Editing Sodium triphosphate (section)

==Preparation and properties==
Sodium tripolyphosphate is produced by heating a stoichiometric mixture of [[disodium phosphate]], Na<sub>2</sub>HPO<sub>4</sub>, and [[monosodium phosphate]], NaH<sub>2</sub>PO<sub>4</sub>, under carefully controlled conditions.<ref name=GE>{{Greenwood&Earnshaw}}</ref>
:2 Na<sub>2</sub>HPO<sub>4</sub>  +  NaH<sub>2</sub>PO<sub>4</sub>   →   Na<sub>5</sub>P<sub>3</sub>O<sub>10</sub>  +  2 H<sub>2</sub>O
In this way, approximately 2 million tons are produced annually.<ref name=Ullmann/>

STPP is a colourless salt, which exists both in [[anhydrous]] form and as the hexahydrate. The anion can be described as the pentanionic chain [O<sub>3</sub>POP(O)<sub>2</sub>OPO<sub>3</sub>]<sup>5−</sup>.<ref>{{cite journal |last1=Corbridge |first1=D. E. C. |title=The crystal structure of sodium triphosphate, Na<sub>5</sub>P<sub>3</sub>O<sub>10</sub>, phase I |journal=Acta Crystallographica |date=1 March 1960 |volume=13 |issue=3 |pages=263–269 |doi=10.1107/S0365110X60000583 |bibcode=1960AcCry..13..263C }}</ref><ref>{{cite journal |last1=Davies |first1=D. R. |last2=Corbridge |first2=D. E. C. |title=The crystal structure of sodium triphosphate, Na<sub>5</sub>P<sub>3</sub>O<sub>10</sub>, phase II |journal=Acta Crystallographica |date=1 May 1958 |volume=11 |issue=5 |pages=315–319 |doi=10.1107/S0365110X58000876 |doi-access=free |bibcode=1958AcCry..11..315D }}</ref> Many related di-, tri-, and polyphosphates are known including the cyclic triphosphate (e.g. [[sodium trimetaphosphate]]). It binds strongly to metal cations as both a [[bidentate]] and [[tridentate]] [[chelating agent]].
[[Image:Triphosphate chelation.svg|thumb|180px|left|Chelation of a metal cation by triphosphate.]]