# A drinks manufacturer produces a new sports drink containing artificial colourings. A trading standards officer wants to check whether the colourings used match the approved list. The officer uses paper chromatography to analyse the drink. One colouring produces a single spot, while another produces three spots. Explain what the results tell the officer about each colouring, and describe how the officer could use Rf values to help identify whether the colourings are on the approved list.

> Eduqas A-Level Chemistry — 1.2 Electronic structure · Explain · 5 marks

> Paper chromatography separates substances depending on how soluble they are in the mobile phase. The Rf value is calculated as the distance travelled by the dissolved substance divided by the distance travelled by the solvent.

## Mark scheme (5 marks)

1. The colouring that produces a single spot is a pure substance / contains only one compound
2. The colouring that produces three spots is a mixture / contains three different compounds
3. The three compounds separate because they have different solubilities in the mobile phase / solvent, so they travel different distances up the paper
4. The officer calculates the Rf value for each spot by dividing the distance travelled by the substance by the distance travelled by the solvent
5. The calculated Rf values are compared to known Rf values of approved colourings (in the same solvent) to identify whether they match

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-drinks-manufacturer-produces-a-new-3ba166b5) · Published by Druglandscape Ltd.