JEE Main · 2021 · 24 Feb 2021 · Shift 1 · General Principles and Processes of Isolation of Metals

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Al_{2} O_{3}

was leached with alkali to get X . The solution of X on passing of gas Y , forms Z, X, Y and Z respectively are :

(A) $X = Na [Al (OH)_{4}], Y = CO_{2}, Z = Al_{2} O_{3} . \times H_{2} O$ ✓ Correct
(B) $X = Na [Al (OH)_{4}], Y = SO_{2}, Z = Al_{2} O_{3}$
(C) $X = Al (OH)_{3}, Y = SO_{2}, Z = Al_{2} O_{3} . \times H_{2} O$
(D) $X = Al (OH)_{3}, Y = CO_{2}, Z = Al_{2} O_{3}$

Answer: (A)

Solution

This question describes the Bayer process for purification of bauxite (aluminium ore).

Step 1: Leaching with alkali

Al_{2} O_{3} + 2 NaOH + 3 H_{2} O \to 2 Na [Al (OH)_{4}]

Aluminium oxide (amphoteric) reacts with sodium hydroxide to form sodium aluminate or sodium tetrahydroxoaluminate(III), which is X.

Step 2: Passing CO₂ gas

Na [Al (OH)_{4}] + CO_{2} \to Al (OH)_{3} ↓ + NaHCO_{3}

or more generally:

Na [Al (OH)_{4}] CO_{2} Al_{2} O_{3} \cdot x H_{2} O

Carbon dioxide (gas Y) is passed through the sodium aluminate solution, which precipitates hydrated alumina, Z =

Al_{2} O_{3} \cdot x H_{2} O

(or Al(OH)₃).

Therefore:

X = Na[Al(OH)₄] (sodium aluminate)
Y = CO₂ (carbon dioxide)
Z = Al₂O₃·xH₂O (hydrated alumina)

JEE Main · 2021 · 24 Feb 2021 · Shift 1 · Single correct option

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JEE Main · 2021 · 24 Feb 2021 · Shift 1 · General Principles and Processes of Isolation of Metals

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