Question

Which of the following complexes formed by $C{u}^{2+}$ ions is most stable?

• A. $C{u}^{2+}+4N{H}_3\rightleftharpoons \left[Cu\right(N{H}_3{)}_4{]}^{2+},logK=11.6$
• B. $C{u}^{2+}+4C{N}^{-}\rightleftharpoons \left[Cu\right(CN{)}_4{]}^{2-},logK=27.3$
• C. $C{u}^{2+}+2en\rightleftharpoons \left[Cu\right(en{)}_2{]}^{2+},logK=15.4$
• D. $C{u}^{2+}+4H_{2}O\rightleftharpoons \left[Cu\right(H_{2}O{)}_4{]}^{2+},logK=8.9$

Answer 1

The correct option is B $C{u}^{2+}+4C{N}^{-}\rightleftharpoons \left[Cu\right(CN{)}_4{]}^{2-},logK=27.3$

Higher the value of stability constant K, greater is the stability. In the given examples, option (B) gives the reaction with the highest value of log K which in turn corresponds to the highest value of K. So $\left[Cu\right(CN{)}_4{]}^{2-}$ is most stable out of given $C{u}^{2+}$ complexes.