Question

Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?

• A. The $\Delta G^{\circ}_f$ of the sulphide is greater than those for $CS_2$ and $H_2S$.
• B. The $\Delta G_f^{\circ}$ is negative for roasting of sulphide ore to oxide.
• C. Roasting of the sulphide to the oxide is thermodynamically feasible.
• D. Carbon and hydrogen are suitable reducing agents for metal sulphides.

Answer 1

Answer: (D)

Carbon and hydrogen are suitable reducing agents for metal sulphides.

Answer 2

The sulphide ore is roasted to oxide before reduction because the $\Delta G_f^{\circ}$ of most of the sulphides are greater than those of $CS_2$ and $H_2S$, therefore neither C nor H can reduce metal sulphide to metal. Further, the standard free energies of formation of oxide are much less than those of $SO_2$. Hence oxidation of metal sulphides to metal oxide is thermodynamically favourable.