Question

Out of $\left[Cu\right(CN{)}_4{]}^{3-}$ and $\left[Cd\right(CN{)}_4{]}^{2-}$, $\left[Cu\right(CN{)}_2{]}^{3-}$ is unstable and gives black precipitate of $CuS$ on passing $H_{2}S$ gas.
If true 1 else 0.

• A. 0

Answer 1

The correct option is A 0

$2C{u}^2+4C{N}^{-}\to 2C{u}^{1}CN+(CN{)}_2$ Cyanogen.

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

${\left[Cu\right(CN{)}_4]}^{3-}$ is a stable complex. $C{d}^{2+}$ also forms complex $\left[Cd\right(CN{)}_4{]}^{2-}$ But unstable, which ionises to form $C{d}^{2+}$ and $C{N}^{-}$. Thus if $C{d}^{2+}$ and $C{u}^{2+}$ both are present, $C{u}^{2+}$ and $C{d}^{2+}$ both are complexed by $C{N}^{-}$. If $H_{2}S$ gas is passed, $C{d}^{2+}$ ( in unstable $\left[Cd\right(CN{)}_4{)}^{2-}\left]\right)$gives yellow precipitate of Cds.