Alloys as useful materials — AQA GCSE Chemistry
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Alloys as useful materials explained
Steel is an alloy based on iron. It always contains iron as the main metal, together with a controlled, specific amount of carbon and often other metals added for particular properties.
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The carbon content is chosen deliberately: low carbon steel and high carbon steel have different properties because their carbon percentages differ. Other metals may be added to make alloy steels with extra strength, hardness or resistance to corrosion; stainless steel, for example, contains chromium. Because the amounts are specific, steel is not a single substance but a family of alloys whose composition is adjusted for a purpose.
Your focus
- Describe steel as an alloy of iron containing controlled amounts of carbon and other metals.
- Explain how the composition of a steel is linked to its properties.
- Give an example of an alloy steel and a property gained from its added metal.
Alloys as useful materials exam tips
Marking Points
- State that steel is a mixture of iron with carbon and possibly other metals.
- Explain that the carbon content is a controlled, specific amount rather than a random or unlimited quantity.
- Recognise that changing the amount of carbon or the identity of other added metals changes the properties of the steel.
- Give a named example of an alloy steel, such as stainless steel containing chromium, and link the added metal to a property.
- Distinguish steel from pure iron by noting that pure iron is an element while steel is an alloy.
Examiner Tips
- 💡Name the main metal first, then the added elements, when describing the composition of a steel.
- 💡Use comparative language such as higher carbon content or added chromium when explaining property differences.
- 💡Link each composition feature to a use, for example corrosion resistance for stainless steel.
Common Mistakes
- Describing steel as pure iron; correct this by stating that steel is an alloy of iron with carbon and often other metals.
- Thinking any amount of carbon can be present; correct this by explaining that the carbon content is deliberately controlled to give specific properties.
- Assuming all steels have identical properties; correct this by linking differences in composition, such as carbon content or added chromium, to differences in properties.