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Cambridge O Level Chemistry 5070 — 9.3 Alloys and their Properties — Cambridge O Level Chemistry 5070 Revision Notes & Topical Questions

5 min read 5 parts Lesson 3 of 6

📚 Cambridge O Level Chemistry 5070 Hub / Topical Revision
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Lesson summary

9.3 Alloys and their Properties — Cambridge O Level Chemistry: define an alloy, explain why alloys are usually harder than pure metals, and link named alloys to their uses. An alloy is a mixture containing a metal and one or more other elements.

  • Exam explanation
  • Brass and stainless steel
  • Other useful combinations

Part 1 of 5What is an alloy?

What is an alloy?
An alloy is a mixture containing a metal and one or more other elements. The added elements may be metals, as in brass, or non-metals, as in steel containing carbon. An alloy is a mixture rather than a compound: its components are not chemically combined in one fixed ratio.
Changing an alloy's composition can change its hardness, strength, corrosion resistance or ability to tolerate high temperatures. These properties can make an alloy more useful for a particular purpose than the pure metal.

Part 2 of 5Why alloys are harder

In a pure metal, similarly sized atoms form regular layers that can slide past each other when a force is applied. An alloy contains atoms of different sizes. These disturb the regular layers and make sliding more difficult, so the alloy is often harder and less easily bent.
Exam explanation
For a hardness question, connect all three ideas: different-sized atoms, distorted layers, and reduced ability of the layers to slide. Saying only that the alloy is a mixture does not explain its hardness.

Part 3 of 5Named alloys and uses

1Brass and stainless steel
Brass contains copper and zinc.
  • It is stronger and harder than pure copper and can be used for door handles, ornaments and musical instruments.
  • Stainless steel contains iron with other elements such as chromium, nickel and carbon.
  • Its hardness and resistance to corrosion make it suitable for cutlery.
2Other useful combinations
Iron alloys containing tungsten can remain hard at high temperatures.
  • Chromium or nickel can improve the corrosion resistance of iron alloys.
  • Aluminium alloys containing elements such as copper, manganese or silicon can provide greater strength while keeping a low density,
  • which is useful for aircraft structures.

Part 4 of 5Worked comparison

Worked comparison
Why might an aircraft use an aluminium alloy instead of pure aluminium? The alloy keeps aluminium's low density while giving greater strength. Different-sized added atoms disrupt sliding of the metal layers, making the material harder and stronger.
Do not call an alloy a compound. The metal and added elements form a mixture, and the proportions can be adjusted to obtain suitable properties.

Part 5 of 5Check your understanding

    • 1.
    • Define an alloy and give one example containing a non-metal.
    • 2.
    • Explain why alloys are often harder than pure metals.
    • 3.
    • Name the main metals in brass.
    • 4.
    • Link one property of stainless steel to a use.
    • 5.
    • Explain why a light, strong aluminium alloy is useful in aircraft.

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