Using metals

Metals show a wide range of different properties.

They have a range of melting points. For example, mercury is a liquid at room temperature, but tungsten has melting point of over 3400°C.

They have a range of reactivities. For example, potassium reacts violently with water, but gold does not react, even with concentrated acids.

It is important to choose the right metal for a particular purpose, depending on its properties. We would not choose to make a saucepan out of a metal with a low melting point, or a boat from a metal which reacts with water.

Aluminium, copper, iron and titanium

These metals show a range of properties, which relate to the uses of the metals.

MetalPropertyUses
AluminiumLow density. Resistant to corrosion.Aircraft. Electricity power cables.
CopperGood conductor of electricity. Very malleable and resistant to water corrosion. Electrical wiring. Water pipes.
IronPure iron is brittle, so is usually converted to steel. Steel is strong. Buildings. Cars. Tools.
TitaniumStrong Low density. Resistant to corrosion.Aircraft. Artificial hip joints.

As well as having the right physical properties for a particular use, it is also important to consider the cost of the metal. This will depend on its abundance, but also the method used to extract it.

For example, although copper is a very good conductor of electricity, it is not as good as silver. However, silver is much more rare and therefore more expensive.

The table shows that both aluminium and titanium can be used to make aircraft, as both metals have a low density and are resistant to corrosion. Titanium is much more expensive, as its extraction process is more complicated. Therefore, it is used for expensive military aircraft, where extra strength is an important factor, but commercial aircraft use aluminium.

Question

The table shows the properties of four metals.

MetalReactivityDensityConductivity
AluminiumForms an unreactive oxide layer2.71 g/cm33.5
IronRusts slowly in air7.85 g/cm31
SilverUnreactive11.3 g/cm36
SodiumReacts vigorously with water0.98 g/cm32

Which metal would you choose to make overhead power lines? Explain your choice.

To make electricity power cables, the metal should be a good conductor but it also needs to have low density, otherwise the power cables will sag and may break under their own weight. It is also important that the cables will not corrode in the atmosphere.

The best choice is aluminium - it is unreactive, with a low density and a high conductivity.