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AQA · GCSE · Chemistry · Higher

Alloy structure and hardness

Q01.2 3 marks

Mixtures of copper and zinc are heated to produce alloys.

Figure 2 represents the structures of pure copper and of an alloy of copper and zinc.

Figure 2
Figure 2

Figure 2

Enlarged question image

Figure 2

Explain why the alloy of copper and zinc is harder than pure copper. Use Figure 2.

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Marking points

  1. 1 States that the alloy contains atoms of different sizes.
  2. 2 Links the different atom sizes to distorted layers.
  3. 3 Explains that the distorted layers cannot easily slide over each other.

Full-mark answer

Copper and zinc atoms are different sizes, so the regular layers are distorted. This stops the layers of atoms sliding over one another easily, making the alloy harder than pure copper.

Why this answer loses marks

The zinc atoms make the bonds stronger.

The credited explanation uses different-sized atoms distorting the layers so they cannot slide easily; stronger bonds are not the mechanism shown.

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