A Nitrate Test is a

chemical test In chemistry, a chemical test is a qualitative or quantitative procedure designed to identify, quantify, or characterise a chemical compound or chemical group. Purposes Chemical testing might have a variety of purposes, such as to: * Determine ...

used to determine the presence of

nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...

ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in water. In contrast, many common ions give insoluble salts, e.g. halides precipitate with silver, and sulfate precipitate with barium. The nitrate anion is an oxidizer, and many tests for the nitrate anion are based on this property. However, other oxidants present in the analyte may interfere and give erroneous results. Nitrate can also be detected by first reducing it to the more reactive

nitrite The nitrite ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite also ...

ion and using one of many nitrite tests.

Brown ring test

A common nitrate test, known as the brown ring testEgon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier can be performed by adding

iron(II) sulfate Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the heptahydrate (''x'' = 7) but several values for x are know ...

to a solution of a nitrate, then slowly adding concentrated

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

such that the acid forms a layer below the aqueous solution. A brown ring will form at the junction of the two layers, indicating the presence of the nitrate ion. Note that the presence of nitrite ions will interfere with this test. The overall reaction is the reduction of the nitrate ion to

nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ...

by iron(II), which is 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⁻. :2HNO₃ + 3H₂SO₄ + 6FeSO₄ → 3Fe₂(SO₄)₃ + 2NO + 4H₂O : e(H₂O)₆O₄ + NO → e(H₂O)₅(NO)O₄ + H₂O This test is sensitive up to 2.5 micrograms and a concentration of 1 in 25,000 parts.

Devarda's test

Devarda's alloy (Copper/Aluminium/Zinc) is a

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth met ...

. When reacted with nitrate in

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and al ...

solution,

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

is liberated. The ammonia formed may be detected by its characteristic odor, and by damp red litmus paper's turning blue, signalling that it is an alkali — very few gases other than ammonia evolved from wet chemistry are alkaline. :3 + 8 Al + 5 + 18 → 3 + 8 Aluminium is the reducing agent in this reaction that will occur.

Diphenylamine test

Diphenylamine Diphenylamine is an organic compound with the formula (C6H5)2NH. The compound is a derivative of aniline, consisting of an amine bound to two phenyl groups. The compound is a colorless solid, but commercial samples are often yellow due to oxidiz ...

may be used as a wet

for the presence of the

ion. In this test, a solution of diphenylamine and ammonium chloride in

is used. In the presence of nitrates, diphenylamine is oxidized, giving a blue coloration. This reaction has been used to test for organic nitrates as well, and has found use in gunshot residue kits detecting

nitroglycerine Nitroglycerin (NG), (alternative spelling of nitroglycerine) also known as trinitroglycerin (TNG), nitro, glyceryl trinitrate (GTN), or 1,2,3-trinitroxypropane, is a dense, colorless, oily, explosive liquid most commonly produced by nitrating ...

and

nitrocellulose Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...

Copper turnings test

The nitrate ion can easily be identified by heating copper turnings along with concentrated sulfuric acid. Effervescence of a brown, pungent gas is observed which turns moist blue litmus paper red. Here sulfuric acid reacts with the nitrate ion to form nitric acid. Nitric acid then reacts with the copper turnings to form nitric oxide. Nitric oxide is thus oxidised to nitrogen dioxide. : + 4 → + 2 +2

References

{{Analytical reagents Chemical tests

Brown ring test

Devarda's test

Diphenylamine test

Copper turnings test

See also

References