Question

When KCN is added to $CuS{O}_4$ solution:

• A. KCN acts an reducing agent.
• B. KCN acts as an complexing agent.
• C. $K_3\left[Cu\right(CN{)}_4]$ is formed.
• D. All are correct.

Answer 1

The correct option is D All are correct.

Addition of $KCN$ to $CuS{o}_4$ sollution first causes reductiion and then precipitates $CuCN$ (curprous cyanide )

This reacts with excess$C{N}^{-}$forming a soluble four co-ordinate compledx $\left[Cu\right(CN{)}_4{]}^{3-}$ which is tetrahedral in shape :

$2C{u}^{2+}+4C{N}^{-}\to 2C{u}^{I}CN+\underset{Cyanogen}{(CN{)}_2}$

$CuCN+3C{N}^{-}\to \underset{colourlesscomplex}{\left[C{u}^I\right(CN{)}_4{]}^{3-}}$