Brown Ring Test - Nitrate ion, Determination Brown Ring Test, Uses, FAQs

Introduction

Brown ring test is also known as nitrate test or the just the ring test in chemistry, which is used to find out the existence of nitrate ions in a solution or in an organic or inorganic compound during salt analysis. The nitrate test, as the name given is used to determine the nitrate ions, or to test for nitrate ions in a compound’s aqueous solution by the development of brown colored ring complex at the intersection of the layers which is clearly visible by the naked eye. This test is mostly useful in the milligram quantities.

Nitrate ion

Nitrate is an oxo anion that is a negatively charged ion of nitrogen element created by the loss of a nitric acid proton. It is a participant of nitrogen species which are reactive and is also an anion which is monovalent and inorganic in nature. It is a nitric acid conjugate base. The aqueous solution of nitrate ion immediately catches fire when brought in contact with organic compounds. It is usually non-combustible in nature but will hasten the burning of materials which easily gets on combustion.

The structure of nitrate ion has trigonal planar geometry comprising of one nitrogen atom at the center which is occupied by three same oxygen atoms bonded to the central atom. The nitrate ion has a charge of -1. It is usually denoted as NO^-₃. The nitrate ion can also be regarded with resonance structures.

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Sources of nitrate

Leafy vegetables comprise of a major constituent of nitrate in inorganic form. It is also found in vegies and beetroot juice in a good amount. Drinking water from the RO is also a good source of inorganic nitrate in daily life.

Inorganic nitrate salts are found in earth’s crust in big deposit and is also produced from picric acid in industries. Nitrates are also produced from nitrogen fixing bacteria present in the soil, they help maintain the soils and plant’s nitrogen levels.

Uses

Nitrate is a key component of fertilizers used in agriculture for their great abilities like easily degradable in the environment and immense solubility in the aqueous medium. The most common types of fertilizers with nitrate content are calcium, potassium, ammonium, sodium and magnesium salts. A huge concentration of nitrates are usually produces for this purpose. The secondary applications of nitrates are in the manufacture of explosives, because of its oxidizing ability it used in making explosives for the oxidation of carbon compounds.

Also, students can refer,

• NCERT solutions for Class 11 Chemistry Chapter 12 Organic chemistry- some basic principles and
  techniques
• NCERT Exemplar Class 11 Chemistry Solutions Chapter 12 Organic chemistry- some basic principles and
  techniques
• NCERT notes Class 11 Chemistry Chapter 12 Organic chemistry- some basic principles and techniques

Determination of nitrates

All the determination methods of nitrates rely on the fact of its conversion to nitrite, which is determined by nitrite detection tests. The conversion from nitrate to nitrite is affected by cadmium and copper material. Another method used for detection, called the Griess test in which nitrite is transformed into a dye known as azo dye which is a deeply colored complex, which is convenient for UV spectroscopy analysis. In this test the activity of nitrous acid is destroyed procured by nitrite acidification. The aromatic amines which are particularly reacted by nitrous acid to get diazonium salt, which instead react with next reagent to give azo dye. Another method of detection of nitrate ions is the ring test in chemistry, more precisely it is known as brown ring test.

Brown ring test:

Experiment title: to determine the presence of nitrate ions in the given test sample.

Apparatus: freshly made solution of iron sulphate, given glass test tubes, concentrated sulfuric acid.

The principle behind the detection of nitrate ion by brown ring test: the principle of the test is dependent on the fact that the nitrate ion is oxidizing in nature. The reduction of nitrate ion by iron (||) and iron (||) gets oxidized to iron (|||) in the reacting solution. The reduction of NO from nitrous oxide forms nitroso complex which can be clearly visible by the appearance of a brown colored ring at the intersection of the two layers, which is formed by this nitroso complex. The first layer out of the two layers is the solution of iron sulphate and the second layer is the solution of concentrated sulfuric acid. The appearance of the brown ring, validate the presence of nitrate ions in the given sample solution.

Method of the brown ring test procedure given step wise:

1. Take the given sample solution in which you have to determine the presence of nitrate ions in a glass test tube.
2. Make a fresh solution of iron sulphate.
3. Now combine the freshly made solution of iron sulphate with the given sample in which we have to confirm the presence of nitrate ions.
4. Now from the sides of the glass test tube containing the iron sulphate solution and test sample, add concentrated sulfuric acid to the bottom of the test tube and tilt it slightly. The addition of sulfuric acid should be in a way such that it creates a layer below the water solution.

Inspection of the practical

A brown colored ring complex is visible at the intersection of the two aqueous layers, out of which one layer is of solution of iron sulphate and other one is of concentrated sulfuric acid layer.

Brown ring test reaction

The brown test reaction is as follows

The nitrate ion reduction, iron (||) oxidation and nitrous oxide reduction Is given in the equation below.

3H₂SO₄ + 2HNO₃ + 6FeSO₄→ 3Fe₂(SO₄)₃ + 2NO + 4H₂O

[Fe (H2O)₆]SO₄ + NO → [Fe (H₂O)₅(NO)]SO₄+ H₂O

Nitroso complex water

The test is quite valid in milligrams quantity.

Uses of brown ring test

The main application of brown ring test is to detect the presence of nitrate ions in the given test solution. In food industries too it has applications in detecting nitrates in food samples to ensure quality check, as high levels of nitrates in the food can cause carcinogenesis and a disease of red blood cells called the methemoglobinemia. Higher levels of nitrates in the soil make it acidic in nature which is hazardous for the plants growing in the soil and the animals grazing on the land plants, so here the brown ring test plays an important role in the detection of nitrates in the soil samples. If the drinking water has nitrate compounds more than 10 mg per liter then it's not suitable for human or animal consumption.

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NCERT Chemistry Notes:

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