Selenic acid
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Selenic acid is the inorganic compound with the formula Template:Chem2. It is an oxoacid of selenium, and its structure is more accurately described as Template:Chem2. 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.[2]
Structure and bonding
The molecule is tetrahedral, as predicted by VSEPR theory. The Se–O bond length is 161 pm.[3] In the solid state, it crystallizes in an orthorhombic structure.[4]
Preparation
It is prepared by oxidising selenium compounds in lower oxidation states. One method involves the oxidation of selenium dioxide with hydrogen peroxide:
Unlike the production sulfuric acid by hydration of sulfur trioxide, the hydration of selenium trioxide is an impractical method.[3] Instead, selenic acid may also be prepared by the oxidation of selenous acid (Template:Chem2) with halogens, such as chlorine or bromine, or with potassium permanganate.[5] 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.[6]
To obtain the anhydrous acid as a crystalline solid, the resulting solution is evaporated at temperatures below Script error: No such module "convert". in a vacuum.[7]
Reactions
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-hydrates are known.[5] The monohydrate melts at 26 °C, and the dihydrate melts at −51.7 °C.[3]
Selenic acid is a stronger oxidizer than sulfuric acid,[8] capable of liberating chlorine from chloride ions, being reduced to selenous acid in the process:
It decomposes above 200 °C, liberating oxygen gas and being reduced to selenous acid:[5]
Selenic acid reacts with barium salts to precipitate solid Template:Chem2, 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.[3]
Treatment with fluorosulfuric acid gives selenoyl fluoride:[7]
Hot, concentrated selenic acid reacts with gold, forming a reddish-yellow solution of gold(III) selenate:[9]
Applications
Selenic acid is used as a specialized oxidizing agent.
References
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- ↑ Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. Script error: No such module "CS1 identifiers"..
- ↑ a b c d Script error: No such module "citation/CS1".
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- ↑ a b Seppelt, K. “Selenoyl Difluoride” Inorganic Syntheses, 1980, volume XX, pp. 36-38. Template:ISBN. The report describes the synthesis of selenic acid.
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