Question

Complexes formed in the cyanide process are:

• A. $\left[Au\right(CN{)}_2{]}^{-}$
• B. $\left[Ag\right(CN{)}_2{]}^{-}$
• C. $\left[Au\right(CN{)}_4{]}^{2-}$
• D. $\left[Zn\right(CN{)}_4{]}^{2-}$

Answer 1

Answer: (A), (B), (D)

$\left[Zn\right(CN{)}_4{]}^{2-}$

Siver is extracted from its ore - argentite $\left(A{g}_{2}S\right)$, using the cyanide process. Reacting the ore with $NaCN$ forms $Na\left[Ag\right(CN{)}_2]$
$AgS+4NaCN\to 2\mathrm{Na}\left[\mathrm{Ag}\right(\mathrm{CN}{)}_2]+{\mathrm{Na}}_{2}S$

$Na\left[Ag\right(CN{)}_2]$ combines with zinc dust to form $N{a}_2\left[Zn\right(CN{)}_4]$
$\mathrm{Zn}+2\mathrm{Na}\left[\mathrm{Ag}\right(\mathrm{CN}{)}_2]\to {\mathrm{Na}}_2[\mathrm{Zn}\left(\mathrm{CN}{)}_4\right]+2\mathrm{Ag}$
Gold reacts with $NaCN$ to form $\left[Au\right(CN{)}_2{]}^{-}$ :
$4Au+8NaCN+O_2+2H_{2}O\to 4Na\left[Au\right(CN{)}_2]+4NaOH$