Question

Why it is advisable to freshly prepare Ferrous sulphate solution for experiments?

Answer 1

Freshly prepared ferrous sulphate is used in brown ring test, because if FeSO4 is stored or it is the old one then it reacts with atmospheric oxygen and gets oxidized to form a corrosive brown-yellow coating of basic ferric sulphate, which is an adduct of ferric oxide and ferric sulphate.

12FeSO4 + 3O2 → 4 Fe2(SO4)3 + 2Fe2O3

Thus the brown ring which is a brown complex,[Fe(H2O)5NO]SO4will not be obtained.