Properties and uses of some metals
4 marks · NormalThe diagrams below show simplified structures of a pure metal and an alloy. Study them and answer the questions.
Define the term 'alloy.'
Explain why alloys are usually harder than pure metals. You may use diagrams in your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) A mixture of a metal with other metals or carbon.
(b) Alloys are harder because the different sized atoms in the alloy disrupt the regular arrangement of metal atoms, making it more difficult for the layers to slide over each other. · must show different sized atoms, disrupted lattice, layers cannot slide easily, diagram with irregular arrangement (allowed)
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Marking points
B1 (a) · 1 mark · Correct definition of an alloy as a mixture of a metal with other elements (usually metals or carbon).
M1 (b) · 1 mark · States or diagrams that alloys have atoms of different sizes, disrupting the regular structure.
M2 (b) · 1 mark · Explains that this disruption makes it more difficult for layers to slide over each other.
A1 (b) · 1 mark · Links the structure to the increased hardness of alloys.
Worked solution
a) An alloy is a mixture of a metal with other metals or carbon.
b) In pure metals, the atoms are all the same size and arranged in a regular pattern. This allows the layers to slide over each other easily, so metals are soft.
In alloys, different metals have atoms of different sizes. This disrupts the regular arrangement and makes it harder for the layers to slide, so alloys are harder.