JEE Advanced 2020 · Paper 2 · Chemistry Q9

ChemistryMultiple correct+4 / -2Question 27 of 54

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

Hydrated

\ce{Al2O3}

precipitates, when

\ce{CO2}

is bubbled through a solution of sodium aluminate.

Addition of

\ce{Na3AlF6}

lowers the melting point of alumina.

\ce{CO2}

is evolved at the anode during electrolysis.

The cathode is a steel vessel with a lining of carbon.

Answer and worked solution

Official answer: A, B, C, D

(A) In the Bayer process, $\ce{CO2}$ passed into sodium aluminate solution precipitates hydrated alumina: $\ce{2Na[Al(OH)4] + CO2 -> Al2O3.xH2O + Na2CO3}$ . True.
(B) Cryolite, $\ce{Na3AlF6}$ , lowers the melting point of the electrolyte (to about 1250 K) and improves its conductivity. True.
(C) The carbon anodes are oxidised by the oxygen released, giving $\ce{CO}$ and $\ce{CO2}$ . True.
(D) The cell is a steel vessel lined with carbon, which acts as the cathode. True.

(A), (B), (C), (D)

Topics:Extraction of specific metals Concentration of ores

JEE Advanced 2020 · Paper 2, Chemistry question 9