Effect of Ligand Exchange on Stability Constant (CIE A Level Chemistry)

• The stability constants (K_stab) of ligands are often given on a log₁₀ scale so that it becomes easier to compare them with each other
• Ligand exchange in a complex occurs to form a more stable complex with a larger K_stab
• The stability constants can be used to explain the substitution of ligands in a copper complex

Ligand substitution in a Co(II) complex

• When excess ammonia is added to the [CoCl₄]^2- complex a blue solution is obtained

The chloride ligands are substituted by the ammonia ligands to form the more stable ammonia complex

• The formation of the ammonia complex could be explained by comparing the stability of the chloride and ammonia ligands

Stability of chloride and ammonia ligands table

• The stability constant of the ammonia ligand is greater than that of the chloride ligands
• The blue ammonia complex is therefore more stable
• As a result, the position of the equilibrium is shifted to the right