What is brown ring test

what is brown ring test

A nitrate test is a chemical test used to determine the presence of nitrate ion in solution.

A nitrate test, known as the brown ring test can be performed by adding iron(II) sulfate to the solution, then slowly adding concentrated sulfuric acid and watching for a brown ring on the test tube, which will indicate the presence of the nitrate ion.

The test follows several phases; these have been written as balanced chemical equations:
1: 2 Zn(NO3)2 + 2 H2SO4 ? 2 ZnSO4 + 4 HNO3

4 FeSO4 + 2 H2SO4? 2 Fe2(SO4 )3 + H2
These two reactions happen simultaneously.

2: 4 HNO3 ? 2 H2O + 3O2 + 2 NO
The Nitric Acid decomposes in the intense heat produced by the high concentrate Sulphuric Acid used.

3: 2 Fe2(SO4)3 + 2 H2 + 4 NO ? 4 Fe.NO.SO4 + 2 H2SO4

The Fe.NO.SO4 forms a brown ring in the middle of the solution produced by the reaction, making it easy to identify the presence of nitrates in the water.