Selenic acid
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Names | |||
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IUPAC name
Selenic(VI) acid
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Other names
Selenic acid
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Identifiers | |||
3D model (
JSmol ) |
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ChEBI | |||
ChemSpider | |||
ECHA InfoCard
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100.029.072 | ||
EC Number |
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KEGG | |||
PubChem CID
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RTECS number
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UNII | |||
UN number | 1905 | ||
CompTox Dashboard (EPA)
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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
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Biselenate | ||
−51.2·10−6 cm3/mol | |||
Refractive index (nD)
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1.5174 (D-line, 20 °C) | ||
Structure | |||
tetrahedral at Se | |||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards
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Corrosive, highly toxic | ||
GHS labelling:[2] | |||
Danger | |||
H301, H315, H318, H331, H373, H410 | |||
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) | |||
Related compounds | |||
Other anions
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selenious acid
hydrogen selenide | ||
Other cations
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sodium selenate potassium selenate | ||
Related compounds
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Selenic acid is the
Structure and bonding
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
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
Like
Selenic acid is a stronger
- 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
Selenic acid is used as a specialized oxidizing agent.
References
- ISBN 9781439826232.
- ^ "Selenic acid". pubchem.ncbi.nlm.nih.gov. Retrieved 16 December 2021.
- .
- ^ ISBN 978-1-4067-7302-6.
- ISBN 978-0-85404-366-8.
- ^ ISBN 81-224-1384-6.
- .
- ^ ISBN 0-471-07715-1. The report describes the synthesis of selenic acid.
- ISBN 978-0-08-037941-8.
- .