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| Names | |||
|---|---|---|---|
| IUPAC name Selenic(VI) acid | |||
| Other names Selenic acid | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChEBI | |||
| ChemSpider |
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| ECHA InfoCard | 100.029.072 | ||
| EC Number |
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| KEGG |
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| RTECS number |
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| UNII | |||
| UN number | 1905 | ||
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| Properties | |||
| H2SeO4 | |||
| Molar mass | 144.9734 g/mol | ||
| Appearance | Colorless deliquescent crystals | ||
| Density | 2.95 g/cm3, solid | ||
| Melting point | 58 °C (136 °F; 331 K) | ||
| Boiling point | 260 °C (500 °F; 533 K) (decomposes) | ||
| 130 g/(100 mL) (30 °C) | |||
| Acidity (pKa) | pKa1 = −3 pKa2 = 1.9[1] | ||
| Conjugate base | Biselenate | ||
| −51.2·10−6 cm3/mol | |||
Refractive index (nD) | 1.5174 (D-line, 20 °C) | ||
| Structure | |||
| tetrahedral at Se | |||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards | Corrosive, highly toxic | ||
| GHS labelling:[2] | |||
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| Danger | |||
| H301,H315,H318,H331,H373,H410 | |||
| P260,P264,P270,P271,P273,P280,P301+P310,P302+P352,P304+P340,P305+P351+P338,P310,P311,P314,P321,P330,P332+P313,P362,P391,P403+P233,P405,P501 | |||
| NFPA 704 (fire diamond) | |||
| Related compounds | |||
Otheranions | selenious acid hydrogen selenide | ||
Othercations | sodium selenate potassium selenate | ||
Related compounds | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Selenic acid is theinorganic compound with theformulaH2SeO4. It is anoxoacid ofselenium, and its structure is more accurately described asO2Se(OH)2. It is a colorless compound. Although it has few uses, one of its salts,sodium selenate is used in the production of glass and animal feeds.[3]
The molecule is tetrahedral, as predicted byVSEPR theory. The Se–O bond length is 161 pm.[4] In the solid state, it crystallizes in anorthorhombic structure.[5]
It is prepared by oxidising selenium compounds in lower oxidation states. One method involves the oxidation ofselenium dioxide withhydrogen peroxide:
Unlike the productionsulfuric acid by hydration ofsulfur trioxide, the hydration ofselenium trioxide is an impractical method.[4] Instead, selenic acid may also be prepared by the oxidation ofselenous acid (H2SeO3) with halogens, such aschlorine orbromine, or withpotassium permanganate.[6] Using chlorine or bromine as the oxidising agents also produces hydrochloric or hydrobromic acid as a side-product, which needs to be removed from the solution since they can reduce the selenic acid to selenous acid.[7]
To obtain theanhydrous acid as a crystalline solid, the resulting solution is evaporated at temperatures below 140 °C (413 K; 284 °F) in a vacuum.[8]
Likesulfuric acid, selenic acid is astrong acid that ishygroscopic and extremely soluble in water. Concentrated solutions are viscous. Crystalline mono- and di-hydrates are known.[6] The monohydrate melts at 26 °C, and the dihydrate melts at −51.7 °C.[4]
Selenic acid is a strongeroxidizer thansulfuric acid,[9] capable of liberatingchlorine fromchloride ions, being reduced toselenous acid in the process:
It decomposes above 200 °C, liberating oxygen gas and being reduced toselenous acid:[6]
Selenic acid reacts with barium salts to precipitate solidBaSeO4, analogous to the sulfate. In general, selenate salts resemble sulfate salts, but are more soluble. Many selenate salts have the same crystal structure as the corresponding sulfate salts.[4]
Treatment withfluorosulfuric acid givesselenoyl fluoride:[8]
Hot, concentrated selenic acid reacts withgold, forming a reddish-yellow solution of gold(III) selenate:[10]
Selenic acid is used as a specialized oxidizing agent.
