Extraction of Metals - Result Question 23
####23. In the cyanide extraction process of silver from argentite ore, the oxidising and reducing agents used are
(2012)
(a) $O _2$ and $CO$ respectively
(b) $O _2$ and $Zn$ dust respectively
(c) $HNO _3$ and $Zn$ dust respectively
(d) $HNO _3$ and $CO$ respectively
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Solution:
- The reactions involved in extraction of silver by cyanide process are
$$ \begin{aligned} & Ag _2 S+CN^{-}+O _2 \longrightarrow\left[Ag(CN) _2\right]^{-}+SO _2 \ & {\left[Ag(CN) _2\right]+Zn \longrightarrow\left[Zn(CN) _4\right]^{2-}+Ag} \end{aligned} $$
In reaction (i), sulphide is oxidised to $SO _2$ by oxygen. In the reaction (ii), silver ion $\left(Ag^{+}\right)$is reduced to $Ag$ by $Zn$. Therefore, $O _2$ is oxidising agent and $Zn$ is reducing agent.
