Question

Why is our system (trans-[Co(N-N)₂Cl₂]⁺ + H₂O ----> trans-[Co(N-N)₂Cl(H₂O)]²⁺ + Cl- ) a better choice for studying the exchange of chloro and aqua ligands (ie: cl- and H2O) than the apparently simpler process shown below

[CoCl6]3– + 6 H2O ⟶ [Co(H2O)6]3+ + 6 Cl–

Answer 1

Because in the first reaction, only one aqua and one chloro ligands (each) are being exchanged. Thus, they can be chemically tagged and their exchange can be monitored and studied.

On the other hand, the second reaction involves 6 ligands of aqua and chloro each. Labeling of the ligands can be confusing in this case and identifying which ligand has proceeded to react in what order can be ambiguous. Hence the choice of first reaction to study the exchange of the two type of ligands is a better one.