Question

Knowing that the value of K for [Cu(NH₃)₄]²⁺ is 4.5 × 10¹¹ and for [Cu(CN)₄]²⁻ is 2.0 × 10²⁷, suggest which out of NH₃ and CN⁻ is a stronger ligand.

Answer 1

The stability constant (K) measures the stability of the complex. A higher value of K indicates a stronger ligand because it suggests that the complex is more stable and less likely to dissociate into the metal ion and the ligands.

For [Cu(NH₃)₄]²⁺, the stability constant K = 4.5×10¹¹

For [Cu(CN)₄]²⁻, the stability constant K = 2.0 × 10²⁷

Since the stability constant for [Cu(CN)₄]²⁻ is significantly higher than that for [Cu(NH₃)₄]²⁺, CN⁻ is a stronger ligand than NH₃.