Question

write ring reaction

Answer 1

The identification test of nitrate ( NO3–) using conc. H2SO4 and freshly prepared FeSO4 , is known as 'Brown Ring Test'( it is the confirmation test of NO3– too ). In a normal test tube take the supplied NO3– containing sample ( say KNO3 ) . Now add conc.H2SO4 dropwise with gentle shaking and then heat it shortly using Bunsen burner & add freshly prepared greenish FeSO4. Then, you can certainly see a brown ring is formed in that test tube bcz of formation of brown colred [Fe(H2O)5 (NO)]SO4 complex. The rxn equations are belows : I just avoid balance here but it's forbidden… balance is must required in all cases…

KNO3 + H2S04 = KHSO4 + HNO3

HNO3 + FeSO4 = NO + Fe2(SO4)3 + H2O. In this step chemists assumed that nassent oxygen is produced and the oxidation is done by [O]. Nextly, FeSO4 in aqueous solution of course exist as [Fe(H2O)6]SO4, It reacts with NO.

[Fe(H2O)5]SO4 + NO = [Fe(NO)(H2O)5]SO4. —— a brown coloured complex which name is Iron(|||)penta aqua nitrosyl sulphate.

## In 'brown ring' complex, the oxidation state of iron is +3 i.e. Fe(|||) and nitrosyl exists as NO(–), simply, anti-ferromagnetic coupling occur in the complex in b/w these two ions