What Is Nitrate? Structure, Formation, and Real-World Applications
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?
Few of the identifiers of nitrate are PubChem CID 943, ChemSpider 918, and CAS number 14797-55-8.
Nitrates are canonicalized compounds.
FAQs on Nitrate Explained: Key Properties, Occurrence & Uses
1. What is the chemical formula, charge, and valency of the nitrate ion?
The nitrate ion is a polyatomic ion with the chemical formula NO₃⁻. It consists of one central nitrogen atom bonded to three oxygen atoms. The ion carries a net charge of -1, which means its valency is 1. It is the conjugate base of nitric acid (HNO₃).
2. What are the key chemical and physical properties of nitrates?
Nitrates exhibit several distinct properties that are important in chemistry. Key properties include:
Solubility: Almost all nitrate salts are highly soluble in water. This is a defining characteristic used in qualitative analysis.
Oxidising Agent: The nitrate ion is a strong oxidising agent, especially in acidic conditions, due to the nitrogen atom being in its +5 oxidation state.
Molar Mass: The molar mass of the nitrate ion (NO₃⁻) is approximately 62.005 g/mol.
Structure: The ion has a trigonal planar geometry, with the N-O bonds having resonance character.
Stability: While stable in solution, solid nitrates can decompose upon strong heating to produce nitrites, oxides, or free metals, along with oxygen and nitrogen dioxide gas.
3. What are the most common uses of nitrates in agriculture and industry?
Nitrates are vital compounds with a wide range of applications. Their most common uses include:
Fertilisers: Due to their high solubility and nitrogen content, nitrates like ammonium nitrate (NH₄NO₃) and potassium nitrate (KNO₃) are extensively used as fertilisers to promote plant growth.
Explosives: As powerful oxidising agents, nitrates are a key component in many explosives. For example, ammonium nitrate is used in ANFO (Ammonium Nitrate/Fuel Oil), and nitroglycerin is a nitrate ester used in dynamite.
Food Preservation: Sodium nitrate (NaNO₃) and sodium nitrite (NaNO₂) are used as preservatives in cured meats to prevent bacterial growth and maintain colour.
Glass and Ceramics: Nitrates like sodium nitrate are used to remove air bubbles from molten glass and in the formulation of some ceramic glazes.
4. How is the presence of the nitrate ion detected in a laboratory setting?
The classic laboratory test for the nitrate ion is the Brown Ring Test. The procedure involves:
Making an aqueous solution of the salt sample to be tested.
Adding freshly prepared ferrous sulphate (FeSO₄) solution to it.
Carefully adding concentrated sulphuric acid (H₂SO₄) down the side of the test tube to form a separate layer at the bottom.
If a nitrate ion is present, a brown-coloured ring will form at the junction of the two layers. This ring is due to the formation of the complex ion [Fe(H₂O)₅NO]²⁺.
5. What is the fundamental difference between a nitrate (NO₃⁻) and a nitrite (NO₂⁻) ion?
The main difference between nitrate and nitrite lies in the number of oxygen atoms and the oxidation state of the nitrogen atom.
Structure: Nitrate (NO₃⁻) has three oxygen atoms, while nitrite (NO₂⁻) has only two oxygen atoms.
Oxidation State: In nitrate, the nitrogen atom is in its highest oxidation state of +5. In nitrite, the nitrogen atom is in a lower oxidation state of +3.
Role and Stability: Nitrate is generally more stable. In biological and environmental systems, nitrate is often the end product of nitrification, while nitrite is an intermediate. Nitrite is chemically more reactive and is a stronger oxidising agent than nitrate in some contexts.
6. Why can high levels of nitrates in drinking water be particularly harmful to infants?
High nitrate intake is dangerous for infants due to a condition called methemoglobinemia, or "Blue Baby Syndrome." In an infant's less acidic digestive system, bacteria can convert ingested nitrate (NO₃⁻) into the more toxic nitrite (NO₂⁻). This nitrite then enters the bloodstream and oxidises the iron in haemoglobin from the ferrous (Fe²⁺) state to the ferric (Fe³⁺) state, forming methemoglobin. Unlike haemoglobin, methemoglobin cannot bind and transport oxygen. This leads to oxygen deprivation, causing the skin to turn a bluish colour, and can result in serious illness or even be fatal if left untreated.
7. Why are most nitrate salts highly soluble in water?
The high solubility of most nitrate salts in water is explained by thermodynamics. The nitrate ion (NO₃⁻) is relatively large and has only a single negative charge. This charge is spread out over the entire ion due to resonance. Consequently, the electrostatic forces holding the nitrate ions and metal cations together in a crystal lattice (lattice enthalpy) are relatively weak. When a nitrate salt is placed in water, the energy released when water molecules surround the individual ions (hydration enthalpy) is sufficient to overcome the lattice enthalpy. This favourable energy balance causes the salt to dissolve easily.
