In the extraction of silver by the Mac-Arthur | vedclass

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(D) In the extraction of silver from argentite ore $(Ag_2S)$,the ore is treated with a dilute solution of $NaCN$ or $KCN$ in the presence of air to fo

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to oxidise the sulphur in the argentite ore to $SO_2$ which escapes from the reaction

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(D) In the extraction of silver from argentite ore $(Ag_2S)$,the ore is treated with a dilute solution of $NaCN$ or $KCN$ in the presence of air to form a soluble complex,$Na[Ag(CN)_2]$.$Ag_2S + 4NaCN \rightarrow 2Na[Ag(CN)_2] + Na_2S$.$KNO_3$ is added as a flux to oxidise the $Na_2S$ (or $S^{2-}$ ions) formed during the reaction to $SO_2$ or $SO_4^{2-}$,preventing the reverse reaction of the complex formation.Specifically,it oxidises the sulphur impurities present in the ore to $SO_2$ which escapes,thereby shifting the equilibrium forward.

In the extraction of silver by the Mac-Arthur-Forrest cyanide process,a small amount of $KNO_3$ is also added as a flux. The function of $KNO_3$ is

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