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Question

Which among the following statement(s) is(are) true for the extraction of aluminium from bauxite?

A
Hydrated Al2O3 precipitates, when CO2 is bubbled through a solution of sodium aluminate.
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B
Addition of Na3AlF6 lowers the melting point of alumina.
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C
CO2 is evolved at the anode during electrolysis
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D
The cathode is a steel vessel with a lining of carbon.
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Solution

The correct option is D The cathode is a steel vessel with a lining of carbon.
Answer: A, B, C, D
a)Extraction of aluminium (Hall's process and Hall Heroult's electrolytic cell):
The process involved in extraction of aluminium is Hall Heroult’s process. During process, Al2O3 is obtained as precipitate when CO2 is bubbled through a solution of sodium aluminate. The following reaction takes place:

2NaAlO2+CO2(g)+3H2O(l)2Al(OH)3(orAl2O3.xH2O)+Na2CO3

b) Electrolytic reduction of pure alumina takes place in steel box with lining of carbon (cathode) with cryolite(Na3AlF6) and fluorspar(CaF2) which lowers the melting point and increases the conductivity of electrolyte.

c) Electrolysis process in Hall’s process:
Graphite rods acts as anode:
At cathode: Al3++3eAl

At anode: The oxygen liberated at anode reacts with the carbon of anode to produce CO and CO2.
C+O2CO+2e

C+2O2CO2+4e

d) Here the cathode is a steel vessel with a lining of carbon.


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