Q

# How would you account for the following: Cobalt (II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.

8.21 How would you account for the following:

(ii) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidised.

Cobalt (II) is more stable in aq. solution but in presence of strong field ligand complexing agents, it gets oxidised to  Cobalt (III). Though the third ionisation energy of $Co$ is high but the CFSE (crystal field stabilisation energy) is very high in presence of strong field ligand which overcomes the ionisation energy.