Bisulfite ion (
IUPAC-recommended nomenclature: hydrogen sulfite) is the ion HSO3−. Salts containing the HSO3− ion are termed bisulfites also known as sulfite lyes. For example, sodium bisulfiteis NaHSO3.
Bisulfite salts are typically prepared by treatment of alkaline solutions with excess
sulfur dioxide::SO2 + NaOH → NaHSO3
HSO3− is the
conjugate baseof sulfurous acid, H2SO3::H2SO3 unicode|⇌ HSO3− + H+Sulfurous acid is not an isolable compound and does not appear to exist in solution either. An equilibrium that is much more consistent with spectroscopic evidence is given ::SO2 + H2O unicode|⇌ HSO3− + H+
HSO3− is a weakly acidic species with a p"K"a of 6.97. Its conjugate base is the
sulfiteion, SO32−::HSO3− unicode|⇌ SO32− + H+
Most evidence suggests that the proton in bisulfite ion is located on sulfur, giving rise to "C"3v symmetry. There is, however, some evidence from 17O NMR spectroscopy to suggest that two tautomeric forms of HSO3− exist in dynamic equilibrium, one having "C"3v symmetry (protonated at sulfur) and other "C"s symmetry (protonated at oxygen) [D. A. Horner, R. E. Connick, "Inorg. Chem." 25, 2414-7 (1986).] . The "C"3v structure is supported by
X-ray crystallographyand, in aqueous solution, by Raman spectroscopy(ν(S–H) = 2500 cm−1).
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