Bisulfite 2870697 210459671 2008-05-06T00:38:32Z PipepBot 4984067 robot Adding: [[it:Bisolfito]] [[Image:Bisulfite-S-H-tautomer-3D-balls.png|thumb|right|200px|A [[ball-and-stick model]] of the most commonly stated structure for the bisulfite ion in solution and in the solid state.]] '''Bisulfite''' ion ([[IUPAC]]-recommended nomenclature: '''hydrogen sulfite''') is the ion HSO<sub>3</sub><sup>−</sup>. Salts containing the HSO<sub>3</sub><sup>−</sup> ion are termed bisulfites. For example, [[sodium bisulfite]] is NaHSO<sub>3</sub>. ==Reactions== Bisulfite salts are typically prepared by treatment of alkaline solutions with excess [[sulfur dioxide]]: :SO<sub>2</sub> + NaOH → NaHSO<sub>3</sub> HSO<sub>3</sub><sup>−</sup> is the [[conjugate base]] of [[sulfurous acid]], H<sub>2</sub>SO<sub>3</sub>: :H<sub>2</sub>SO<sub>3</sub> {{unicode|⇌}} HSO<sub>3</sub><sup>−</sup> + H<sup>+</sup> Sulfurous acid is not an isolable compound and does not appear to exist in solution either. An equilibrium that is much more consistent with [[spectroscopy|spectroscopic]] evidence is given : :SO<sub>2</sub> + H<sub>2</sub>O {{unicode|⇌}} HSO<sub>3</sub><sup>−</sup> + H<sup>+</sup> HSO<sub>3</sub><sup>−</sup> is a weakly acidic species with a [[acid dissociation constant|p''K''<sub>a</sub>]] of 6.97. Its conjugate base is the [[sulfite]] ion, SO<sub>3</sub><sup>2−</sup>: :HSO<sub>3</sub><sup>−</sup> {{unicode|⇌}} SO<sub>3</sub><sup>2−</sup> + H<sup>+</sup> ==Structure== [[Image:Bisulfite-equilibrium-2D.png|300px|thumb|right|Bisulfite tautomers in equilbrium]] [[Image:Bisulfite-equilibrium-3D-balls.png|300px|thumb|right|Ball-and-stick models of the proposed bisulfite equilbrium. The tautomer on the left has ''C''<sub>s</sub> symmetry, while that of the tautomer on the right is ''C''<sub>3v</sub>.]] Most evidence suggests that the proton in bisulfite ion is located on sulfur, giving rise to [[molecular symmetry |''C''<sub>3v</sub> symmetry]]. There is, however, some evidence from [[oxygen-17|<sup>17</sup>O]] [[nuclear magnetic resonance spectroscopy|NMR]] spectroscopy to suggest that two tautomeric forms of HSO<sub>3</sub><sup>−</sup> exist in dynamic equilibrium, one having ''C''<sub>3v</sub> symmetry (protonated at sulfur) and other ''C''<sub>s</sub> symmetry (protonated at oxygen)<ref>D. A. Horner, R. E. Connick, ''Inorg. Chem.'' '''25''', 2414-7 (1986).</ref>. The ''C''<sub>3v</sub> structure is supported by [[X-ray crystallography]] and, in aqueous solution, by [[Raman spectroscopy]] (ν(S–H) = 2500 cm<sup>−1</sup>). ==References== <references/> [[Category:Bisulfites|*]] [[Category:Oxoanions]] {{inorganic-compound-stub}} [[it:Bisolfito]] [[ru:Гидросульфиты]] [[fi:Vetysulfiitti]] [[zh:亚硫酸氢根]]