Selenic Acid - Wikipedia

Selenic acid

Names
IUPAC name Selenic(VI) acid
Other names Selenic acid
Identifiers
CAS Number	7783-08-6 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:18170 Y
ChemSpider	1058 Y
ECHA InfoCard	100.029.072
EC Number	231-979-4
KEGG	C05697 Y
PubChem CID	1089
RTECS number	VS6575000
UNII	HV0Y51NC4J Y
UN number	1905
CompTox Dashboard (EPA)	DTXSID2064818
InChI InChI=1S/H2O4Se/c1-5(2,3)4/h(H2,1,2,3,4) YKey: QYHFIVBSNOWOCQ-UHFFFAOYSA-N Y InChI=1/H2O4Se/c1-5(2,3)4/h(H2,1,2,3,4)Key: QYHFIVBSNOWOCQ-UHFFFAOYAI
SMILES O[Se+2]([O-])([O-])O
Properties
Chemical formula	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)
Solubility in water	130 g/(100 mL) (30 °C)
Acidity (pKa)	pKa1 = −3pKa2 = 1.9[1]
Conjugate base	Biselenate
Magnetic susceptibility (χ)	−51.2·10−6 cm3/mol
Refractive index (nD)	1.5174 (D-line, 20 °C)
Structure
Molecular shape	tetrahedral at Se
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Corrosive, highly toxic
GHS labelling:[2]
Pictograms
Signal word	Danger
Hazard statements	H301, H315, H318, H331, H373, H410
Precautionary statements	P260, P261, 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)	3 0 2OX
Related compounds
Other anions	selenious acidhydrogen selenide
Other cations	sodium selenatepotassium selenate
Related compounds	Sulfuric acid Selenium dioxide Selenium trioxide Telluric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Chemical compound

Selenic acid is the inorganic compound with the formula H2SeO4. It is an oxoacid of selenium, and its structure is more accurately described as O2Se(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]

Structure and bonding

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The molecule is tetrahedral, as predicted by VSEPR theory. The Se–O bond length is 161 pm.[4] In the solid state, it crystallizes in an orthorhombic structure.[5]

Preparation

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It is prepared by oxidising selenium compounds in lower oxidation states. One method involves the oxidation of selenium dioxide with hydrogen peroxide:

SeO2 + H2O2 → H2SeO4

Unlike the production sulfuric acid by hydration of sulfur trioxide, the hydration of selenium trioxide is an impractical method.[4] Instead, selenic acid may also be prepared by the oxidation of selenous acid (H2SeO3) with halogens, such as chlorine or bromine, or with potassium 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 the anhydrous acid as a crystalline solid, the resulting solution is evaporated at temperatures below 140 °C (413 K; 284 °F) in a vacuum.[8]

Reactions

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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.[6] The monohydrate melts at 26 °C, and the dihydrate melts at −51.7 °C.[4]

Selenic acid is a stronger oxidizer than sulfuric acid,[9] capable of liberating chlorine from chloride ions, being reduced to selenous acid in the process:

H2SeO4 + 2 H+ + 2 Cl− → H2SeO3 + H2O + Cl2

It decomposes above 200 °C, liberating oxygen gas and being reduced to selenous acid:[6]

2 H2SeO4 → 2 H2SeO3 + O2

Selenic acid reacts with barium salts to precipitate solid BaSeO4, 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 with fluorosulfuric acid gives selenoyl fluoride:[8]

H2SeO4 + 2 HSO3F → SeO2F2 + 2 H2SO4

Hot, concentrated selenic acid reacts with gold, forming a reddish-yellow solution of gold(III) selenate:[10]

2 Au + 6 H2SeO4 → Au2(SeO4)3 + 3 H2SeO3 + 3 H2O

Applications

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Selenic acid is used as a specialized oxidizing agent.

