Q. During the extraction of gold the following reactions take place $Au + {CN}^{-} + H_{2}O\overset{O_{2}}{\rightarrow}\lbrack X\rbrack$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \lbrack X\rbrack + Zn \longrightarrow \lbrack Y\rbrack + Au\$ $X$ and $Y$ are respectively
A) $\left\lbrack Au(CN)_{2} \right\rbrack^{-}and\ \left\lbrack Zn(CN)_{6} \right\rbrack^{4 -}$
B) $\left\lbrack Au(CN)_{4} \right\rbrack^{2 -}and\ \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
C) $\left\lbrack Au(CN)_{4} \right\rbrack^{3 -}and\ \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
D) $\left\lbrack Au(CN)_{2} \right\rbrack^{-}and\ \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
Explanation
(d)
$4Au + 8{CN}^{-} + 2H_{2}O + O_{2}\ \longrightarrow 4\left\lbrack Au(CN)_{2} \right\rbrack^{-}\ + 4{OH}^{-}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ soluble$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 2\left\lbrack Au(CN)_{2} \right\rbrack^{-} + Zn\ \longrightarrow 2Au(s) \downarrow + \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.