Question

If $C{u}^{2+}$ and $C{d}^{2+}$ both are present, it is difficult to analyse. A scheme to analyse in a mixture is given below.
KCN forms complex with $C{u}^{2+}$ and $C{d}^{2+}$
$C{u}^{2+}+2C{N}^{-}⟶Cu(CN{)}_2$
$Cu(CN{)}_2⟶2CuCN\downarrow +(CN{)}_2$
$CuCN+3KCN{K}_3\underset{stable}{Cu\left(CN{)}_4\right]}C{d}^{2+}+KCN⟶K_2\underset{unstable}{\left[Cd\right(CN{)}_4]}$
when $H_{2}S$ gas is passed, unstable complex of $C{d}^{2+}$ gives yellow ppt
$\left[Cd\right(CN{)}_4{]}^{2-}\rightleftharpoons C{d}^{2+}+4C{N}^{-}$
$C{d}^{2+}+S^{2-}⟶\underset{yellow}{CdS}\downarrow$
If true enter 1, else enter 0.

Answer 1

Both $C{u}^{2+}$ and $C{d}^{2+}$ ions react with KCN to form complex.
$C{u}^{2+}+2C{N}^{-}⟶Cu(CN{)}_2$
$Cu(CN{)}_2⟶2CuCN\downarrow +(CN{)}_2$
$CuCN+3KCN{K}_3\underset{stable}{Cu\left(CN{)}_4\right]}$
$C{d}^{2+}+KCN⟶K_2\underset{unstable}{\left[Cd\right(CN{)}_4]}$
The complex of copper is stable but the complex of cadmium is unstable.
When $H_{2}S$ gas is passed, unstable complex of $C{d}^{2+}$ gives yellow precipitate.
$\left[Cd\right(CN{)}_4{]}^{2-}\rightleftharpoons C{d}^{2+}+4C{N}^{-}$
$C{d}^{2+}+S^{2-}⟶\underset{yellow}{CdS}\downarrow$
No such precipitate is obtained with complex of copper.