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Explain the brown ring test for nitrate ions. |
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Answer» Solution :The brown ring test for nitrates depends on the ABILITY of `FE^(2+)` to reduce nitrates to nitric oxide (NO) that reacts with `Fe^(2+)` to form a brown ring complex. To a sample CONTAINING `NO_(3)^(-)`ions, a dilute ferrous sulphate solution is added and then concentrated sulphuric acid is added carefully ALONG the SIDES of test tube. A brown ring at the interface between the solution and sulphuric acid layers indicates the presence of nitrate ions in the solution. `NO_(3)^(-) + 3Fe^(2+) + 4H^(+) to NO + Fe^(3+) + 2H_(2)O` `[Fe(H_(2)O)_(6)]^(2+) + NO to underset("Brown complex")([Fe(H_(2)O)_(5).(NO)]^(2+) + H_(2)O)` |
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