Brown Ring Test

The brown ring test is a chemical procedure for determining the presence of nitrate ions in a sample. The nitrate test is another name for it. It’s a standard qualitative test for confirming the presence of nitrate ions in any solution that results in the creation of a brown-coloured ring. The addition of ferrous sulphate to the supplied solution, which contains nitrate ions, results in the formation of a brown ring, which is further acidified by adding strong sulphuric acid to the entire mixture. At the intersection of sulphuric acid and ferrous sulphate, a brown ring is usually created. The presence of nitrates in the solution is indicated by this ring.           

How to do the Brown Ring Test?

The reaction of ferrous sulphate with strong sulphuric acid is used in the brown ring test. In general, the reaction that occurs in the experiment is a reduction reaction. If there is nitrate in the sample, it combines with ferrous sulphate solution and forms nitric oxide. Ferrous (II) is converted to ferrous (III) (III). The nitrosyl complex is formed when nitric oxide, which was formed as a byproduct of the reduction, reacts with the remaining ferrous (II). NO – is formed when nitric oxide is reduced. A brown ring forms at the intersection of the two layers as a result of this. The existence of nitrate ion in the supplied solution is confirmed by the formation of a brown ring.

Steps to follow during the Brown Ring Test

1. Place the given sample, which may contain nitrate ions, in a test tube.

2. In a separate test tube, make a fresh ferrous sulphate solution.

3. When the ferrous sulphate solution is ready, combine it with the sample in the test tube.

4. Add concentrated sulphuric acid along the test tube’s wall in the same test tube.

5. When adding concentrated sulphuric acid, tilt the test tube slightly. This allows the acid to sink to the bottom of the test tube, resulting in the creation of a brown ring at the intersection of the two layers.

6. Don’t jiggle the test tube once the brown ring has formed, since this may cause the brown ring to dissolve into the solution.

At the intersection of the two layers generated by the mixture of the provided compound, ferrous sulphate solution, and sulphuric acid, a brown ring forms. The presence of nitrate ions in the supplied sample of the chemical is confirmed by the brown ring.

Brown Ring Test with the Equation

The nitrate ion is reduced to nitric oxide by iron(II), which is then oxidised to iron(III), followed by the formation of a nitrosyl complex between the nitric oxide and the remaining iron(II), where nitric oxide is reduced to NO -.

First equation: Chemists assumed that nascent oxygen is formed at this point, and that the oxidation is carried out by [O]. Finally, FeSO4 occurs as [Fe (H2O)6] in aqueous solution. SO4 is a molecule that interacts with NO.

Second equation:This stage produces a brown-colored compound called Iron (III) Penta aqua nitrosyl sulphate.

[Fe(H2O)5(NO)]:The brown ring complex (SO4)

Nitric Acid in Brown Test

• Ammonium nitrate for fertilisers and other nitrates for explosives and pyrotechnics are the most prevalent uses for nitric acid

• It can also be used to make nitro-glycerine, trinitrotoluene, and other organic nitro compounds

• Other notable applications include pickling stainless steel, etching metals, and use as an oxidant in rocket fuels

Uses of Brown Ring Test

1. When you fertilise plants, you’re adding nitrates to the soil. But what happens to nitrates? Many are used by plants for growth, while others are absorbed by the soil. When there are large levels of nitrates in the soil, there may be significant amounts of nitrates in the groundwater. Because excessive levels of nitrates can be dangerous to humans, well water should be tested to see if the nitrates are above the allowable limit.
2. Nitrates in the water cannot be tasted, smelled, or seen. You will notice excessive sulphur levels in your water long before they become dangerous because they will taste and smell terrible. We are ignorant that we are drinking poisoned water since nitrates have no taste or odour.

Conclusion

A nitrate test is a chemical procedure for determining the presence of the nitrate ion in a solution. Wet chemistry testing for the presence of nitrate is more difficult than testing for other anions since practically all nitrates are soluble in water. Many common ions, on the other hand, precipitate insoluble salts, such as halides with silver and sulphate with barium.Because the nitrate anion is an oxidant, many nitrate anion assays are based on this feature. Other oxidants in the analyte, on the other hand, may interact and cause false readings.Nitrate can also be identified by converting it to the more reactive nitrite ion and then testing it with one of the various nitrite assays available.