Selenous acid
Encyclopedia
Selenous 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
.
, 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 bond
s. In solution it is a diprotic acid:
It is moderately oxidizing in nature, but kinetically slow. In 1 M :
In 1 M :
It is used in organic synthesis
for the synthesis of 1,2-diketone
s (e.g. glyoxal
).
, 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.
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.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
H2SeO3. Structurally, it is more accurately described by (HO)2SeO. It is the principal oxoacid
Oxoacid
An oxoacid is an acid that contains oxygen. To be more specific, it is an acid that:#contains oxygen#contains at least one other element#has at least one hydrogen atom bound to oxygen#forms an ion by the loss of one or more protons....
of selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
; the other being selenic acid
Selenic acid
Selenic acid is the chemical compound with the formula . It is an oxoacid of selenium, and its structure is more accurately described as .As predicted by VSEPR theory, the selenium center is tetrahedral, with a Se–O bond length of 161 pm...
.
Formation and properties
Selenous acid is analogous to sulfurous acidSulfurous acid
Sulfurous acid is the chemical compound with the formula H2SO3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase...
, but it is more readily isolated. Selenous acid is easily formed upon the addition of selenium dioxide
Selenium dioxide
Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium.-Properties:...
to water. As a crystalline solid, the compound can be seen as pyramidal molecules that are interconnected with hydrogen bond
Hydrogen bond
A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen, oxygen or fluorine, that comes from another molecule or chemical group. The hydrogen must be covalently bonded to another electronegative atom to create the bond...
s. In solution it is a diprotic acid:
- + (pKa = 2.62)
- + (pKa = 8.32)
It is moderately oxidizing in nature, but kinetically slow. In 1 M :
- + 4 + 4 Se + 3 (E
o= +0.74 V)
In 1 M :
- + 4 + 3 Se + 6 (E
o= −0.37 V)
It is used in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
for the synthesis of 1,2-diketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s (e.g. glyoxal
Glyoxal
Glyoxal is an organic compound with the formula OCHCHO. This yellow colored liquid is the smallest dialdehyde . Its tautomer acetylenediol is unstable.-Production:...
).
Uses
The major use is in changing the color of steel, especially the steel in guns, the so-called "blueing" process which uses selenous acid, copper(II) nitrateCopper(II) nitrate
Copper nitrate is the chemical compound with the formula Cu2. Commonly referred to simply as copper nitrate, the anhydrous form is a blue, crystalline solid...
, and nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
to change the color of the steel from silver-grey to blue-grey. Some older razor blades were also made of blued steel.
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.