Chemistry of transition elements: describe question

The stability constant, $K_{\text{stab}}$, is an equilibrium constant for the formation of a complex ion. Two cobalt(III) complexes are:

• $\ce{[Co(NH3)6]^{3+}}$ has $K_{\text{stab}} = 4.5 \times 10^{33}$
• $\ce{[Co(H2O)6]^{3+}}$ has $K_{\text{stab}} = 1.0 \times 10^{18}$

(a) Define the term stability constant, $K_{\text{stab}}$, for the formation of a complex ion in aqueous solution.

(b) Write the expression for $K_{\text{stab}}$ for the formation of $\ce{[Co(NH3)6]^{3+}}$ from its constituent ions in aqueous solution.

(c) Explain why the $K_{\text{stab}}$ value for $\ce{[Co(NH3)6]^{3+}}$ is larger than that for $\ce{[Co(H2O)6]^{3+}}$.

(d) When concentrated aqueous ammonia is added to a solution containing $\ce{[Co(H2O)6]^{3+}}$, ligand exchange occurs to form $\ce{[Co(NH3)6]^{3+}}$. Describe and explain this process in terms of stability constants.