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please explain the brown ring process

The reaction of Nitrate radical with ferrous sulphate on slowly adding concentrated sulphuric acid results in the appearance of a brown ring (due to the formation of a nitrosyl complex) at the junction of the two liquids which acts as an indicator for the presence of nitrate  radical.

 Nitrate ion is hydrophilic. Almost all nitrates are water-soluble, thus it is difficult to obtain a precipitate to detect its presence. Thus the property of Nitrate that can be used to detect its presence is its oxidizing property. Ferrous ion is oxidized to Ferric to form a highly unstable nitrosyl complex (brown ring) which decomposes even on gentle warming.


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