Verified Solution • 2025–26 Session moderate

QJEEAdv20Ch14e2: JEE Advanced 2020 Chemistry - Class 12 JEEAdv20Ch14e2 Solution: Which among the following statement(s) is/are true for the…

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

Multiple Choice Options

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

Step-by-Step Verified Solution

2Na[Al(OH)4](aq)+CO2⟶Na2CO3+H2O+2Al(OH)3↓or Al2O3 . 2H2O(ppt.)2Na[Al{(OH)_4}](aq) + C{O_2}\mathrel{\mathop{\kern0pt\longrightarrow}\limits_{}} N{a_2}C{O_3} + {H_2}O + 2Al{(OH)_3} \downarrow or\,A{l_2}{O_3}\,.\,2{H_2}O (ppt.)

Hence, the statement (a) is true.

(b) The electrolysis of alumina by Hall-Heroult's process is carried by using a fused mixture of alumina and cryolite (Na2AlF6) along with minor quantities of aluminium fluoride and fluorspar. The addition of cryolite and fluorspar increases the electrical conductivity of alumina and lowers the fusion temperature. Hence, the statement (b) is true.

(c) At anode, alumina reacts with fluorine to liberate oxygen and evolved oxygen reacts with carbon to form carbon dioxide and hence, statement (c) is true.

(d) Steel cathode with carbon lining and graphite anode are used and hence, the statement (d) is true.

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