Selenious acid

Selenous acid

Names
IUPAC name Selenous acid
Identifiers
CAS Number	7783-00-8 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:26642 Y
ChemSpider	1060 Y
ECHA InfoCard	100.029.067
KEGG	D05814 Y
PubChem	1091
UNII	F6A27P4Q4R Y
InChI InChI=1S/H2O3Se/c1-4(2)3/h(H2,1,2,3) Y Key: MCAHWIHFGHIESP-UHFFFAOYSA-N Y InChI=1/H2O3Se/c1-4(2)3/h(H2,1,2,3) Key: MCAHWIHFGHIESP-UHFFFAOYAW
SMILES O=[Se](O)O
Properties
Chemical formula	H2SeO3
Molar mass	128.97 g/mol
Appearance	white hygroscopic crystals
Density	3.0 g/cm3
Melting point	decomposes at 70°C
Solubility in water	very soluble
Solubility	soluble in ethanol
Acidity (pKa)	2.46, 7.3
Magnetic susceptibility (χ)	−45.4·10−6 cm3/mol
Related compounds
Other anions	selenic acid hydrogen selenide
Other cations	sodium selenite
Related compounds	sulfurous acid tellurous acid polonous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
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.

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:

It is moderately oxidizing in nature, but kinetically slow. In 1 M H+
:

In 1 M OH−
:

It is used in organic synthesis for the synthesis of 1,2-diketones (e.g. glyoxal).

The major use is in protecting and changing the color of steel, especially steel parts on firearms. The so-called cold-bluing process uses selenous acid, copper(II) nitrate, and nitric acid to change the color of the steel from silver-grey to blue-grey or black. Alternative procedures use copper sulfate and phosphoric acid instead. This process deposits a coating of copper selenide and is fundamentally different from other bluing processes which generate black iron oxide. Some older razor blades were also made of blued steel.