Phosphate 23690 223902437 2008-07-06T12:35:10Z 83.78.46.70 /* Cellular function */ A '''phosphate''', in [[inorganic chemistry]], is a [[Salt (chemistry)|salt]] of [[phosphoric acid]]. Inorganic phosphates are [[mining|mined]] to obtain [[phosphorus]] for use in industry. <ref>[http://fipr1.state.fl.us/PhosphatePrimer ''Phosphate Primer'', website of the Florida Institute of Phosphate Research]</ref> <ref>[http://www.foodproductdesign.com/articles/661ingredient2.html "Figuring Out Phosphates," ''Food Product Design'', June 2006, Lynn A. Kuntz]</ref> In [[organic chemistry]], a phosphate, or [[organophosphate]], is an [[ester]] of phosphoric acid. Organic phosphates are important in [[biochemistry]] and [[biogeochemistry]]. == Chemical properties == [[Image:Phosphate.png|thumb|right|The general chemical structure of a phosphate]] [[Image:Phosphate Group.PNG|right|thumb|This is the [[structural formula]] of the phosphoric acid [[functional group]] as found in a weakly [[acidic]] [[aqueous solution]]. In more [[basic (chemistry)|basic]] aqueous solutions, the group donates the two [[hydrogen]] [[atom]]s and [[ion]]izes as a phosphate group with a negative charge of 2. <ref>{{cite book | last = Campbell | first = Neil A. | authorlink = Neil Campbell | coauthors = Reece, Jane B. | title = Biology | edition = Seventh Edition | publisher = Benjamin Cummings | date = 2005 | location = [[San Francisco, California]] | pages = 65 | id = ISBN 0-8053-7171-0 }}</ref>]] The phosphate ion is a [[polyatomic ion]] with the [[empirical formula]] [[phosphorus|P]][[oxygen|O]]<sub>4</sub><sup>3−</sup> and a [[molar mass]] of 94.973 g/mol; it consists of one central [[phosphorus]] atom surrounded by four identical oxygen atoms in a [[tetrahedron|tetrahedral]] arrangement. The phosphate ion carries a negative three formal charge and is the [[conjugate acid|conjugate base]] of the hydrogenphosphate ion, H<sub></sub>PO<sub>4</sub><sup>2−</sup>, which is the conjugate base of H<sub>2</sub>PO<sub>4</sub><sup>−</sup>, the dihydrogen phosphate ion, which in turn is the conjugate base of H<sub>3</sub>PO<sub>4</sub>, [[phosphoric acid]]. It is a [[hypervalent molecule]] (the phosphorus atom has 10 electrons in its [[valence shell]]). Phosphate is also an [[organophosphorus]] compound with the formula OP(OR)<sub>3</sub> A phosphate salt forms when a positively-charged ion attaches to the negatively-charged oxygen atoms of the ion, forming an ionic [[chemical compound|compound]]. Many phosphates are not [[solubility|soluble]] in [[water]] at [[standard temperature and pressure]]. In dilute aqueous solution, phosphate exists in four forms. In strongly-basic conditions, the phosphate ion (PO<sub>4</sub><sup>3−</sup>) predominates, whereas in weakly-basic conditions, the hydrogen phosphate ion (HPO<sub>4</sub><sup>2−</sup>) is prevalent. In weakly-acid conditions, the dihydrogen phosphate ion (H<sub>2</sub>PO<sub>4</sub><sup>−</sup>) is most common. In strongly-acid conditions, aqueous phosphoric acid (H<sub>3</sub>PO<sub>4</sub>) is the main form. <gallery> Image:3-phosphoric-acid-3D-balls.png|<center>H<sub>3</sub>PO<sub>4</sub></center> Image:2-dihydrogenphosphate-3D-balls.png|<center>H<sub>2</sub>PO<sub>4</sub><sup>−</sup></center> Image:1-hydrogenphosphate-3D-balls.png|<center>HPO<sub>4</sub><sup>2−</sup></center> Image:0-phosphate-3D-balls.png|<center>PO<sub>4</sub><sup>3−</sup></center> </gallery> More precisely, considering the following three equilibrium reactions: :H<sub>3</sub>PO<sub>4</sub> {{Unicode|&#8652;}} H<sup>+</sub> + H<sub>2</sub>PO<sub>4</sub><sup>−</sup> :H<sub>2</sub>PO<sub>4</sub><sup>−</sup> {{Unicode|&#8652;}} H<sup>+</sub> + HPO<sub>4</sub><sup>2−</sup> :HPO<sub>4</sub><sup>2−</sup> {{Unicode|&#8652;}} H<sup>+</sub> + PO<sub>4</sub><sup>3−</sup> the corresponding constants at 25°C (in mol/L) are (see [[phosphoric acid]]): : <math> K_{a1}=\frac{[\mbox{H}^+][\mbox{H}_2\mbox{PO}_4^-]}{[\mbox{H}_3\mbox{PO}_4]}\simeq 6.92\times10^{-3}</math> : <math>K_{a2}=\frac{[\mbox{H}^+][\mbox{HPO}_4^{2-}]}{[\mbox{H}_2\mbox{PO}_4^-]}\simeq 6.17\times10^{-8}</math> : <math> K_{a3}=\frac{[\mbox{H}^+][\mbox{PO}_4^{3-}]}{[\mbox{HPO}_4^{2-}]}\simeq 