Question

a.) Assuming the displacement of a water by a ligand were so favored that the back reaction could be ignored, calculate all the stepwise formation constants you would expect in the formation of [Ni(NH₃)₃(OH₂)₃]²⁺ from [Ni(NH₃)₂(OH₂)₄]²⁺.

b.) The standard potentials for the couples Pb²⁺/Pb and Pb⁴⁺/ Pb²⁺ are +1.8 V and -0.126 V, respectively. Should we expect Pb²⁺ to disproportionate in aqueous solution?

Answer 1

a) Your question in incorrect as, Ni has coordination of six, it must have oxidation number of +4, but in the present question it is given +2

b) The question is not about disproportionate, but comproportionate, in which the two reactants having same element in different oxidation number react to  form product in which the oxidation number is same, this is just the opposite of disproportionation, and it happens in case of lead acid battery.

Pb + PbO₂ + H₂SO₄ => PbSO₄ + 2H₂O

The reverse reaction is non-spontansous, but is possible only by during recharging