alleryStart learning →In the Hall–Héroult process, cryolite ($Na_3AlF_6$) is added to alumina to
Aremove iron and silicon oxide impurities
Bdecrease the electrical conductivity of the melt
Cserve as the sacrificial carbon anode
Dlower the fusion temperature and raise conductivity
Answer & Solution
Correct answer: D. lower the fusion temperature and raise conductivity
1. Pure alumina melts near 2300 K, which is impractical to electrolyse.
2. Dissolving alumina in molten cryolite lowers the working temperature (~1270 K) and increases the electrical conductivity of the melt.
3. Calcium chloride is also added to lower the melting point further.
_Source: Samacheer Kalvi Class 12 Chemistry Vol.1, Unit 1 'Metallurgy', §1.5.1 / Evaluation Q.13_
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