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Disulfurous acid, metabisulfurous acid or pyrosulfurous acid is an oxoacid of 
sulfur
Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
with the formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...
. Its structure is . The salt
In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
s of disulfurous acid are called disulfites or metabisulfites. Disulfurous acid is, like sulfurous acid
Sulfuric(IV) acid (United Kingdom spelling: sulphuric(IV) acid), also known as sulfurous (UK: sulphurous) acid and thionic acid, is the chemical compound with the chemical formula, formula .
Raman spectroscopy, Raman spectra of solutions o ...
(), a phantom acid, which does not exist in the free state. In contrast to disulfate (), disulfite has two directly connected sulfur atoms. The oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...
of the sulfur atom bonded to three oxygen atoms is +5 and its valence is 6, while that of the other sulfur is +3 and 4 respectively.
References
Sulfur oxoacids Metabisulfites Hypothetical chemical compounds {{acid-stub