Knowledge Organiser: Oxidation and Reduction (Redox)
Key Terms
- Oxidation: loss of electrons (OIL)
- Reduction: gain of electrons (RIG)
- Redox: both occur simultaneously
- Reducing agent: donates electrons (is itself oxidised)
- Oxidising agent: accepts electrons (is itself reduced)
- OIL RIG / LEO GER: key mnemonics
Must-Know Facts
- Oxidation and reduction always happen together
- Oxidation = loss of e⁻ OR gain of O OR loss of H
- Reduction = gain of e⁻ OR loss of O OR gain of H
- Half equations: e⁻ on right (oxidation), left (reduction)
- Anode = oxidation; Cathode = reduction (OARC)
- Displacement, combustion, rusting = all redox
Key Equations
- Mg → Mg²⁺ + 2e⁻ (oxidation half-equation)
- Cu²⁺ + 2e⁻ → Cu (reduction half-equation)
- 2Fe₂O₃ + 3C → 4Fe + 3CO₂ (reduction of iron oxide by carbon)
Common Mistakes
- Confusing the reducing agent and oxidising agent: The reducing agent DONATES electrons (is itself oxidised); the oxidising agent ACCEPTS electrons (is itself reduced)
- Saying only electron transfer counts as redox: Redox also includes gaining/losing oxygen or hydrogen — combustion and rusting are redox reactions
- Writing half-equations with unbalanced charges: Both atoms and charges must balance — check the total charge on each side matches
- Forgetting OARC: At the Anode = Oxidation; at the Cathode = Reduction — applies to electrolysis and electrochemical cells
Memory Aid
- OIL RIG — the most important mnemonic in chemistry:
- Oxidation Is Loss Reduction Is Gain
- Write OIL RIG in the margin of your exam paper the moment you start. It earns marks every time.
- LEO GER — a second mnemonic:
- Lose Electrons = Oxidation Gain Electrons = Reduction
- "LEO the lion goes GER" — lose electrons oxidation, gain electrons reduction.
- Oxidising/reducing agents — the swap trick: "The oxidising agent is reduced. The reducing agent is oxidised." They do the opposite of what their name suggests happens to the other substance. Think: "The OXIDISING agent gets REDUCED (it gains electrons while making the other thing lose them)."
- Electrolysis reminder: OARC — Oxidation At anode, Reduction at Cathode. The vowels: A (anode) = oxidation, C (cathode) = reduction.