Nitrate
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{{dablink|'''Trinitrate''' redirects here. See also [[glyceryl trinitrate]]. For the film stock see [[nitrocellulose]].}}
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[[Image:Nitrate-ion-elpot.png|thumb|right|200px|An [[electric potential|electrostatic potential]] map of the nitrate ion. Areas coloured red are lower in energy than areas coloured yellow. The oxygen atoms carry the majority of the negative charge.]]
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[[Image:Nitrate-ion-2D.png|thumb|right|200px|The structure and bonding of the nitrate ion. The N−O bonds are intermediate in length and strength between a single bond and a double bond.]]
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In [[inorganic chemistry]], a '''nitrate''' is a [[salt (chemistry)|salt]] of [[nitric acid]] with an [[ion]] composed of one [[nitrogen]] and three [[oxygen]] atoms (NO<sub>3</sub><sup>−</sup>). In [[organic chemistry]] the [[esters]] of nitric acid and various [[alcohols]] are called nitrates.
==Chemical properties==
The '''nitrate ion''' is a [[polyatomic ion|polyatomic]] [[ion]] with the [[empirical formula]] [[nitrogen|N]][[oxygen|O]]<sub>3</sub><sup>−</sup> and a [[molecular mass]] of 62.0049. It is the [[conjugate acid|conjugate base]] of nitric acid, consisting of one central nitrogen [[atom]] surrounded by three identical oxygen atoms in a [[trigonal planar]] arrangement. The nitrate ion carries a [[formal charge]] of negative one, where each oxygen carries a −2/3 charge while the nitrogen carries a +1 charge, and is commonly used as an example of [[Resonance (chemistry)|resonance]]. The three canonical structures of the nitrate ion are shown resonating below:
<div style="text-align: center">[[Image:Nitrate-ion-resonance-2D.png|400px|Canonical forms of the nitrate ion resonating]]</div>
Almost all inorganic nitrate salts are [[solubility|soluble]] in [[water]] at [[standard temperature and pressure]].
In [[organic chemistry]] a nitrate is a [[functional group]] with general chemical formula RONO<sub>2</sub> where R stands for any organic residue. They are the [[esters]] of nitric acid and [[alcohols]] formed by '''nitroxylation'''. Examples are '''methyl nitrate ''' formed by reaction of [[methanol]] and nitric acid,<ref>{{OrgSynth | author = Black, A. P.; Babers, F. H. | year = 1939 | prep = cv2p0412 | title = Methyl nitrate | collvol = 2 | collvolpages = 412}}</ref> the nitrate of [[tartaric acid]],<ref>{{OrgSynth | author = Snyder, H. R.; Handrick, R. G.; Brooks, L. A. | year = 1942 | title = Imidazole | prep = cv3p0471 | collvol = 3 | collvolpages = 471}}</ref> and the inappropriately named [[nitroglycerin]].
==Related materials==
Nitrates should not be confused with [[nitrite]]s (NO<sub>2</sub><sup>−</sup>) the salts of [[nitrous acid]]. [[Organic compound]]s containing the nitro [[functional group]] (which has the same formula and structure as the nitrate ion save that one of the O<sup>−</sup> atoms is replaced by the R group) are known as [[nitro compound]]s.
==Human toxicity==
High levels of nitrates, most often through [[occupational exposure]] in adults, are toxic to humans. Nitrates [[oxidize]] the [[iron]] atoms in [[hemoglobin]] from [[Ferrous]] [[Iron]] (2+) to [[Ferric]] Iron (3+), rendering it unable to carry [[oxygen]]. This condition is called [[methemoglobinemia]] and can lead to a [[hypoxia|lack of oxygen]] in tissues. Methemoglobinemia is treated with [[methylene blue]].
[[Infants]], in particular, are especially sensitive to methemoglobinemia as a result of nitrate exposure. This is most caused by high levels of nitrates in drinking water.
==Marine toxicity==
In [[freshwater]] or [[estuary|estuarine]] systems close to land, nitrate can reach high levels that can potentially cause the death of fish. While nitrate is much less toxic than ammonia or nitrite,<ref>Romano, N.; Zeng, C. (2007). "Acute toxicity of sodium nitrate, potassium nitrate and potassium chloride and their effects on the hemolymph composition and gill structure of early juvenile blue swimmer crabs (''Portunus pelagicus'', Linneaus 1758) (Decapoda, Brachyura, Portunidae)." ''Environmental Toxicology and Chemistry'' '''26''': 1955–1962.</ref> levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species.{{Fact|date=February 2007}} However, in light of inherent problems with past protocols on acute nitrate toxicity experiments, the extent of nitrate toxicity has been the subject of recent debate.<ref>{{cite journal | author = Romano N., Zeng, C. | year = 2007 | title = Effects of potassium on nitrate mediated changes to osmoregulation in marine crabs | journal = [[Aquatic Toxicology]] | volume = 85 | pages = 202–208 | doi = }}</ref>
In most cases of excess nitrate concentrations in aquatic systems, the primary source is [[surface runoff]] from agricultural or [[landscape]]d areas which have received excess nitrate fertilizer. These levels of nitrate can also lead to algae blooms, and when nutrients become limiting (such as potassium, phosphate or nitrate) then [[eutrophication]] can occur. As well as leading to water [[Hypoxia (environmental)|anoxia]], these blooms may cause other changes to [[ecosystem]] function, favouring some groups of organisms over others. Consequently, as nitrates form a component of [[total dissolved solids]], they are widely used as an indicator of [[water quality]].
Nitrates are also a by-product of [[septic tank|septic systems]]. Specifically, they are a naturally occurring chemical that is left after the break down or decomposition of animal or human waste. Water quality may also be affected through ground water resources that have a high number of septic systems in a watershed. Septics leach down into ground water resources or aquifers and supply near by bodies of water. Lakes that rely on ground water are often affected by nitrification through this process.
==See also==
* [[Ammonium]]
* [[f-ratio]]
* [[Nitrification]]
* Nitrate overview:
{{nitrates}}
{{commonscat|nitrates}}
== External links ==
* [http://www.atsdr.cdc.gov/csem/nitrate/ ATSDR - Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity]
==References==
<div class="references-small"><references/><div>
[[Category:Oxoanions]]
[[Category:Nitrates| ]]
[[Category:Nitrogen metabolism]]
[[Category:Curing agents]]
[[Category:Garde manger]]
[[Category:Water quality indicators]]
[[Category:functional groups]]
[[Category:Non-coordinating anions]]
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