Selenic acid 2256072 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]]