Metals, Extraction and Properties of Materials
Core ideas
The reactivity series ranks metals by their tendency to lose electrons. Metals above carbon are extracted by electrolysis; metals below carbon can be reduced by carbon. Iron is extracted in a blast furnace using coke, limestone and air. Aluminium is extracted by electrolysis of molten aluminium oxide dissolved in cryolite. Alloys are mixtures of metals that improve properties (e.g. steel, brass). Corrosion of iron requires oxygen and water; rusting can be prevented by painting, greasing, galvanising or sacrificial protection.
Properties of materials depend on structure: metals are malleable and conduct; ceramics are hard and brittle; polymers are long-chain molecules. Recycling conserves resources and energy.
Traps to watch
- Gold and silver occur native; reactive metals do not.
- Galvanising protects iron by a barrier and by sacrificial action.
- Aluminium is not extracted by carbon reduction because it is too reactive.
- Alloys have different properties from pure metals; they are usually harder.
Rule of thumb
Above carbon → electrolysis; below carbon → carbon reduction. For rust prevention, exclude oxygen or water, or use a more reactive metal.
Worked example
Explain why aluminium is extracted by electrolysis rather than carbon reduction. Aluminium is more reactive than carbon, so carbon cannot displace it from its oxide; electrolysis of molten aluminium oxide is required.