Selenic acid
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219067062
2008-06-13T12:25:23Z
Kirikou fr
5168652
{{Chembox new
| Name = Selenic acid
| ImageFile = Selenic-acid-2D.png
<!-- | ImageSize = 130px -->
| ImageName = Selenic acid
| ImageFile1 = Selenic-acid-3D-vdW.png
<!-- | ImageSize1 = 130px -->
| ImageName1 = Selenic acid
| IUPACName = Selenic(VI) acid
| OtherNames = Selenic acid
| Section1 = {{Chembox Identifiers
| SMILES = OSe(O)(=O)O
| CASNo = 7783-08-6
| RTECS = VS6575000
}}
| Section2 = {{Chembox Properties
| Formula = H<sub>2</sub>SeO<sub>4</sub>
| MolarMass = 144.9734 g/mol
| Appearance = Colorless deliquescent crystals
| Density = 2.95 g/cm<sup>3</sup>, solid
| Solubility = 130 g/100 mL (30 °C)
| MeltingPt = 58 °C (331 K)
| BoilingPt = 260 °C (533 K) (decomposes)
| pKa = similar to H<sub>2</sub>SO<sub>4</sub>
| RefractIndex = 1.5174 (D-line, 20 °C)
}}
| Section3 = {{Chembox Structure
| MolShape = tetrahedral at Se
| CrystalStruct =
| Dipole =
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = Corrosive, highly toxic
| NFPA-H = 3
| NFPA-R = 2 | Other=OX
| NFPA-F = 0
| RPhrases = 23/25-33-50/53
| SPhrases = 20/21-28-45-60-61
}}
| Section8 = {{Chembox Related
| OtherAnions = [[selenate]]
| OtherCations = [[selenyl ion]], SeO<sub>2</sub><sup>2+</sup>
| OtherCpds = [[Sulfuric acid]]<br /> [[Selenium dioxide]]
}}
}}
'''Selenic acid''' is the [[chemical compound]] with the [[chemical formula|formula]] H<sub>2</sub>[[selenium|Se]]O<sub>4</sub>. This [[oxoacid]] is more descriptively written (HO)<sub>2</sub>SeO<sub>2</sub>, which emphasises that Se is attached to four oxygen atoms. As predicted by [[VSEPR theory]], the selenium center is tetrahedral.
==Preparation and reactions==
Selenic acid is prepared by oxidation of [[selenium dioxide]] with [[hydrogen peroxide]]:
:SeO<sub>2</sub> + H<sub>2</sub>O<sub>2</sub> → H<sub>2</sub>SeO<sub>4</sub>
To obtain the [[anhydrous]] acid as a crystalline solid, the resulting solution is evaporated at temperatures<140 °C in vacuum.<ref name=Seppelt>Seppelt, K. “Selenoyl difluoride” Inorganic Syntheses, 1980, volume XX, pp. 36-38. ISBN 0-471-07715-1. The report describes the synthesis of selenic acid.</ref>
Like [[sulfuric acid]], selenic acid is a strong acid that is hygroscopic and extremely soluble in water. Concentrated solutions are viscous. Crystalline mono- and di-[[water of crystallization|hydrates]] are known. Unlike sulfuric acid, H<sub>2</sub>SeO<sub>4</sub> is a sufficiently strong oxidizer to liberate chlorine from chloride ions, being reduced to [[selenious acid]] (selenic [IV] acid).
Selenic acid reacts with barium salts to precipitate BaSeO<sub>4</sub>, analogous to the sulfate. Calcium selenate is however more soluble than the [[sulfate]].
Treatment of selenic acid with [[fluorosulfuric acid]] gives the dioxydifluoride (b.p. -8.4C):<ref name=Seppelt/>
:H<sub>2</sub>SeO<sub>4</sub> + 2 HO<sub>3</sub>SF → SeO<sub>2</sub>F<sub>2</sub> + 2 H<sub>2</sub>SO<sub>4</sub>
Hot selenic acid is capable of dissolving gold.
==References==
{{reflist}}
[[Category:Selenates]]
[[Category:Acids]]
{{inorganic-compound-stub}}
[[cs:Kyselina selenová]]
[[de:Selensäure]]
[[fr:acide sélénique]]
[[it:Acido selenico]]
[[nl:Seleenzuur]]
[[ja:セレン酸]]
[[pl:Kwas selenowy(VI)]]
[[ru:Селеновая кислота]]
[[vi:Axít selenic]]