Chem6 Flashcards
Why are graphite anodes replaced in aluminum extraction?
O₂ reacts with them: 2C(s) + ³⁄₂O₂(g) → CO(g) + CO₂(g), causing decay.
What two advantages do modern fluoride salt mixtures have over cryolite?
- Lower melting point (saves energy).
- Lower density (eases Al separation).
At which electrode does metal deposition always occur?
Cathode (reduction site).
What gases form when graphite reacts with oxygen?
CO and CO₂.
Why is lowering the melting point crucial in aluminum extraction?
Reduces energy costs (from 2045°C → 950°C).
How does lower density of the modern mixture help?
Molten aluminum sinks more easily for collection.
What is the key difference between cryolite and the modern fluoride mixture?
The modern mix has Na/Ca/Al fluorides (not just NaAlF₆).
What happens to aluminum ions (Al³⁺) during electrolysis?
They gain electrons at the cathode: Al³⁺ + 3e⁻ → Al(l).
What type of reaction occurs at the anode in all three experiments?
Oxidation (loss of electrons).
What is the primary energy cost in aluminum extraction?
Electricity for electrolysis (hence the need for lower MP mixtures).
Why is fluorspar (CaF₂) added to the aluminum extraction mix?
Lowers melting point further, saving energy.
What is the industrial name for the aluminum extraction process?
Hall-Héroult process.
