Olympiad workbook

Exam: Olympiad workbook
Subject: NSEC
Chapter: General Principles and Processes of Isolation of Metals

Olympiad workbook · NSEC · General Principles and Processes of Isolation of Metals

During extraction of gold, the gold ore is treated with aqueous KCN...

During extraction of gold, the gold ore is treated with aqueous KCN solution as shown by the equations (not balanced) below to get compound X which is further reduced by Zn to obtain compound Y and metallic gold. Identify X and Y .

\begin{aligned} & \text { Gold ore }+\mathrm{CN}^{-}+\mathrm{H}_2 \mathrm{O}+\mathrm{O}_2 \rightarrow[\mathrm{X}]+\mathrm{OH}^{-} \ldots \ldots \text{(i)}\\ & {[\mathrm{X}]+\mathrm{Zn} \rightarrow[\mathrm{Y}]+\mathrm{Au}} \qquad \qquad \qquad \qquad \qquad \ldots \ldots \text{(ii)} \end{aligned}

Options

A $\mathrm{X}=$ \left[\mathrm{Au}(\mathrm{CN})_2\right]^{-}, \quad \mathrm{Y}= $\left[\mathrm{Zn}(\mathrm{CN})_2\right]^{2-}$
B $\mathrm{X}=$ \left[\mathrm{Au}(\mathrm{CN})_2\right]^{-}, \quad \mathrm{Y}= $\left[\mathrm{Zn}(\mathrm{CN})_4\right]^{2-}$
C $\mathrm{X}=$ \left[\mathrm{Au}(\mathrm{CN})_4\right]^{3-}, \mathrm{Y}= $\left[\mathrm{Zn}(\mathrm{CN})_4\right]^{2-}$
D $\mathrm{X}=$ \left[\mathrm{Au}(\mathrm{CN})_2\right], \quad \mathrm{Y}= $\left[\mathrm{Zn}(\mathrm{CN})_4\right]^{4-}$

Correct answer

B. $\mathrm{X}=$ \left[\mathrm{Au}(\mathrm{CN})_2\right]^{-}, \quad \mathrm{Y}= $\left[\mathrm{Zn}(\mathrm{CN})_4\right]^{2-}$

Step-by-step solution

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