JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 · General Principles and Processes of Isolation of Metals

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

(A)Hydrated $Al_{2} O_{3}$ precipitates, when $CO_{2}$ is bubbled through a solution of sodium aluminate.✓ Correct
(B)Addition of $Na_{3} AlF_{6}$ lowers the melting point of alumina.✓ Correct
(C) $CO_{2}$ is evolved at the anode during electrolysis.✓ Correct
(D)The cathode is a steel vessel with a lining of carbon.✓ Correct

Answer: (A), (B), (C), (D)

Solution

(A) When

CO_{2}

is bubbled through sodium aluminate solution:

2 Na [Al (OH)_{4}]_{(aq.)} + CO_{2} ⟶ Na_{2} CO_{3} + H_{2} O + 2 Al (OH)_{3} (↓)

Hydrated alumina precipitates. ✓

(B)

Na_{3} AlF_{6}

(cryolite) is added to lower the melting point of

Al_{2} O_{3}

from ~2000°C to ~900°C. ✓

(C) During electrolysis, at the anode (graphite):

2 O^{2 -} ⟶ O_{2} + 4 e^{-}

C + O_{2} ⟶ CO (↑) + CO_{2} (↑)

CO_{2}

is evolved. ✓

(D) The cathode is a steel vessel lined with carbon. ✓

All statements are correct.

JEE Advanced · 2020 · 27 Sep 2020 · Paper 2 · One or more correct options