Q. In the process of extraction of gold, Roasted gold ore $+ {CN}^{-}\ + \ H_{2}O\ \overset{O_{2}}{\rightarrow}\ \lbrack X\rbrack\ + \ {OH}^{-}$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \lbrack X\rbrack\ + \ Zn\ \longrightarrow \ \lbrack Y\rbrack\ + \ Au$ Identify the complexes [$X$] and [$Y$]
A) $X = \left\lbrack Au(CN)_{2} \right\rbrack^{-},\ Y = \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
B) $X = \left\lbrack Au(CN)_{4} \right\rbrack^{3 -},\ Y = \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
C) $X = \left\lbrack Au(CN)_{2} \right\rbrack^{-},\ Y = \left\lbrack Zn(CN)_{6} \right\rbrack^{4 -}$
D) $X = \left\lbrack Au(CN)_{4} \right\rbrack^{-},\ Y = \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
Explanation
(a)
$Au + 4{CN}^{-} + H_{2}O\ + \frac{1}{2}O_{2} \longrightarrow 2\lbrack Au{\left( {CN}_{2} \right)\rbrack}^{-} + 2{OH}^{-}$
$\mathbf{From\ gold}$ ore ($\mathbf{X}$)
$2\left\lbrack Au(CN)_{2} \right\rbrack^{-} + Zn \longrightarrow \left\lbrack Zn(CN)_{2} \right\rbrack^{-} + 2Au$
$(X)$
$Hence,\lbrack X\rbrack = \left\lbrack \ Au(CN)_{2} \right\rbrack^{-},Y = \left\lbrack Zn(CN)_{4} \right\rbrack^{2 -}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.