# A student carries out an emulsion test on two food samples. Sample A gives a cloudy white emulsion. Sample B remains clear. Explain what the emulsion test involves, what the results show about the contents of each sample, and state the elements found in a lipid molecule.

> AQA A-Level Biology (7402) — 3.1.3 Lipids · Explain · 5 marks

> The emulsion test is used to detect the presence of lipids in a food sample.

## Mark scheme (5 marks)

1. The sample is mixed/shaken with ethanol (then water/aqueous solution added)
2. A cloudy white emulsion/milky-white layer forms if lipid is present
3. Sample A contains lipid (because it gives a positive / cloudy white result)
4. Sample B does not contain lipid (because it remains clear / gives a negative result)
5. Lipids contain carbon, hydrogen and oxygen (all three elements required for the mark)

## Key terms

- [emulsion test](https://www.gradenine.co.uk/glossary/emulsion-test)
- [lipid](https://www.gradenine.co.uk/glossary/lipid)
- [cloudy white emulsion](https://www.gradenine.co.uk/glossary/cloudy-white-emulsion)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-carries-out-an-emulsion-cd9a64ea) · Published by Druglandscape Ltd.