References

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1. ^ Magdi Selim, H. (2011-03-15). Dynamics and Bioavailability of Heavy Metals in the Rootzone. CRC Press. ISBN 9781439826232.
2. ^ "Selenic acid". pubchem.ncbi.nlm.nih.gov. Retrieved 16 December 2021.
3. ^ Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a23_525.
4. ^ a b c d Don M. Yost (2007). Systematic Inorganic Chemistry. Read Books. pp. 343–346. ISBN 978-1-4067-7302-6.
5. ^ Mathias S. Wickleder (2007). Francesco A. Devillanova (ed.). Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium. Royal Society of Chemistry. p. 353. ISBN 978-0-85404-366-8.
6. ^ a b c Anil Kumar De (2003). A Text Book of Inorganic Chemistry. New Age International. pp. 543–545. ISBN 81-224-1384-6.
7. ^ Lenher, V.; Kao, C. H. (June 1925). "The preparation of selenic acid and of certain selenates". Journal of the American Chemical Society. 47 (6): 1521–1522. doi:10.1021/ja01683a005.
8. ^ a b 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.
9. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 782. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
10. ^ Lenher, V. (April 1902). "Action of selenic acid on gold". Journal of the American Chemical Society. 24 (4): 354–355. doi:10.1021/ja02018a005.

v t e Selenium compounds
Se(−II)	Se2− H2Se Al2Se3 Sb2Se3 As2Se3 Bi2Se3 CdSe CaSe CSe2 OCSe CrSe CoSe CuSe (CH3)2Se GaSe Ga2Se3 GeSe In2Se3 FeSe PbSe MgSe MnSe MnSe2 HgSe MoSe2 NiSe NbSe2 NbSe3 PxSey PuSe ReSe2 Sm2Se3 Ag2Se Na2Se SnSe TiSe2 WSe2 USe2 ZnSe
Se(0,I)	Se3S5
Se(I)	Se2S6 Se2Cl2 C3H7NO2Se
Se(II)	SeBr2 SeCl2 SeS2
Se(III)	Se4N4
Se(IV)	SeO2−3 SeBr4 SeCl4 SeF4 SeO2 SeS2 SeOF2 SeOCl2 SeOBr2 H2SeO3
Se(VI)	SeO2−4 SeF6 SeO3 SeO2F2 H2SeO4
Se(IV,VI)	SeO2−4 + SeO2−3

v t e Hydrogen compounds

H3AsO3 H3AsO4 HArF HAt HSO3F H[BF4] HBr HBrO HBrO2 HBrO3 HBrO4 HCl HClO HClO2 HClO3 HClO4 HCN HCNO H2CrO4/H2Cr2O7 H2CO3 H2CS3 HF HFO HI HIO HIO2 HIO3 HIO4 HMnO4 H2MnO4 H2MoO4 HNC NaHCO3 HNCO HNO HNO2 HNO3 H2N2O2 HNO5S H3NSO3 H2O H2O2 H2O3 H2O4 H2O5 H3PO2 H3PO3 H3PO4 H4P2O7 H5P3O10 H[AuCl4] H2[PtCl6] H2OsCl6 H2S H2S2 H2Se H2SeO3 H2SeO4 H4SiO4 H2[SiF6] HSCN HNCS H2SO3 H2SO4 H2SO5 H2S2O3 H3O H2S2O6 H2S2O7 H2S2O8 CF3SO3H H2Te H2TeO3 H6TeO6 H4TiO4 H2Po H[Co(CO)4]

v t e Salts and covalent derivatives of the selenate ion

H2SeO4 He Li2SeO4 BeSeO4 B C (NH4)2SeO4 O F Ne Na2SeO4 MgSeO4 Al2(SeO4)3 Si P S Cl Ar K2SeO4 CaSeO4 Sc Ti V Cr Mn FeSeO4Fe2(SeO4)3 CoSeO4 NiSeO4 CuSeO4 ZnSeO4 Ga2(SeO4)3 Ge As SeO42- Br Kr Rb2SeO4 SrSeO4 Y Zr(SeO4)2 Nb Mo Tc Ru Rh Pd Ag2SeO4 CdSeO4 In Sn Sb Te I Xe Cs2SeO4 BaSeO4 * Lu2(SeO4)3 Hf(SeO4)2 Ta W Re Os Ir Pt Au2(SeO3)2(SeO4) Hg Tl PbSeO4 Bi Po At Rn Fr Ra ** Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og   * La2(SeO4)3 Ce2(SeO4)3Ce(SeO4)2 Pr2(SeO4)3 Nd2(SeO4)3 Pm Sm2(SeO4)3 Eu2(SeO4)3 Gd2(SeO4)3 Tb Dy2(SeO4)3 Ho2(SeO4)3 Er2(SeO4)3 Tm2(SeO4)3 Yb2(SeO4)3 ** Ac Th(SeO4)2 H3PaO(SeO4)3 UO2SeO4 (NpO2)2SeO4 Pu Am Cm Bk Cf Es Fm Md No