Editing Perchloric acid (section)

==Properties==
Anhydrous perchloric acid is an unstable oily liquid at room temperature. It forms at least five [[water of crystallization|hydrates]], several of which have been characterized [[X-ray crystallography|crystallographically]]. These solids consist of the [[perchlorate]] anion linked via [[hydrogen bond]]s to H<sub>2</sub>O and [[Hydronium|H<sub>3</sub>O<sup>+</sup>]] centers.<ref name="Almlöf">{{cite journal | last1=Almlöf | first1=J. | last2=Lundgren | first2=J. O. | last3=Olovsson | first3=I. | title=Hydrogen bond studies. XLV. The crystal structure of HClO4.2.5H2O | journal=[[Acta Crystallographica Section B]]: Structural Crystallography and Crystal Chemistry | publisher=International Union of Crystallography (IUCr) | volume=27 | issue=5 | date=15 May 1971 | issn=0567-7408 | doi=10.1107/s0567740871003236 | pages=898–904}}</ref> An example is [[hydronium perchlorate]]. Perchloric acid forms an [[azeotrope]] with water, consisting of about 72.5% perchloric acid. This form of the acid is stable indefinitely and is commercially available. Such solutions are [[hygroscopy|hygroscopic]]. Thus, if left open to the air, concentrated perchloric acid dilutes itself by absorbing water from the air.

Dehydration of perchloric acid gives the anhydride [[dichlorine heptoxide]]:<ref name="Holl">{{cite book|title= Inorganic chemistry |first1= Arnold F. |last1= Holleman |first2= Egon |last2= Wiberg |others= Translated by Mary Eagleson, William Brewer |publisher= Academic Press |year= 2001 |isbn= 0-12-352651-5 |page= 464 |location= San Diego}}</ref>
:2 HClO<sub>4</sub> + [[phosphorus pentoxide|P<sub>4</sub>O<sub>10</sub>]] → Cl<sub>2</sub>O<sub>7</sub> + H<sub>2</sub>P<sub>4</sub>O<sub>11</sub>