Question

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

• A. The $△G_f^0$ of the sulphide is greater than those for $C{S}_2$ and $H_{2}S$.
• B. The $△G_f^0$ 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

The correct option is D Carbon and hydrogen are suitable reducing agents for metal sulphides.

The standard free energies of formation ($△G_f^0$) of most of the sulphides are more negative than those of $C{S}_2$ and $H_{2}S$. Hence, neither carbon nor hydrogen can reduce metal sulphides to metal. The standard free energies of formation of oxides are much lower than those of $S{O}_2$. Therefore, oxidation of metal oxides is thermodynamically favourable. Hence sulphide is thermodynamically favourable. Hence sulphide ore is roasted to the oxide before reduction.