Please explain this text i cant understand this text, i mean what is brown ring test....
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.
12 FeSO4 + 3O2 4 Fe2 (SO4)3 + 2Fe2O3 Thus the brown ring which is a brown complex. [ Fe(H2O)5 NO] SO4 will not be obtained.
Ring test is a test to determine the presence of a particular group in a given salt. The most famous test is the brown ring test for the confirmation of presence of nitrate in a salt.
This test is carried out when ferrous sulphate solution is added to a solution of nitrate salt, and conc. sulphuric acid is added slowly to the solution so that it forms a layer below the aqueous solution. The confirmation for nitrate is the formation of a brown ring at the juncture of the two layers.
NO3- + 3Fe2+ + 4H+ → 3Fe3+ + NO + 2H2O
[Fe(H2O)6]2+ + NO → [Fe(H2O)5(NO)]2+ + H2O