Question

The stepwise formation constants for complexes of NH3 with [Cu(OH2)6]2+ (aq) are logK11 = 4.15, log K12= 3.50, log K13 = 2.89, log K14 = 2.13, log K15 = -0.52. Suggest a reason why Kt5 is so different? (10)

Answer 1

K₅ is smaller because the reaction is slower due to steric and electronic effects.

Step-by-step explanation:

K is the rate constant of the reaction. The higher the value of log K, the higher the value of K and the faster is the reaction.

The reaction can be represented by the following reaction:

6 NH₃ + [Cu(OH₂)₆]²⁺ → [Cu(NH₃)₆]²⁺ + 6 H₂O

This means that the reaction is exchanging the H₂O ligands by NH₃ ligands.

The more NH₃ ligands we add to the complex, the more difficult (slower) is the substitution. This happend because the addition of NH₃ ligands promotes a steric hindrance and electronic repulsion, which makes it harder for the next NH₃ to approach the complex and substitute the H₂O ligand.

This is the reason why K₅ is negative. The rate of this substitution is extremelhy low.