This topic summary covers Knowledge Organiser: Electrolysis of Aluminium within Electrolysis of Aluminium for GCSE Chemistry. Revise Electrolysis of Aluminium in Electrolysis for GCSE Chemistry with 21 exam-style questions and 14 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 13 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Electrolysis of Aluminium
Key Terms
- Electrolysis — decomposition using electricity
- Cathode — negative electrode (reduction)
- Anode — positive electrode (oxidation)
- Cryolite — solvent that lowers melting point
- Bauxite — aluminium ore (contains Al₂O₃)
- Half equation — equation showing electron transfer
Must-Know Facts
- Al is too reactive for carbon reduction
- Cryolite lowers mp from 2072°C to ~950°C
- Cathode: Al³⁺ + 3e⁻ → Al (reduction)
- Anode: 2O²⁻ → O₂ + 4e⁻ (oxidation)
- Anodes burn away: C + O₂ → CO₂
- Recycling saves 95% of energy
- Overall: 2Al₂O₃ → 4Al + 3O₂
Key Equations
- Al³⁺ + 3e⁻ → Al (cathode — reduction)
- 2O²⁻ → O₂ + 4e⁻ (anode — oxidation)
- 2Al₂O₃ → 4Al + 3O₂ (overall equation)
- C + O₂ → CO₂ (anode burning away)
Common Mistakes
- Saying aluminium forms at the anode: Aluminium is a positive ion (cation) so it moves to the CATHODE (negative) — metals always form at the cathode
- Forgetting why anodes need replacing: The carbon anodes react with oxygen produced at the anode to form CO₂ — they burn away and must be regularly replaced
- Saying cryolite is used to purify aluminium: Cryolite is a solvent that dissolves aluminium oxide and lowers its melting point — it does not purify the product
- Not balancing the half-equations for charge: Al³⁺ + 3e⁻ → Al — the 3 electrons balance the 3+ charge on aluminium
Practice questions for Electrolysis of Aluminium
Why is aluminium extracted by electrolysis rather than by reduction with carbon?
Explain why aluminium is extracted by electrolysis rather than by reduction with carbon.
Quick recall flashcards
What does OIL RIG stand for?
Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
At the Anode = Oxidation (loss). At the Cathode = Reduction (gain).
Why do the carbon anodes need replacing regularly?
At 950°C, the oxygen produced at the anode reacts with the hot carbon: C + O₂ → CO₂. The carbon is gradually burned away, so the anodes must be replaced periodically.