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.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial