JEE Challenger
More from General Principles and Processes of Isolation of Elements
ChemMedAdv 2021 • Paper 1

Identify Correct Statements on Metal Extraction Processes

Select the correct statement(s) pertaining to metal extraction processes:

Options

A

A mixture of PbS\text{PbS} and PbO\text{PbO} undergoes self-reduction to produce Pb\text{Pb} and SO2\text{SO}_2.

Correct
B

In the extraction process of copper from copper pyrites, silica is added to produce copper silicate.

C

Partial oxidation of sulphide ore of copper by roasting, followed by self-reduction produces blister copper.

Correct
D

In cyanide process, zinc powder is utilized to precipitate gold from Na[Au(CN)2]\text{Na}[\text{Au}(\text{CN})_2].

Correct

Topics & Concepts

General Principles and Processes of Isolation of ElementsMetallurgy

Step-by-Step Solution

To determine the correct statements regarding metal extraction processes, let us analyze each option step-by-step:

  1. Analysis of Option (A): In the metallurgy of lead, galena (PbS\text{PbS}) undergoes partial roasting in air to form lead oxide (PbO\text{PbO}) and lead sulphate (PbSO4\text{PbSO}_4). On further heating in the absence of air, the unreacted PbS\text{PbS} reacts with PbO\text{PbO} (and PbSO4\text{PbSO}_4) in a self-reduction (auto-reduction) reaction to yield metallic lead: PbS+2PbO⟶3Pb+SO2↑\text{PbS} + 2\text{PbO} \longrightarrow 3\text{Pb} + \text{SO}_2 \uparrow Hence, statement (A) is correct.

  2. Analysis of Option (B): In the extraction of copper from copper pyrites (CuFeS2\text{CuFeS}_2), silica (SiO2\text{SiO}_2) is added as an acidic flux. It reacts with iron oxide (FeO\text{FeO}), which is a basic impurity, to form iron silicate slag (FeSiO3\text{FeSiO}_3): FeO+SiO2⟶FeSiO3(slag)\text{FeO} + \text{SiO}_2 \longrightarrow \text{FeSiO}_3 \quad (\text{slag}) It does not form copper silicate. Hence, statement (B) is incorrect.

  3. Analysis of Option (C): During the extraction of copper from copper matte (Cu2S+FeS\text{Cu}_2\text{S} + \text{FeS}), partial roasting converts a portion of cuprous sulphide (Cu2S\text{Cu}_2\text{S}) into cuprous oxide (Cu2O\text{Cu}_2\text{O}): 2Cu2S+3O2⟶2Cu2O+2SO22\text{Cu}_2\text{S} + 3\text{O}_2 \longrightarrow 2\text{Cu}_2\text{O} + 2\text{SO}_2 This is followed by self-reduction: Cu2S+2Cu2O⟶6Cu+SO2↑\text{Cu}_2\text{S} + 2\text{Cu}_2\text{O} \longrightarrow 6\text{Cu} + \text{SO}_2 \uparrow As molten copper solidifies, the escaping SO2\text{SO}_2 gas gives it a blistered appearance, forming blister copper. Hence, statement (C) is correct.

  4. Analysis of Option (D): In the MacArthur-Forrest cyanide process for the extraction of gold, gold is leached as a soluble complex Na[Au(CN)2]\text{Na}[\text{Au}(\text{CN})_2]. Zinc powder is then added as a more electropositive metal to displace and precipitate metallic gold via a redox reaction: 2Na[Au(CN)2]+Zn⟶Na2[Zn(CN)4]+2Au↓2\text{Na}[\text{Au}(\text{CN})_2] + \text{Zn} \longrightarrow \text{Na}_2[\text{Zn}(\text{CN})_4] + 2\text{Au} \downarrow Hence, statement (D) is correct.

Conclusion: The correct statements are A, C, and D.

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