Interactive image Tautomer: Interactive image ChEMBL1161699 Y InChI=1S/H2O3S/c1-4(2)3/h(H2,1,2,3) Y Key: LSNNMFCWUKXFEE-UHFFFAOYSA-N Y InChI=1/H2O3S/c1-4(2)3/h(H2,1,2,3) Key: LSNNMFCWUKXFEE-UHFFFAOYAJ Tautomer: O[S+](O)[O-] Sulfurous acid ( United Kingdom spelling: sulphurous acid ) is the chemical compound with the formula H 2 SO 3 . Raman spectra of solutions of sulfur dioxide in water show only signals due to the SO 2 molecule and the bisulfite ion, HSO 3 − . [ 2 ] The intensities of the signals are consistent with the following equilibrium : 17 O NMR spectroscopy provided evidence that solutions of sulfurous acid and protonated sulfites contain a mixture of isomers, which is in equilibrium: [ 3 ] Attempts to concentrate the solutions of sulfurous acid simply reverse the equilibrium, producing sulfur dioxide and water vapor. A clathrate with the formula 4SO 2 · 23H 2 O has been crystallised. It decomposes above 7 °C. History and production Sulfurous acid is commonly known not to exist in its free state, and owing to this, it is stated in textbooks that it cannot be isolated in the water-free form. [ 4 ] However, the molecule has been detected in the gas phase in 1988 by the dissociative ionization of diethyl sulfite . [ 5 ] The conjugate bases of this elusive acid are, however, common anions, bisulfite (or hydrogen sulfite) and sulfite . Sulfurous acid is an intermediate species in the formation of acid rain from sulfur dioxide. [ 6 ] Aqueous solutions of sulfur dioxide, which sometimes are referred to as sulfurous acid, are used as reducing agents and as disinfectants, as are solutions of bisulfite and sulfite salts. They are oxidised to sulfuric acid or sulfate by accepting another oxygen atom. [ 7 ] Sulfite paper pulp process ↑ Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution . IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 217. ISBN 0-08-029214-3 . LCCN 82-16524 . ↑ Jolly, William L. (1991). Modern Inorganic Chemistry (2nd ed.). New York: McGraw-Hill. ISBN 0-07-032768-8 .

↑ Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition . Pearson. p. 520. ISBN 978-0-13-175553-6 . ↑ Greenwood, Norman N. ; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 719. doi : 10.1016/C2009-0-30414-6 . ISBN 978-0-08-037941-8 . ↑ D. Sülzle; M. Verhoeven; J. K. Terlouw; H. Schwarz (1988). "Generation and Characterization of Sulfurous Acid (H 2 SO 3 ) and of Its Radical Cation as Stable Species in the Gas Phase". Angew. Chem. Int. Ed. Engl. 27 (11): 1533– 4. doi : 10.1002/anie.198815331 . ↑ McQuarrie; Rock (1987). General Chemistry (2nd ed.). New York: W.H. Freeman and Company. p. 243. ISBN 0-7167-1806-5 . ↑ L. Kolditz, Anorganische Chemie , VEB Deutscher Verlag der Wissenschaften, Berlin 1983, S. 476. H 2 CrO 4 / H 2 Cr 2 O 7 Sulfur oxoacids Hypothetical chemical compounds Articles with short description Short description matches Wikidata Chemical articles with multiple compound IDs Multiple chemicals in an infobox that need indexing ECHA InfoCard ID from Wikidata Chembox having GHS data Articles containing unverified chemical infoboxes Chembox image size set