alleryCryolite and fluorspar are added during electrolytic reduction of alumina chiefly to do what?
ARaise the melting point of the mixture
BLower the melting point of the mixture
CAct as the cathode in the cell
DSupply extra oxygen at the anode
Answer & Solution
Correct answer: B. Lower the melting point of the mixture
1. Pure alumina melts above 2000 degrees Celsius, which is hard and costly to maintain.
2. Cryolite (Na3AlF6) and fluorspar (CaF2) are added to the molten mixture.
3. They lower the melting point to about 1000 degrees Celsius.
4. This makes the electrolysis practical and cheaper to run.
5. Option about raising the melting point is wrong, as that would worsen the problem.
6. Option about acting as the cathode is wrong, as the graphite lining is the cathode here.
7. Option about supplying oxygen at the anode is wrong, as oxygen comes from the alumina, not these additives.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 8 "Metallurgy", p.113_
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