Properties and uses of some metals
3 marks · NormalBrass is an alloy of copper and zinc, and is often used for making musical instruments.
Explain, in terms of its structure, why brass is harder than pure copper. Your answer should refer to the arrangement of atoms.
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.
Show answer
Must show: zinc atoms are different size to copper atoms, disrupts regular lattice, prevents layers sliding easily
Also accept: Brass contains atoms of different sizes which distort layers; Brass is a mixture so lattice is irregular
Common mistakes: Brass has more atoms; Brass has stronger bonds (not explanation at syllabus level)
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Mentions that brass contains atoms of different sizes from the different metals.
M2 · 1 mark · Explains the different sized atoms disrupt the regular arrangement/lattice.
A1 · 1 mark · States that this makes it harder for the layers to slide, increasing hardness.
Worked solution
Brass is an alloy containing copper and zinc atoms, which are different sizes. This difference in size disrupts the regular arrangement and breaks up the layers of atoms, making it more difficult for the layers to slide over each other. As a result, brass is harder than pure copper.