# A food technologist is investigating two fruit squash drinks, Sample A and Sample B. Both drinks appear identical in colour. The technologist carries out paper chromatography on each sample using the same solvent. Sample A produces three separate spots on the chromatogram. Sample B produces only one spot. The spot produced by Sample B has the same Rf value as one of the spots produced by Sample A. Explain what the results of this chromatography investigation tell the technologist about the composition of each sample, and explain why the Rf values are useful in identifying the substances present.

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

> A food technologist is investigating two fruit squash drinks, Sample A and Sample B. Both drinks appear identical in colour. The technologist carries out paper chromatography on each sample using the same solvent. Sample A produces three separate spots. Sample B produces only one spot. The spot produced by Sample B has the same Rf value as one of the spots produced by Sample A.

## Mark scheme (5 marks)

1. Sample A is a mixture because it produces more than one spot / contains more than one substance
2. Sample B is a pure substance because it produces only a single spot (in this solvent)
3. The Rf value is calculated as the distance travelled by the dissolved substance divided by the distance travelled by the solvent
4. Different compounds have different Rf values (in the same solvent), so Rf values can be used to identify the substances present
5. Because Sample B has the same Rf value as one spot in Sample A, the same compound/substance is present in both samples

## Key terms

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

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-food-technologist-is-investigating-two-64328827) · Published by Druglandscape Ltd.