# A technician is testing a sample of a yellow paint pigment to check whether it is a pure substance or a mixture. She uses paper chromatography with two different solvents. In both solvents, the sample produces only a single spot on the paper. Explain what these results tell the technician about the yellow pigment, and describe one further test she could carry out to confirm that the pigment is a pure substance.

> WJEC GCSE Chemistry (Wales) — 1.1 The nature of substances and chemical reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. A pure compound produces a single spot in all solvents (so the single spot in both solvents suggests the pigment is a pure substance / not a mixture)
2. A mixture would separate into more than one spot, so the absence of multiple spots suggests the pigment is not a mixture
3. Further test: measure / determine the melting point of the pigment
4. A pure substance has a sharp / specific melting point, whereas a mixture melts over a range of temperatures

## Key terms

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

## Related

- [Revision notes for WJEC GCSE 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-technician-is-testing-a-sample-c429caa2) · Published by Druglandscape Ltd.