Question

The metal extracted by leaching with a cyanide is:

• A. Mg
• B. Ag
• C. Cu
• D. Na

Answer 1

Answer: (B)

Ag

Leaching is often used if the ore is soluble in some suitable solvent. In the metallurgy of silver and that of gold, the respective metal is leached with a dilute solution of NaCN or KCN in the presence of air (for $O_2$) from which the metal is obtained later by replacement.

$4M\left(s\right)+8C{N}^{-}\left(aq\right)+2H_{2}O\left(aq\right)+O_2\left(g\right)\to 4\left[M\right(CN{)}_2{]}^{-}\left(aq\right)+4O{H}^{-}\left(aq\right)$ (M = Ag or Au)

$2\left[M\right(CN{)}_2{]}^{-}\left(aq\right)+Zn\left(s\right)\to \left[Zn\right(CN{)}_4{]}^{2-}\left(aq\right)+2M\left(s\right)$

Hence, option B is correct.