Question

In the separation of $Cu^{2+}$ and $Cd^{2+}$ of Ilnd group in qualitative analysis of cations, tetrammine copper (II) sulphate and tetrammine cadmium (II) sulphate react with KCN to form the corresponding cyano complexes, which one of the following pairs of the complexes and their relative stability enables the separation of $Cu^{2+}$ and $Cd^{2+}$?

• A. $K_3[Cu(CN)_4]$: less stable and $K_2[Cd(CN)_4]$: more stable
• B. $K_3[Cu(CN)_4]$: more stable and $K_2[Cd(CN)_4]$: less stable
• C. $K_2[Cu(CN)_4]$: less stable and $K_2[Cd(CN)_4]$: more stable
• D. $K_2[Cu(CN)_4]$: more stable and $K_2[Cd(CN)_4]$: less stable

Answer 1

Answer: (B)

$K_3[Cu(CN)_4]$: more stable and $K_2[Cd(CN)_4]$: less stable

Answer 2

$K_3 (Cu(CN)_4)$ is more stable while in $K_2 [Cd(CN)_4)$ is less stable.
Here, Cu in + 1 oxidation state.