Which of the following reduction reactions are actually employed in the commercial extraction of metals?

F e_{2} O_{3} + 2 A l \to A l_{2} O_{3} + 2 F e

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C r_{2} O_{3} + 2 A l \to A l_{2} O_{3} + 2 C r

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2 N a [A u (C N)_{2}] + Z n \to N a_{2} [Z n (C N)_{4}] + 2 A u

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C u_{2} O + H_{2} \to 2 C u + H_{2} O

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Solution

The correct options are
B $C r_{2} O_{3} + 2 A l \to A l_{2} O_{3} + 2 C r$
C $2 N a [A u (C N)_{2}] + Z n \to N a_{2} [Z n (C N)_{4}] + 2 A u$
(a) Iron is commercially extracted by reduction with $C$ and $C O$ . Thus (a) is incorrect.

(b) Chromium is extracted commercially by reduction with aluminium.

(c) Leaching of $A u_{2} S$ is carried out by heating it with a dilute solution of $N a C N$ in the presence of $O_{2}$ .
$A u_{2} S + 4 N a C N ⟶ 2 N a [A u (C N)_{2}] + N a_{2} S$

Treatment of the cyanide compound with zinc takes place via displacement reaction.
$2 N a [A u (C N)_{2}] + Z n \to N a_{2} [Z n (C N)_{4}] + 2 A u$

(d) The commercial metallurgical process for the extraction of metallic copper from its sulphide ore involves the oxidation of $C u_{2} S$ to $C u_{2} O$ and the auto-reduction of a mixture of $C u_{2} S$ and $C u_{2} O$ to copper metal.
Thus, (d) is incorrect.

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10 g

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2 A l + F e_{2} O_{3} \to A l_{2} O_{3} + 2 F e

A l_{2} O_{3}

C r_{2} O_{3}

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- 1676 k J

- 1141 k J

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4 A u + 8 C N^{-} + 2 H_{2} O + O_{2} \to 4 [A u (C N)_{2}]^{-} + 4 O H^{-}

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2 A l (s) + 1 \frac{1}{2} O_{2} (g) ⟶ A l_{2} O_{3} (s), Δ H = - 166.78 k J

H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ H_{2} O (l), Δ H = - 285.9 k J

Δ H

A l_{2} O_{3} (s) ⟶ 2 A l (s) + 1 \frac{1}{2} O_{2} (g)

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