9.6.12 — Burning Anodes
Electrolytic Extraction of Aluminium · Cambridge IGCSE Chemistry 0620
Reference Diagram — Electrolysis Cell
Red bubbles = O₂ produced at anode · Blue pool = Al deposited at cathode
Section A — The Material
What material are the anodes made from in the industrial electrolytic extraction of aluminium?
State one property of carbon (graphite) that makes it suitable as an electrode material in the extraction of aluminium.
In the electrolysis of molten aluminium oxide, the cathode is made from steel. What material are the anodes made from, and why must they be the same material as the product of the anode reaction?
Give the name of the electrolyte used in the extraction of aluminium, and state the physical state it must be in for electrolysis to occur.
At which electrode — anode or cathode — is aluminium deposited during electrolysis? What charge do aluminium ions carry?
Section B — The Explanation
Explain why the carbon anodes need to be regularly replaced during the extraction of aluminium. [2]
The electrolysis is carried out at approximately 950 °C.
Write the word equation and the balanced symbol equation for the reaction that causes the carbon anodes to be consumed. [2]
A student says: 'The anodes burn away because the aluminium oxide is acidic and corrodes the carbon.' Identify the two errors in this statement. [2]
Explain, in terms of oxidation and reduction, what happens to the carbon anode. [2]
Suggest one economic and one environmental disadvantage of the carbon anodes burning away. [2]
Section C — Environmental Impact
Name the main greenhouse gas produced when the carbon anodes burn away during the extraction of aluminium.
Explain how carbon dioxide contributes to climate change. [2]
State one reason why the extraction of aluminium has a large carbon footprint, apart from the burning of the anodes.
Suggest two reasons why recycling aluminium is more environmentally friendly than extracting it from its ore. [2]
A factory produces 1000 kg of aluminium per day. Each tonne of aluminium produced burns away 0.5 kg of carbon anode. Calculate the mass of CO₂ released per day from burning anodes. (Relative atomic masses: C = 12, O = 16) [3]
C + O₂ → CO₂
🔑 Core Equation to Memorise
C + O₂ → CO₂
Carbon (anode) + Oxygen (produced at anode) → Carbon Dioxide (gas released)
Why replaced?
O₂ burns carbon at 950 °C → CO₂
Oxidation?
Carbon is oxidised (gains O₂)
Greenhouse?
CO₂ traps heat → global warming
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