Question

From the stability constant ( hypothetical values ), given below, predict which is the strongest ligand?

• A. $C{u}^{2+}+4N{H}_3\rightleftharpoons {\left[Cu{\left(N{H}_3\right)}_4\right]}^{2+},K=4.5\times {10}^{11}$
• B. $C{u}^{2+}+4C{N}^{-}\rightleftharpoons {\left[Cu{\left(CN\right)}_4\right]}^{2-},K=2.0\times {10}^{27}$
• C. $C{u}^{2+}+2en\rightleftharpoons {\left[Cu{\left(en\right)}_2\right]}^{2+},K=3.0\times {10}^{15}$
• D. $C{u}^{2+}+4H_{2}O\rightleftharpoons {\left[Cu{\left(H_{2}O\right)}_4\right]}^{2+},K=9.5\times {10}^8$

Answer 1

The correct option is B $C{u}^{2+}+4C{N}^{-}\rightleftharpoons {\left[Cu{\left(CN\right)}_4\right]}^{2-},K=2.0\times {10}^{27}$

A stability constant is an equilibrium constant for the formation of a complex in solution. It is a measure of the strength of the interaction between the reagents that come together to form the complex.
As $C{u}^{2+}+4C{N}^{-}\rightleftharpoons {\left[Cu{\left(CN\right)}_4\right]}^{2-},K=2.0\times {10}^{27}$ has maximum value of stability constant so $C{N}^{-}$ is strongest ligand.