Question

At the atomic level, what is the difference between Cobalt II chloride and Cobalt III chloride? Perform a literature search and discuss the difference between the properties of Cobalt II and Cobalt III.

Answer 1

SOLUTION:

(1) CoCl2 is a very stable compound where as CoCl3is not.

(2) If we analyse the reduction potential of Co(III) (+1.92 V) and Chlorine (+1.36 V)

Hence, Co(III) easily reduced to Co(II) as its reduction potential is higher than chlorine and ultimately CoCl2 will be there.

However, CoF3 is stable as reduction potential of fluorine to fluoride +2.87 V which is higher than Co(III) reduction potential.

(3) In the presence of NH3 or amines, Co(II) is readily oxidised by atmospheric oxygen to give a variety of Co(III) complexes. For example, the presence of NH3triggers the oxidation of Co(II) chloride to hexamminecobalt(III) chloride:

e.g.   4 CoCl2•6H2O + 4 NH4Cl + 20 NH3 + O2 → 4 [Co(NH3)6]Cl3 + 26 H2O

(4) Unlike Co(II) complexes, Co(III) complexes are very slow to exchange ligands, so they are said to be kinetically inert