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Oxidisation & Reduction

Chemistry: Edexcel IGCSE, topic 10.1.9

Oxidation and Reduction

Oxidation is the gaining of oxygen in a reaction and reduction is the loss of oxygen in a reaction. We can describe oxidation and reduction in terms of electrons:

Oxidation

Oxidation

  • When a substance is oxidised (gains oxygen), it always loses electrons.
  • An oxidising agent gains an electron and oxidises another substance in a chemical reaction.
Reduction

Reduction

  • When a substance is reduced (loses oxygen), it always gains electrons.
  • A reducing agent loses an electron and reduces another substance in a chemical reaction.
OILRIG

OILRIG

  • A useful mnemonic for remembering the difference between oxidation and reduction reactions in terms of electrons is OIL RIG:
  • Oxidation
  • Is
  • Loss
  • Reduction
  • Is
  • Gain

Test yourself on Oxidisation & Reduction

  • Mg(s) + 2H+(aq) + 2Cl-(aq) → Mg2+(aq) + 2Cl-(aq) + H2(g)
    In this ionic equation, what's being oxidised and what's being reduced?

  • What type of reaction is happening to the zinc atoms?

  • 2Mg + O2 → 2MgO.

    Magnesium atoms lose electrons to form Mg2+ ions, and oxygen atoms gain electrons to form O2- ions.

  • What happens to a substance when it is reduced?

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