Properties and uses of some metals
5 marks · HardA coin is made from an alloy containing copper and nickel.
Define the term 'alloy'.
Explain, in terms of atomic structure, why this alloy is harder than either pure copper or pure nickel.
Suggest one advantage of using the alloy instead of pure copper for making coins.
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 elements, usually other metals or carbon.
(b) The different sized atoms in the alloy disrupt the regular arrangement of atoms, making it harder for the layers to slide over each other, so the alloy is harder. · must show Different sized atoms, Disruption of regular lattice, Layers cannot slide easily
(c) The alloy is more durable/harder and coins made from it are less likely to wear down or lose their shape over time.
Common mistakes: Not mentioning different sized atoms in the structure explanation.; Reversing alloy and pure metal properties.; Only giving 'it is harder' as an advantage, but not relating to coin durability or wear.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct definition of an alloy.
M1 (b) · 1 mark · Mentions different sized atoms/elements in the alloy.
M2 (b) · 1 mark · States that the regular lattice/structure is disrupted (or continuity of layers is broken).
A1 (b) · 1 mark · Concludes that layers cannot slide over each other, making the alloy harder.
B2 (c) · 1 mark · States a valid advantage of using the alloy (e.g., more durable, resists wear, does not deform easily).
Worked solution
(a) An alloy is a mixture of a metal with other elements, usually other metals or carbon.
(b) In an alloy, such as copper and nickel, the atoms are different sizes. This disrupts the regular arrangement of atoms found in a pure metal and breaks up the lattice. As a result, the layers cannot slide over each other easily, so the alloy is harder than either pure metal.
(c) Coins made from the alloy are harder and more durable than those made from pure copper, so they do not wear down as quickly.