General Principles and Processes of Isolation of Elements - Result Question 13
####13. Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?
[2007]
(a) The $\Delta G_f^{0}$ of the sulphide is greater than those for $CS_2$ and $H_2 S$.
(b) The $\Delta G_f^{0}$ 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.
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Solution:
- (d) 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 $H_2 S$, 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.
