English

Alternative spellings

• bisulphite qualifier UK

Noun

1. The univalent group -HSO3, or any salt containing it.

Translations

Derived terms

• metabisulfite
• sodium bisulfite

Bisulfite ion (IUPAC-recommended nomenclature: hydrogen sulfite) is the ion HSO3−. Salts containing the HSO3− ion are termed bisulfites. For example, sodium bisulfite is NaHSO3.

Reactions

Bisulfite salts are typically prepared by treatment of alkaline solutions with excess sulfur dioxide:

SO2 + NaOH → NaHSO3

HSO3− is the conjugate base of sulfurous acid, H2SO3:

H2SO3 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 HSO3− + H+

HSO3− is a weakly acidic species with a pKa of 6.97. Its conjugate base is the sulfite ion, SO32−:

HSO3− SO32− + H+

Structure

Most evidence suggests that the proton in bisulfite ion is located on sulfur, giving rise to C3v symmetry. There is, however, some evidence from 17O NMR spectroscopy to suggest that two tautomeric forms of HSO3− exist in dynamic equilibrium, one having C3v symmetry (protonated at sulfur) and other Cs symmetry (protonated at oxygen). The C3v structure is supported by X-ray crystallography and, in aqueous solution, by Raman spectroscopy (ν(S–H) = 2500 cm−1).

References