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Electrolytic Reduction of Alumina
Concepts tested here
- Stoichiometry of the Hall-Heroult process
All Questions
2005 AIPMT 1 question
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The mass of carbon anode consumed (giving only carbon dioxide) in the production of 270 kg of aluminium metal from bauxite by the Hall process is :-
(Atomic mass : Al = 27)In the Hall-Heroult process, alumina dissolved in molten cryolite is electrolysed; the oxygen liberated at the carbon anode burns the anode to $CO_2$.
Overall reaction: $2Al_2O_3 + 3C \rightarrow 4Al + 3CO_2$
So 4 moles of Al are produced for every 3 moles of carbon consumed.
Moles of Al in 270 kg $= \dfrac{270 \times 1000}{27} = 10000$ mol (10 kmol)
Moles of carbon consumed $= \dfrac{3}{4} \times 10000 = 7500$ mol
Mass of carbon $= 7500 \times 12 = 90000$ g
$= 90$ kg