This guide covers IGCSE Chemistry redox reactions. You will revise oxidation (loss of electrons; gain of oxygen), reduction (gain of electrons; loss of oxygen), OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons), and oxidising and reducing agents.

Key concepts to revise

• Oxidation – Loss of electrons; gain of oxygen; increase in oxidation number (if used).
• Reduction – Gain of electrons; loss of oxygen; decrease in oxidation number.
• Redox – Both oxidation and reduction occur in the same reaction; one species loses electrons (oxidised), another gains (reduced).
• Oxidising agent – Accepts electrons; is reduced. Reducing agent – Donates electrons; is oxidised.

Exam tips and command words

• State – Whether a species is oxidised or reduced (loss or gain of electrons/oxygen).
• Identify – The oxidising agent (the one that is reduced) and the reducing agent (the one that is oxidised).
• Describe – What happens to the oxidation state or electrons in a half-equation.
• Write – Half-equations for oxidation (e.g. Mg → Mg2+ + 2e-) and reduction (e.g. Cu2+ + 2e- → Cu).

Common mistakes

• Confusing oxidising agent (gets reduced) with reducing agent (gets oxidised).
• Saying “oxygen is oxidised” (oxygen is often the oxidising agent; it is reduced to O2- or in compounds).
• Not balancing half-equations (same number of electrons lost and gained when combining).

Revision checklist

• Define oxidation and reduction in terms of electrons (OIL RIG) and in terms of oxygen.
• Identify which species is oxidised and which is reduced in a given reaction (e.g. displacement).
• State the oxidising agent and reducing agent in a reaction.
• Write simple half-equations (e.g. Fe → Fe2+ + 2e-; Cl2 + 2e- → 2Cl-).

Next steps

Book a free trial with an IGCSE Chemistry tutor to practise redox questions, or explore Tutopiya’s learning portal for more revision resources.