Disulfurous acid

Disulfurous acid or pyrosulfurous acid is an oxoacid of sulfur with the formula H₂S₂O₅. The salts of disulfurous acid are called disulfites or metabisulfites. Disulfurous acid is, like sulfurous acid (H₂SO₃), a phantom acid, which does not exist in the free state. In contrast to disulfate (S₂O₇⁻), disulfite has two directly connected sulfur atoms. The oxidation state of the sulfur atom bonded to 3 oxygen atoms is +5 while oxidation number of other sulfur atom is +3.