Question

$\ln$ the process of extraction of gold,

Roasted gold ore + ${CN}^{-}+H_{2}O\stackrel{O_2}{⟶}\left[X\right]+{OH}^{-}$

$\left[X\right]+$ Zn $\to \left[Y\right]+$ Au

Identify the complexes [X] and [Y].

• A. $X=\left[Au\right(CN{)}_2{]}^{-},Y=\left[Zn\right(CN{)}_4{]}^{2-}$
• B. $X=\left[Au\right(CN{)}_4{]}^{3-},Y=\left[Zn\right(CN{)}_4{]}^{2-}$
• C. $X=\left[Au\right(CN{)}_2{]}^{-},Y=Zn(CN{)}_6{]}^{4-}$
• D. $X=\left[Au\right(CN{)}_4{]}^{-},Y=\left[Zn\right(CN{)}_4{]}^{2-}$

Answer 1

The correct option is A $X=\left[Au\right(CN{)}_2{]}^{-},Y=\left[Zn\right(CN{)}_4{]}^{2-}$

Au (Roasted gold ore) + ${CN}^{-}+H_{2}O\stackrel{O_2}{⟶}\left[X\right]+{OH}^{-}$

Maximum Co-ordination Number= 2 $\times$ Oxidation Number of the metal.

Therefore,${Au}^{+}$ cannot have more than 2 cyanide ions attached.

The complex X=$[Au{\left(CN\right)}_2{]}^{-}$

$[Au{\left(CN\right)}_2{]}^{-}$+ Zn → [Y] + Au

According to the photochemical series, Zn can displace Au.${Zn}^{2+}$ cannot have Co-ordination Number more than 4, and it is the only form in which Zn exists.

Hence, the complex Y=$[Zn{\left(CN\right)}_4{]}^{2-}$