2.5 Extraction & Uses of MetalsEdexcel IGCSE Chemistry: Revision notes
Section 1
Where do metals come from?
Most metals are found combined with other elements in ores, rock or mineral deposits from which a metal can be extracted profitably. Very unreactive metals, such as gold, are found in the Earth's crust as the uncombined element, because they do not readily react with other substances like oxygen.
Section 2
How does extraction method depend on reactivity?
The method used to extract a metal from its ore depends on the metal's position in the reactivity series:
| Reactivity | Extraction method | Example |
|---|---|---|
| Very unreactive | Found native (uncombined) | Gold |
| Moderately reactive (below carbon) | Reduction using carbon | Iron |
| Very reactive (above carbon) | Electrolysis of the molten compound | Aluminium |
Iron is extracted by reduction with carbon in a blast furnace: iron oxide is reduced as carbon (or carbon monoxide) removes the oxygen, since carbon is more reactive than iron.
Aluminium is more reactive than carbon, so carbon cannot reduce it. Instead, aluminium is extracted by electrolysis of molten aluminium oxide (dissolved in molten cryolite to lower its melting point and reduce energy costs).
When commenting on an unfamiliar metal extraction, always link the method chosen to the metal's position relative to carbon in the reactivity series.
Section 3
How are aluminium, copper, iron and steel used?
Uses relate directly to physical properties:
- Aluminium: low density, resistant to corrosion (forms a protective oxide layer) — used in aircraft, drink cans, overhead power cables.
- Copper: excellent electrical conductor, malleable, resistant to corrosion — used in electrical wiring and water pipes.
- Iron and steel: steel is an alloy of iron; different types suit different uses:
- Low-carbon steel: softer and more easily shaped — used for car bodies.
- High-carbon steel: harder but more brittle — used for cutting tools/blades.
- Stainless steel: contains chromium/nickel, resistant to corrosion — used for cutlery and kitchen equipment.
Section 4
What are alloys and why are they harder than pure metals?
An alloy is a mixture of a metal with one or more other elements (often other metals or carbon). Steel (iron + carbon), brass (copper + zinc) and bronze (copper + tin) are common alloys.
In a pure metal, atoms are the same size and arranged in regular layers that can slide over each other easily, making pure metals soft and malleable.
In an alloy, the different-sized atoms added distort the regular layers, making it harder for the layers of atoms to slide over one another. This is why alloys are generally harder than the pure metals they are made from.
Think of a pure metal as neatly stacked same-size marbles that slide past each other easily; an alloy is like mixing in different-sized marbles, which jam the layers and stop them sliding as freely.
Must Know
- Metals are extracted from ores; very unreactive metals (e.g. gold) occur uncombined.
- Extraction method depends on reactivity relative to carbon: reduction with carbon (e.g. iron) for metals below carbon; electrolysis (e.g. aluminium) for metals above carbon.
- Iron is extracted by reduction with carbon in a blast furnace; aluminium by electrolysis of molten aluminium oxide.
- Aluminium: low density, corrosion resistant. Copper: good electrical conductor. Steel types: low-carbon (soft, car bodies), high-carbon (hard, tools), stainless (corrosion-resistant, cutlery).
- An alloy is a mixture of a metal with other elements.
- Alloys are harder than pure metals because different-sized atoms distort the regular layers, preventing them sliding easily.
That's the notes covered.
Carry on to the next subtopic.