Edexcel IGCSE Chemistry · Spec 2.25C-2.27C
Uses of Metals & Alloys
The uses of common metals and why alloys are often more useful than pure metals.
Chemistry revision video
Uses of Metals & Alloys
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Explained
Choosing a metal, and improving it
Metals are chosen for jobs that suit their properties, and a question asking why a particular metal is used is asking you to name the property and link it to the job.
Common metals and why they are used
- Copper: an excellent conductor of electricity, ductile so it can be drawn into wires, and unreactive so it does not corrode. Used for wiring and for pipes.
- Aluminium: low density and resists corrosion, because a thin oxide layer forms on the surface and protects the metal underneath. Used for aircraft bodies, drinks cans and overhead power cables.
- Iron and steel: strong and cheap, so used for structures, vehicles and tools. Iron rusts, so it needs protecting.
- Gold: extremely unreactive, so it keeps its appearance, and a good conductor. Used for jewellery and for electrical contacts.
Aluminium is worth a second look, because it appears low in the reactivity series from its behaviour and high in it from its chemistry. It is genuinely reactive; it simply reacts once, immediately, with the air, and the oxide layer then seals the surface.
What an alloy is
An alloy is a mixture of a metal with one or more other elements, made deliberately to improve its properties. Steel is iron with carbon; brass is copper with zinc; bronze is copper with tin.
It is a mixture, not a compound. The elements are not chemically bonded in fixed proportions, which is why the composition can be varied to tune the properties.
Why alloys are harder
In a pure metal the atoms are all the same size and arranged in regular layers, which can slide over one another when a force is applied. That sliding is what makes a pure metal soft and malleable.
An alloy contains atoms of a different size, which disrupt the regular arrangement. The layers can no longer slide easily past each other, so the alloy is harder and less malleable than the pure metal.
That is the whole explanation, and both halves are marked: the different sized atoms, and the layers not being able to slide.
What the mark scheme accepts and rejects
An Edexcel International GCSE Chemistry mark scheme gives two marks for this explanation: one for layers or rows of atoms, ions or particles, and one for those layers being able to slide over one another.
Its notes then rule out two specific ways of getting it wrong. It rejects the first mark if molecules or intermolecular forces are mentioned, and it rejects the second if the answer says the electrons slide.
Both rejections protect the same idea. A metal is a lattice of positive ions in a sea of delocalised electrons, with no molecules anywhere in it, so intermolecular forces cannot apply. And it is the layers of ions that slide; the delocalised electrons are already free to move everywhere and their movement is what makes the metal conduct, not what makes it malleable.
Using the right particle for the right property is what these mark schemes are testing. Ions slide, electrons conduct.
Answering a uses question
Name the property, then say what it allows.
Copper is used for wiring because it conducts electricity well, so little energy is wasted, and because it is ductile, so it can be drawn into thin wires. Aluminium is used for aircraft because it has a low density, so the aircraft is lighter and needs less fuel.
Two clauses per property. A list of properties with no consequences attached is the answer that scores half.
Spec 2.25C-2.27C
What you need to know
- Link a metal's uses to its properties
- Say what an alloy is
- Explain why alloys are harder than pure metals
Active recall
Quick check
Answer each question before opening the answer.
What is an alloy and why is it harder than the pure metal?
A mixture of a metal with other elements; the different-sized atoms distort the layers so they cannot slide easily.
Give an example of an alloy and what it contains.
Steel (iron + carbon) or brass (copper + zinc).
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