# A scientist is testing a new sunscreen product. The scientist wants to find out whether the sunscreen is a pure substance or a formulation, and then uses crystallisation to obtain a solid component from it. Describe how the scientist could determine whether the sunscreen is a pure substance or a mixture, and outline the steps involved in crystallisation to obtain a solid from the sunscreen solution.

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

> A scientist is investigating the composition of a sunscreen product. The sunscreen is dissolved in water to produce a solution. The scientist suspects the sunscreen is a formulation rather than a pure substance.

## Mark scheme (5 marks)

1. A pure substance has a sharp/specific melting point whereas a mixture melts over a range of temperatures
2. Measure/determine the melting point of the sunscreen and compare it to known/data book values
3. A formulation is a mixture designed for a particular use, made up of exact quantities of pure substances — the sunscreen is likely a formulation because it contains multiple components for a specific purpose
4. Heat the sunscreen solution in an open container to evaporate the solvent until crystals begin to form / a saturated solution is produced
5. Allow the solution to cool so that crystals grow, then filter the crystals from the solution and allow them to dry

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-scientist-is-testing-a-new-912ce0ee) · Published by Druglandscape Ltd.