# Explain why nanoparticles of gold can appear red or purple in solution, whilst bulk gold appears yellow, and suggest one reason why this difference in properties is useful to scientists.

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

> Gold nanoparticles with diameters between 1 nm and 100 nm are used in medical diagnostic tests. Bulk gold, such as gold jewellery, has a familiar yellow colour. Gold nanoparticles in solution can appear red or purple.

## Mark scheme (4 marks)

1. Nanoparticles have a much larger surface area to volume ratio than bulk gold
2. The increased surface area to volume ratio means nanoparticles interact with light differently to bulk gold, causing the different colour
3. Nanoparticles can exhibit properties different to those of the same material in bulk (so gold nanoparticles have different properties to bulk gold)
4. The colour difference can be used to detect or identify substances / used as an indicator in diagnostic tests (any sensible suggestion that the colour change is a useful signal)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-nanoparticles-of-gold-can-2759ea99) · Published by Druglandscape Ltd.