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  • The following reaction takes place during the process of extraction of gold:   Roasted gold ore <img alt="+\mathrm{CN}^{-}+\mathrm{O}_2+2 \mathrm{H}_2 \mathrm{O} \rightarro

The following reaction takes place during the process of extraction of gold: 

 Roasted gold ore +\mathrm{CN}^{-}+\mathrm{O}_2+2 \mathrm{H}_2 \mathrm{O} \rightarrow[\mathrm{X}]+\mathrm{OH}^{-}

[\mathrm{X}]+\mathrm{Zn} \rightarrow[\mathrm{Y}]+\mathrm{Au}

Identify the compounds [X] and [Y].

Option: 1

\begin{array}{ll} {[\mathrm{X}]=\left[\mathrm{Au}(\mathrm{CN})_4\right],} {[\mathrm{Y}]=\left[\mathrm{Zn}(\mathrm{CN})_6\right]^{2-}} \\ \end{array}


Option: 2

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


Option: 3

{[\mathrm{X}]=\left[\mathrm{Au}(\mathrm{CN})_4\right]^{3-}, \quad[\mathrm{Y}]=\left[\mathrm{Zn}(\mathrm{CN})_4\right]^{2-}} \\


Option: 4

{[\mathrm{X}]=\left[\mathrm{Au}(\mathrm{CN})_2\right]^{-}, \quad[\mathrm{Y}]=\left[\mathrm{Zn}(\mathrm{CN})_6\right]^{4-}}


Answers (1)

best_answer

In the metallurgy of silver and of gold, the respective metal is leached with a dilute solution of  \text{NaCN or KCN } in the presence of air (for \text{O}_{2}) from which the metal is obtained later by replacement.

4 Roasted gold ore +8 \mathrm{CN}^{-}+\mathrm{O}_{2(\mathrm{~g})}+2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{aq})} \rightarrow\left[\mathrm{Au}(\mathrm{CN})_2\right]_{(\mathrm{aq})}^{-}+4 \mathrm{OH}_{(\mathrm{aq})}^{-}

\begin{aligned} & 2\left[\mathrm{Au}(\mathrm{CN})_2\right]_{(\mathrm{aq})}^{-}+\mathrm{Zn}_{(\mathrm{s})} \rightarrow\left[\mathrm{Zn}(\mathrm{CN})_4\right]_{(\mathrm{aq})}^{2-}+2 \mathrm{Au}_{(\mathrm{s})} \\ \\& \text { Hence, }[\mathrm{X}]=\left[\mathrm{Au}(\mathrm{CN})_2\right]^{-}, \quad[\mathrm{Y}]=\left[\mathrm{Zn}(\mathrm{CN})_4\right]^{2-} \end{aligned}

Posted by

Sanket Gandhi

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