Which of the following is not correctly matched with respect to the processes involved in the extractive metallurgy of the respective metal?

A l_{2} O_{3} .2 H_{2} O \to A l

: Leaching, precipitation, calcination and electrolytic reduction (molten state)

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A g_{2} S \to A g

: Leaching and displacement method

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P b S \to P b

: Froth flotation process, roasting and self reduction

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K C l . M g C l_{2} .6 H_{2} O \to M g

: Dehydration by simple heating and electrolytic reduction in aqueous phase

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Solution

The correct option is D $K C l . M g C l_{2} .6 H_{2} O \to M g$ : Dehydration by simple heating and electrolytic reduction in aqueous phase
A) Extraction of $A l$ from its ore follows these steps:
Leaching, precipitation, calcination and electrolytic reduction (molten state)
$A l_{2} O_{3} (s) + 3 H_{2} O (l) + 2 N a O H (a q) L e a c h i n g - ---- \to 2 N a [A l (O H)_{4}] (a q)$

$2 N a [A l (O H)_{4}] (a q) + C O_{2} (g) \to A l_{2} O_{3} . x H_{2} O (s) + 2 N a H C O_{3} (a q)$

$A l_{2} O_{3} . x H_{2} O (s) 1470 K - ------ \to C a l c i n a t i o n A l_{2} O_{3} (s) + x H_{2} O (g)$

Electrolytic reduction of molten pure $A l_{2} O_{3}$ is mixed with $N a_{2} A l F_{6}$ or $C a F_{2}$

This method is known as Hall-Heroult process
$C a t h o d e : A l^{3 +} (m e l t) + 3 e^{-} \to A l (l)$

$A n o d e : C (s) + O^{2 -} (m e l t) \to C O (g) + 2 e^{-}$
$C (s) + 2 O^{2 -} (m e l t) \to C O_{2} (g) + 4 e^{-}$
B) In case of $A g$ , extraction follows leaching and displacement method as:
Leaching:
$A g_{2} S + 4 N a C N ⇌ 2 N a [A g (C N)_{2}] + N a_{2} S$
$N a_{2} S + 2 O_{2} \to N a_{2} S O_{4}$

Displacement by zinc in aqueous solution:
$2 N a [A g (C N)_{2}] + Z n \to N a_{2} [Z n (C N)_{4}] + 2 A g ↓$
C) Extraction of $C u$ follows these as:
Roasting:
$2 P b S + 3 O_{2} Δ - \to 2 P b O + 2 S O_{2}$

Self reduction:
$2 P b O + P b S \to 2 P b + S O_{2}$
D) Extraction of $M g$ follows:
Calcination:
$M g C l_{2} .6 H_{2} O Δ (c a l c i n a t i o n) - -------- \to D r y H C l (g) M g C l_{2} + 5 H_{2} O$

It is not made anhydrous by simple heating because it gets hydrolysed
$M g C l_{2} .6 H_{2} O Δ - \to M g O .5 H_{2} O + 2 H C l$

Electrolytic reduction:
Electrolytic reduction of molten anhydrous carnalite.
$M g C l_{2} ⇌ M g^{2 +} + 2 C l^{-}$

At cathode: $M g^{2 +} + 2 e^{-} \to M g$ (99% pure);

At anode: $2 C l^{-} \to C l_{2} + 2 e^{-}$
Option D represents the incorrect statement.
Ans-option D

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