Redox Reactions

OCR

GCSE

Redox reactions involve the simultaneous processes of oxidation and reduction, defined fundamentally by electron transfer and historically by oxygen transfer. Candidates must apply the mnemonic OIL RIG (Oxidation Is Loss, Reduction Is Gain) to identify species undergoing change in displacement, electrolysis, and extraction contexts. Mastery requires the construction of balanced half-equations to explicitly show electron movement and the identification of oxidizing and reducing agents within full ionic equations.

Objectives

Exam Tips

Pitfalls

Key Terms

Mark Points

What You Need to Demonstrate

Key skills and knowledge for this topic

Award 1 mark for defining oxidation as loss of electrons or gain of oxygen, and reduction as gain of electrons or loss of oxygen
Credit identification of the oxidising agent as the reactant that gains electrons (accept 'takes electrons from the other species')
Award 1 mark for explaining that a reaction is 'redox' because both oxidation and reduction occur simultaneously
For half-equations, award 1 mark for correct formulae of ions/atoms and 1 mark for balancing electrons on the correct side (LHS for reduction, RHS for oxidation)

Example Examiner Feedback

Real feedback patterns examiners use when marking

"You correctly identified the oxidation process, but check your definition of the 'agent' — remember the agent causes the process to happen to the other species"
"Your half-equation balances atoms, but look at the total charge on the left versus the right"
"Good use of 'OIL RIG'. Now apply this to explain why the metal ion is reduced at the cathode"
"To secure the mark, specify 'loss of electrons' rather than just 'electron transfer'"

Marking Points

Key points examiners look for in your answers

Award 1 mark for defining oxidation as loss of electrons or gain of oxygen, and reduction as gain of electrons or loss of oxygen
Credit identification of the oxidising agent as the reactant that gains electrons (accept 'takes electrons from the other species')
Award 1 mark for explaining that a reaction is 'redox' because both oxidation and reduction occur simultaneously
For half-equations, award 1 mark for correct formulae of ions/atoms and 1 mark for balancing electrons on the correct side (LHS for reduction, RHS for oxidation)

Examiner Tips

Expert advice for maximising your marks

💡Use the mnemonic OIL RIG (Oxidation Is Loss, Reduction Is Gain) specifically for electrons; do not mix this with oxygen definitions
💡When asked to identify an agent, always select a species from the left-hand side (reactants) of the equation
💡In 6-mark questions involving electrolysis, explicitly link the movement of ions to the electrode to the gain/loss of electrons

Common Mistakes

Pitfalls to avoid in your exam answers

Identifying a product as the oxidising or reducing agent rather than a reactant
Stating that the oxidising agent is the species being oxidised (confusion between agent and process)
Writing electrons on the wrong side of a half-equation (e.g., adding electrons to the right side for a reduction reaction)
Failing to balance the charge in half-equations, even if the atoms are balanced

Study Guide Available

Comprehensive revision notes & examples

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Key Terminology

Essential terms to know

Definitions of oxidation and reduction (electron and oxygen transfer)

Construction and balancing of half-equations

Identification of oxidizing and reducing agents

Ionic equations and spectator ions

Displacement reactions (Metals and Halogens)

Likely Command Words

How questions on this topic are typically asked

State

Explain

Identify

Construct

Write

Evaluate

Practical Links

Related required practicals

•{"code":"PAG C1","title":"Electrolysis of aqueous solutions","relevance":"Observing redox reactions at electrodes"}
•{"code":"PAG C3","title":"Displacement reactions","relevance":"Demonstrating electron transfer between metals/halogens"}

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