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Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true ?
The $\Delta G_f^o$ of the sulphide is greater than those for $CS_2$ and $H_2S.$
The $\Delta G_f^o$ is negative for roasting of sulphide ore to oxide.
Roasting of the sulphide to the oxide is thermodynamically feasible.
Carbon and hydrogen are suitable reducing agents for metal sulphides.
Solution
The standard free energies of formation $\left(\Delta G_{f}^{o}\right)$ of most of the sulphides are greater than those of $\mathrm{CS}_{2}$ and $\mathrm{H}_{2} \mathrm{S}$. 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 $\mathrm{SO}_{2}$. Therefore, oxidation of metal sulphides to metal oxides is thermodynarnically Favourable. Hence sulphide ore is roasted to the oxide before reduction.
