ElectrolysisTopic Summary

Knowledge Organiser: Electrolysis of Aluminium

Part of Electrolysis of Aluminium · GCSE GCSE Chemistry revision

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 20 exam-style questions and 0 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. 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.

Topic position

Section 13 of 13

Practice

20 questions

Recall

0 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

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Worked Model Answer The Metal That Changed History Electrolysis of Aluminium Oxide

Practice Questions for Electrolysis of Aluminium

Why is aluminium extracted by electrolysis rather than by reduction with carbon?

A. Aluminium is less reactive than carbon
B. Aluminium is more reactive than carbon
C. Aluminium does not form ions
D. Carbon reacts with aluminium to form carbides

1 markfoundation

Explain why aluminium is extracted by electrolysis rather than by reduction with carbon.

2 marksstandard

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.

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Worked Model Answer

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Electrolysis of Aluminium