4.79\times10^{-13}</math> For a strongly-basic pH (pH=13), we find : <math>\frac{[\mbox{H}_2\mbox{PO}_4^-]}{[\mbox{H}_3\mbox{PO}_4]}\simeq 7.5\times10^{10} \mbox{ , }\frac{[\mbox{HPO}_4^{2-}]}{[\mbox{H}_2\mbox{PO}_4^-]}\simeq 6.2\times10^5 \mbox{ , } \frac{[\mbox{PO}_4^{3-}]}{[\mbox{HPO}_4^{2-}]}\simeq 2.14</math> showing that only PO<sub>4</sub><sup>3−</sup> and HPO<sub>4</sub><sup>2−</sup> are in significant amounts. For a neutral pH (for example the cytosol pH=7.0), we find : <math> \frac{[\mbox{H}_2\mbox{PO}_4^-]}{[\mbox{H}_3\mbox{PO}_4]}\simeq 7.5\times10^4 \mbox{ , }\frac{[\mbox{HPO}_4^{2-}]}{[\mbox{H}_2\mbox{PO}_4^-]}\simeq 0.62 \mbox{ , } \frac{[\mbox{PO}_4^{3-}]}{[\mbox{HPO}_4^{2-}]}\simeq 2.14\times10^{-6}</math> so that only H<sub>2</sub>PO<sub>4</sub><sup>−</sup> and HPO<sub>4</sub><sup>2−</sup> ions are in significant amounts (62% H<sub>2</sub>PO<sub>4</sub><sup>−</sup>, 38% HPO<sub>4</sub><sup>2−</sup>). Note that in the extracellular fluid (pH=7.4), this proportion is inverted (61% HPO<sub>4</sub><sup>2−</sup>, 39% H<sub>2</sub>PO<sub>4</sub><sup>−</sup>). For a strongly-acid pH (pH=1), we find : <math>\frac{[\mbox{H}_2\mbox{PO}_4^-]}{[\mbox{H}_3\mbox{PO}_4]}\simeq 0.075 \mbox{ , }\frac{[\mbox{HPO}_4^{2-}]}{[\mbox{H}_2\mbox{PO}_4^-]}\simeq 6.2\times10^{-7} \mbox{ , } \frac{[\mbox{PO}_4^{3-}]}{[\mbox{HPO}_4^{2-}]}\simeq 2.14\times10^{-12}</math> showing that H<sub>3</sub>PO<sub>4</sub> is dominant with respect to H<sub>2</sub>PO<sub>4</sub><sup>&minus;</sup>. HPO<sub>4</sub><sup>2&minus;</sup> and PO<sub>4</sub><sup>3&minus;</sup> are practically absent. Phosphate can form many polymeric ions such as [[diphosphate]] (also [[pyrophosphate]]), P<sub>2</sub>O<sub>7</sub><sup>4−</sup>, and [[triphosphate]], P<sub>3</sub>O<sub>10</sub><sup>5−</sup>. The various [[metaphosphate]] ions have an empirical formula of PO<sub>3</sub><sup>−</sup> and are found in many compounds. Phosphate deposits can contain significant amounts of naturally occurring [[uranium]]. Uptake of these substances by plants can lead to high uranium concentrations in crops. == Cellular function == Phosphate is useful in animal [[cell]]s as a [[buffering agent]]. The kinds of phosphate that are useful as buffers include NaH<sub>2</sub>PO<sub>4</sub> and H<sub>2</sub>PO<sub>4</sub><sup>-</sup>. == See also == <div style="-moz-column-count:2; column-count:2;"> *[[organophosphorus]] compounds *[[Phosphine]] - PR<sub>3</sub> *[[Phosphine oxide]] - OPR<sub>3</sub> *[[Phosphinite]] - P(OR)R<sub>2</sub> *[[Phosphonite]] - P(OR)<sub>2</sub>R *[[Phosphite]] - P(OR)<sub>3</sub> *[[Phosphinate]] - OP(OR)R<sub>2</sub> *[[Phosphonate]] - OP(OR)<sub>2</sub>R *Phosphate - OP(OR)<sub>3</sub>, such as [[triphenyl phosphate]] *[[Polyphosphate]] - P<sub>n</sub> </div> == Further reading == {{Expert-subject|Chemicals}} * Schmittner Karl-Erich and Giresse Pierre, 1999. Micro-environmental controls on biomineralization: superficial processes of apatite and calcite precipitation in Quaternary soils, Roussillon, France. Sedimentology 46/3: 463-476. * http://www.fluoridealert.org/phosphate/overview.htm#9, discusses environmental hazards of the phosphate fertilizer industry == References == <!--See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for an explanation of how to generate footnotes using the <ref> and </ref> tags and the tag below --> {{reflist}} == External links == * [http://www.phosphorus-recovery.tu-darmstadt.de Website of the Technische Universität Darmstadt and the CEEP about Phosphorus Recovery] [[Category:Functional groups]] [[Category:Phosphorus compounds]] [[Category:Organophosphorus]] [[Category:Organophosphates]] [[Category:Phosphates]] [[Category:Oxoanions]] [[ar:فوسفات]] [[bs:Fosfat]] [[bg:Фосфат]] [[ca:Fosfat]] [[cs:Fosfát]] [[da:Fosfat]] [[de:Phosphate]] [[et:Fosfaadid]] [[es:Fosfato]] [[eo:Fosfato]] [[fr:Phosphate]] [[id:Fosfat]] [[it:Gruppo fosfato]] [[he:זרחה]] [[ms:Fosfat]] [[nl:Fosfaat]] [[ja:リン酸塩]] [[no:Fosfat]] [[oc:Fosfat]] [[pl:Fosforany]] [[pt:Fosfato]] [[ru:Фосфаты]] [[simple:Phosphate]] [[sk:Fosforečnan]] [[fi:Fosfaatti]] [[sv:Fosfat]] [[th:ฟอสเฟต]] [[tr:Fosfat]] [[uk:Фосфати]] [[zh:磷酸鹽]]