# Explain why stainless steel is harder and stronger than pure iron.

> Cambridge International IGCSE Chemistry (0620) — 9.3 Alloys and their properties · Explain · 4 marks

> Stainless steel is an alloy made by mixing iron with chromium and nickel. Pure iron is a relatively soft metal that is rarely used on its own in construction.

## Mark scheme (4 marks)

1. In pure iron the atoms are all the same size and arranged in regular layers
2. The layers can slide over each other easily (in pure iron)
3. In stainless steel, atoms of different sizes are present (chromium / nickel atoms are different sizes to iron atoms)
4. The different-sized atoms distort / disrupt the layers, preventing them from sliding, making the alloy harder

## Key terms

- [pure iron](https://www.gradenine.co.uk/glossary/pure-iron)
- [stainless steel](https://www.gradenine.co.uk/glossary/stainless-steel)

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](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-stainless-steel-is-harder-5ef9e47c) · Published by Druglandscape Ltd.