Electrolysis - GCSE Chemistry Cheat Sheet (DRAFT) by [deleted]

Depending on a metal's reacti­vity, different methods of extraction are used.

If the metal is less reactive than carbon, then a reduction reaction (involving carbon) is used. This works because the carbon forms compounds more readily, so it 'steals' the oxygen (similar to displa­cement reacti­ons). An example of this is iron, which is extracted using a blast furnace.

If the metal is more reactive than carbon, electr­olysis must be used, as the metal's compounds are very stable. An example of this is aluminium extrac­tion.

1. Bauxite is purified to produce pure aluminium oxide (Al2O3).
2. The aluminium oxide is dissolved in cryolite (another aluminium ore). This introduces impuri­ties, reducing the melting temper­ature of the mixture to 900^°C.
3. The aluminium oxide is melted.
4. When a current is passed through it, the positive Al³⁺ ions are attracted to the cathode (negative electr­ode), where they gain electrons. This is reduction.
5. The negative O^2- electrons are attracted to the anode (positive electr­ons), where they lose electrons and form oxygen or carbon dioxide. This is oxidation.

Half equations:
    Al³⁺ + 3e^-  Al
    2O^2-  O2 + 4e^-

Reducing iron ore to iron:
1. Hot air is added to the blast furnace, as this makes the coke burn faster and elevates the temper­ature to around 1500^°C.
2. The coke burns and produces carbon dioxide.
  C + O2  CO2
3. The carbon dioxide reacts with any unburnt coke.
  CO2 + C  2CO
4. The carbon monoxide reduces the iron ore to iron.
  3CO + Fe2O3  3CO2 + 2Fe

Purifying the resulting iron:
The main impurity is silicon dioxide (sand).

1. Limestone is thermally decomposed into calcium oxide.
  CaCO3  CaO + CO2
2. Calcium oxide reacts with silicon dioxide to form slag.
  CaO + SiO2  CaSiO3