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In the extraction of silver, zinc metal is used as a reducing agent. What is the molecular structure of the zinc complex formed in this reaction?
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The correct answer is:
Tetrahedral
During extraction of silver, the finely powdered silver ore is treated with dilute KCN solution to form a cyano complex of silver. This complex is water soluble.
\(\mathrm{Ag}_2 \mathrm{~S}+4 \mathrm{NaCN} \rightleftharpoons 2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_2\right]+\mathrm{Na}_2 \mathrm{~S}\)
Then zinc is added to the solution. More electropositive zinc displaces silver from the complex.
\(\left.2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_2\right]+\mathrm{Zn} \longrightarrow \mathrm{Na}_2\left[\mathrm{Zn}(\mathrm{CN})_4\right)+2 \mathrm{Ag}\right]\)
In \(\mathrm{Zn}(\mathrm{CN})_2\), zinc adopts the tetrahedral coordination environment, all linked by bridging cyanide ligands.
Hence, the correct option is (a).
\(\mathrm{Ag}_2 \mathrm{~S}+4 \mathrm{NaCN} \rightleftharpoons 2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_2\right]+\mathrm{Na}_2 \mathrm{~S}\)
Then zinc is added to the solution. More electropositive zinc displaces silver from the complex.
\(\left.2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_2\right]+\mathrm{Zn} \longrightarrow \mathrm{Na}_2\left[\mathrm{Zn}(\mathrm{CN})_4\right)+2 \mathrm{Ag}\right]\)
In \(\mathrm{Zn}(\mathrm{CN})_2\), zinc adopts the tetrahedral coordination environment, all linked by bridging cyanide ligands.
Hence, the correct option is (a).
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