Question

Stability constants of $\left[Cd\right(CN{)}_6{]}^{2-}$ and $\left[Ni\right(CN{)}_4{]}^{2-}$ are $1.28\times {10}^{17}$ and $1.0\times {10}^{31}$ respectively. Which is more stable?

• A. $\left[Ni\right(CN{)}_4{]}^{2-}$
• B. $\left[Cd\right(CN{)}_6{]}^{2-}$
• C. Both are equally stable
• D. None of the above

Answer 1

The correct option is A $\left[Ni\right(CN{)}_4{]}^{2-}$

The stability of a complex in solution refers to the degree of association between the two species involved in the state of equilibrium. The magnitude of the (stability or formation) equilibrium constant for the association, quantitatively expresses the stability. Since the stability constant for $\left[Ni\right(CN{)}_4{]}^{2-}$ is greater than $\left[Cd\right(CN{)}_6{]}^{2-}$ the former complex will be more stable than the later one.