Redox Reactions

Oxidation and reduction

• Oxidation is the loss of electrons from a substance.

• It is also the gain of oxygen by a substance. For example, magnesium is oxidised when it reacts with oxygen to form magnesium oxide:

  • magnesium + oxygen → magnesium oxide
  • 2Mg + O2 → 2MgO

• Reduction is the gain of electrons by a substance. It is also the loss of oxygen from a substance.

  • For example, copper(II) oxide can be reduced to form copper when it reacts with hydrogen:
  • copper(II) oxide + hydrogen → copper + water
  • CuO + H2 → Cu + H2O

• Usually, oxidation and reduction take place at the same time in a reaction. We call this type of reaction a redox reaction (red – reduction, ox – oxidation).

Note that:

• the oxidising agent is the chemical that causes oxidation by providing oxygen

• the reducing agent causes the other chemical to be reduced by removing oxygen

• Take a look at the following thermite reaction:

  • aluminium + iron(III) oxide → iron + aluminium oxide
  • 2Al + Fe2O3 → 2Fe + Al2O3

• Aluminium has been oxidised. This means that the iron(III) oxide is the oxidising agent.

• We can also see that the iron(III) oxide has been reduced. This means that the aluminium is the reducing agent.