# Metals used in engineering are often alloys rather than pure metals. Explain why alloys are harder than pure metals, and describe one use of alloys that makes use of this property.

> OCR GCSE Chemistry A: Gateway Science (J248) — C2.3 Properties of materials · Explain · 4 marks

> Steel is an alloy of iron and carbon. It is used extensively in construction and manufacturing because it is significantly harder than pure iron.

## Mark scheme (4 marks)

1. In a pure metal, the atoms are all the same size and arranged in regular layers that can slide over each other easily.
2. In an alloy, atoms of different sizes are present, which distort the regular arrangement / layers.
3. This makes it more difficult for the layers to slide over each other, so the alloy is harder / stronger than the pure metal.
4. A suitable use of an alloy that relies on greater hardness or strength, e.g. steel used in construction/bridges/buildings, bronze used for tools or medals, duralumin used in aircraft frames.

## Key terms

- [alloy](https://www.gradenine.co.uk/glossary/alloy)
- [pure metal](https://www.gradenine.co.uk/glossary/pure-metal)

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](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/metals-used-in-engineering-are-often-9d57bbf5) · Published by Druglandscape Ltd.