Selenous acid
| Structural formula | |
| Ball-and-stick model | |
| Names | |
|---|---|
| IUPAC name
Selenous acid
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| Identifiers | |
7783-00-8  |
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| ChEBI | CHEBI:26642 |
| ChemSpider | 1060 |
| Jmol 3D model | Interactive image |
| KEGG | D05814 |
| PubChem | 1091 |
| UNII | F6A27P4Q4R |
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| Properties | |
| H2SeO3 | |
| Molar mass | 128.97 g/mol |
| Appearance | white hygroscopic crystals |
| Density | 3.0 g/cm3 |
| Melting point | decomposes at 70°C |
| very soluble | |
| Solubility | soluble in ethanol |
| Acidity (pKa) | 2.46, 7.3[2] |
| Vapor pressure | {{{value}}} |
| Related compounds | |
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Other anions
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selenic acid hydrogen selenide |
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Other cations
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sodium selenite |
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Related compounds
|
sulfurous acid tellurous acid polonous acid |
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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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| Infobox references | |
Selenous acid (or selenious acid) is the chemical compound with the formula H2SeO3. Structurally, it is more accurately described by (HO)2SeO. It is the principal oxoacid of selenium; the other being selenic acid.
Formation and properties
Selenous acid is analogous to sulfurous acid, but it is more readily isolated. Selenous acid is easily formed upon the addition of selenium dioxide to water. As a crystalline solid, the compound can be seen as pyramidal molecules that are interconnected with hydrogen bonds. In solution it is a diprotic acid:[3]
- H
2SeO
3 ⇌ H+
+ HSeO−
3 (pKa = 2.62) - HSeO−
3 ⇌ H+
+ SeO2−
3 (pKa = 8.32)
It is moderately oxidizing in nature, but kinetically slow. In 1 M H+
:
- H
2SeO
3 + 4 H+
+ 4 e− ⇌ Se + 3 H
2O (Eo= +0.74 V)
In 1 M OH−
:
- SeO2−
3 + 4 e− + 3 H
2O ⇌ Se + 6 OH−
(Eo= −0.37 V)
It is used in organic synthesis for the synthesis of 1,2-diketones (e.g. glyoxal).[4]
Uses
The major use is in changing the color of steel, especially the steel in guns, the so-called "bluing" process which uses selenous acid, copper(II) nitrate, and nitric acid to change the color of the steel from silver-grey to blue-grey. Some older razor blades were also made of blued steel.[5]
Another use for selenious acid is the chemical darkening and patination of copper, brass and bronze, producing a rich dark brown color that can be further enhanced with mechanical abrasion.[citation needed]
It can be use used as an oxidizing agent e.g. in laboratory preparation of glyoxal (ethane-1,2-dione) from glycol.
Selenious acid is a key component of the Mecke reagent used for drug testing.[6]
Health effects
Like many selenium compounds, selenous acid is highly toxic in excessive quantities, and ingestion of any significant quantity of selenous acid is usually fatal, however it is an approved dietary source in proper amounts. Symptoms of selenium poisoning can occur several hours after exposure, and may include stupor, nausea, severe hypotension and death.[7]
References
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ http://www2.ucdsb.on.ca/tiss/stretton/database/polyprotic_acids.htm
- ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ↑ “Glyoxal Bisulfite”, Organic Syntheses, Collected Volume 3, p.438 (1955).
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ MSDS for "Reagent for Special Opiates (Codeine, Heroin, & Morphine)", Sirchie Finger Print Laboratories, Inc. May 12, 2006. (The page cannot be found)
