Properties and uses of some metals
3 marks · EasyBrass is an alloy made from copper and zinc. Use your knowledge of alloys to answer the following:
Define the term "alloy."
Explain, in terms of structure, why brass is harder than pure copper.
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) An alloy is a mixture of a metal with other metals or carbon.
(b) Brass is harder because the different sized atoms from copper and zinc disrupt the regular layers so they cannot slide over each other as easily.
Common mistakes: Brass is harder because it is heavier or denser.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Defines alloy as a mixture of a metal with other metals or carbon.
M1 (b) · 1 mark · States that the different atoms in the alloy break up the regular lattice or arrangement (or use similar phrasing).
A1 (b) · 1 mark · Links this structure to increased hardness by stating that layers cannot slide over each other as easily as in pure copper.
Worked solution
a) An alloy is a mixture of a metal with other metals or carbon.
b) In brass, the atoms of zinc are a different size than the copper atoms. This disrupts the regular arrangement of copper atoms. As a result, it is harder for the layers to slide over one another, making brass harder than pure copper.