# Titanium dioxide nanoparticles are used in some sunscreen products. Explain why manufacturers choose to use titanium dioxide in the form of nanoparticles rather than as a bulk powder.

> AQA GCSE Chemistry (8462) — 4.2.4 Bulk and surface properties including nanoparticles (Chem only) · Explain · 4 marks

> Titanium dioxide is a white solid that absorbs ultraviolet (UV) radiation. In bulk form it leaves a visible white residue on skin. When used as nanoparticles, the sunscreen appears transparent on the skin.

## Mark scheme (4 marks)

1. Nanoparticles have a much larger surface area to volume ratio than the bulk material
2. The greater surface area to volume ratio means nanoparticles are more effective at absorbing UV radiation (per unit mass)
3. Nanoparticles can exhibit different properties to the same material in bulk
4. Nanoparticles are too small to scatter visible light so the sunscreen appears transparent/colourless on skin (unlike bulk powder which appears white)

## Key terms

- [nanoparticles](https://www.gradenine.co.uk/glossary/nanoparticles)
- [bulk](https://www.gradenine.co.uk/glossary/bulk)

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/titanium-dioxide-nanoparticles-are-used-in-13ecba31) · Published by Druglandscape Ltd.