Nitrate

Nitrate, named by IUPAC, is a polyatomic ion containing nitrogen and oxygen in it. When a proton is removed from nitric acid, a nitrate ion is formed. The molecular formula of nitrate is NO⁻ ₃. Nitrate ions form salts called nitrates. The conjugate base of nitrate is nitric acid. The structure of nitrate is a nitrogen atom at the center bonded with three identical oxygen atoms. The arrangement of the atoms is in trigonal planar. The formal charge of nitrate ion is -1 because the nitrogen atom carries a charge +1 and each of the three oxygen atoms carries a charge -2/3. These combine with the formal charge of the nitrate ion. Similar to the isoelectronic carbonate ion, the nitrate ion shows resonance. The resonant structures of nitrate ion are shown below

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Chemical Properties of Nitrate

• The molecular weight (molar mass) is 62.005 g/mol

• The XLogP3-AA is -1.4

• The number of hydrogen bond donor is 0

• The number of hydrogen bond acceptor is 3

• The number of rotatable bonds is 0

• The topological polar surface area is 62.9 Ų

• The number of heavy atoms is 4

• It has a single covalent bond

• Nitrate ion has no isotope atom

• It has no defined atom stereocenter

• It has no undefined atom stereocenter

• It has no defined bond stereocenter

• It has no undefined bond stereocenter

Conversion of Nitrogen to Nitrate

The conversion of nitrogen to nitrate can be observed in the nitrogen cycle. Single-celled prokaryotes and bacteria trap the atmospheric nitrogen, N2, and converts it through nitrogen fixation into a biologically usable form. These nitrogen-fixing bacteria either live freely in soil and water or, live inside plants as beneficial symbionts. These microorganisms convert the trapped nitrogen and convert them into ammonia, NH3. Plants use this ammonia to make organic molecules. When these plants get eaten up, the nitrogen is transferred to the animals. It is then either excreted by the animal as waste or, incorporated into the body. This nitrogen does not remain in the animal’s body forever. In the end, the organic nitrogen gets converted back into atmospheric nitrogen gas with the help of bacteria. The wastes from animals and decays containing nitrogenous compounds are converted into ammonia by bacteria, which is further converted into nitrite and nitrate. The denitrifying prokaryotes convert the nitrates into atmospheric nitrogen gas, N2. 

Conversion of Nitrite to Nitrate 

The conversion of nitrite to nitrate is observed in a process named Nitrification. It is an aerobic process. When ammonia oxidizes to nitrite biologically and then the nitrite converts to nitrate by oxidation, the process is known as nitrification. One of the most important stages in the nitrogen cycle is nitrification. Nitrification is carried out by archaea and autotrophic bacteria. After the ammonia oxidation, the next step is nitrite oxidation where the bacteria oxidize nitrite into nitrate. Such bacteria are Proteobacteria, Nitrospinae, Chloroflexi and Nitrospirae. These bacteria are found in geothermal springs, soli, marine ecosystems, and freshwater. 

Occurrence and Availability

Nitrates are majorly found on earth as huge deposits of salts, particularly nitratine, which is a source of sodium nitrate. Nitrifying bacteria and other species produce nitrates in the natural environment by using urea and ammonia as a source of nitrogen. By various fermentation processes, urine and dung were also used to produce nitrate and used as gunpowder in historical times. In the atmosphere rich in oxygen and nitrogen when hit with lightning strikes, a mixture of oxides of nitrogen are formed which produces nitrate ions. These nitrate ions are then rained down from the atmosphere. Industrially, nitrate ions are prepared by nitric acid.

Conclusion

Nitrates are found in groundwater and surface levels which generally do not affect our health but if the levels of nitrate are high, it has adverse effects on us. Due to improper well construction, overuse of fertilizers, improper well location, or improper disposal of animal or human waste nitrate levels gets high in well waters. Heating or boiling of the nitrate-rich water will not remove nitrate as due to evaporation of water, water levels in the solution may decrease which in turn makes the solution more concentrated in nitrate. Through chlorination (chemical disinfection) or mechanical filters, nitrate can not be removed from the water. Nitrate treatment processes like reverse osmosis, ion exchange, and distillation can successfully remove nitrate from water.

Do You Know?

1. Few of the identifiers of nitrate are PubChem CID 943, ChemSpider 918, and CAS number 14797-55-8.

2. Nitrates are canonicalized compounds.