The brown ring test for nitrates depends on

Options

A. the reduction of nitrate to nitric oxide
B. oxidation of nitric oxide to nitrogen dioxide
C. reduction of ferrous sulphate to iron
D. oxidising action of sulphuric acid

Answer

A

Explanation

The brown ring is appeared due to the formation of a brown complex between nitric oxide (formed as a result of reduction of the nitrate ion by the `Fe^(2+)` ions) and `Fe^(2+)` ions.
`NO_(3(aq))^(-)+3Fe_((aq))^(2+)+4H_((aq))^(+)to NO_((g))+3F_((aq))^(3+)+2H_(2)O_((l))`
`underset("pentaaquanitrosonium iron (I) (Brown complex)")(Fe_((aq))^(2+)+NO_((g))+5H_(2)O_((l))to [Fe(H_(2)O)_(5)NO^(+)]^(2_((aq))^(+))`