# A paint manufacturer produces a new green paint. A quality control technician uses paper chromatography to check whether the green pigment in the paint is a pure substance or a mixture of pigments. After running the chromatography, the technician observes that the green pigment separates into two spots on the paper. Explain what this result tells the technician about the green pigment, and describe how paper chromatography works to produce this result.

> WJEC A-Level Chemistry (Wales) — 1.4 States of matter · Explain · 5 marks

> A paint manufacturer produces a new green paint. A quality control technician uses paper chromatography to check whether the green pigment in the paint is a pure substance or a mixture of pigments. After running the chromatography, the technician observes that the green pigment separates into two spots on the paper.

## Mark scheme (5 marks)

1. The green pigment is a mixture (not a pure substance), because a pure substance produces only a single spot in all solvents.
2. The paper acts as the stationary phase (the non-moving phase).
3. The solvent acts as the mobile phase and carries the pigments up the paper.
4. The two pigments separate because they have different solubilities in the mobile phase / they are distributed differently between the mobile and stationary phases.
5. The Rf value of each spot can be used to identify the individual pigments / substances in the mixture.

## Key terms

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

## Related

- [Revision notes for WJEC A-Level 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-paint-manufacturer-produces-a-new-ff420430) · Published by Druglandscape Ltd.