JEE Advanced 2021 Paper 1 Q15 Chemistry Inorganic Chemistry Metallurgy Medium

JEE Advanced 2021 Paper 1 · Q15 · Metallurgy

The correct statement(s) related to the metal extraction processes is(are):

  1. A. A mixture of PbS and PbO undergoes self-reduction to produce Pb and SO$_2$.
  2. B. In the extraction process of copper from copper pyrites, silica is added to produce copper silicate.
  3. C. Partial oxidation of sulphide ore of copper by roasting, followed by self-reduction produces blister copper.
  4. D. In cyanide process, zinc powder is utilized to precipitate gold from Na[Au(CN)$_2$].
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:A, C, D

Solution

(A) Correct. After partial roasting of galena, PbS reacts with PbO in a self-reduction (auto-reduction): PbS + 2 PbO → 3 Pb + SO$_2$. This is the standard metallurgical route for lead from galena.

(B) Wrong. In the extraction of Cu from copper pyrite (CuFeS$_2$), silica (SiO$_2$) is added during smelting to combine with FeO (the impurity formed on roasting) to give iron silicate slag FeSiO$_3$. SiO$_2$ is NOT added to make copper silicate; the Cu is recovered as matte (Cu$_2$S · FeS) and later as metallic Cu.

(C) Correct. Roasting CuFeS$_2$ partially oxidises sulphide to Cu$_2$S + FeS + SO$_2$; the resulting concentrate (matte) then undergoes self-reduction in a Bessemer-type converter: Cu$_2$S + 2 Cu$_2$O → 6 Cu + SO$_2$, giving impure 'blister' copper.

(D) Correct. In the Macarthur-Forrest cyanide process for gold, gold is dissolved as [Au(CN)$_2$]$^-$ and then displaced by zinc dust: 2 Na[Au(CN)$_2$] + Zn → Na$_2$[Zn(CN)$_4$] + 2 Au↓.

Hence (A), (C) and (D) are correct.

Want to drill deeper? Open this question inside SolveKar AI and tap "Why?" on any step — the AI Mentor reads your full solution context and explains until it clicks. Download SolveKar AI →