pure substance) because it produces more than one spot
2. The sports drink contains riboflavin because one spot has the same Rf value (0.45) as pure riboflavin
3. The other two spots represent different compounds / components that are not riboflavin
4. Rf values depend on the solvent used, so the same solvent must be used for a valid comparison / the identification is only valid in this solvent

## Key terms

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

## 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-tests-an-unknown-sports-849653fd) · Published by Druglandscape Ltd.