Question

Which of the following complexes formed by \[\ce{Cu^2+}\] ions is most stable?

Options

• \[\ce{Cu^{2+} + 4NH3 ⇌ [Cu(NH3)4]^{2+}, logK = 11.6}\]

• \[\ce{Cu^{2+} + 4CN^- ⇌ [Cu(CN)4]^{2-}, logK = 27.3}\]

• \[\ce{Cu^{2+} + 2en ⇌ [Cu(en)2]^{2+}, logK = 15.4}\]

• \[\ce{Cu^{2+} + 4H2O ⇌ [Cu(H2O)4]^{2+}, logK = 8.9}\]

Answer 1

\[\ce{Cu^{2+} + 4CN^- ⇌ [Cu(CN)4]^{2-}, logK = 27.3}\]

Explanation:

The greater the value of log K, the greater will be stability of complex compound formed.

For reaction,

\[\ce{Cu^{2+} + 4CN^{-} -> [Cu(CN)4]^{2-}}\]

`"K" = (["Cu"(("CN")_4)^(2-)])/(["Cu"^(2+)]["CN"^(-)]^4)` and log K = 27.3

For this reaction, log K has highest value among the given four reactions. Hence, K will also be higher among these four, i.e., stability of the complexes will be highest among these four complexes.