Sulfurous acid (also sulfuric(IV) acid, sulphurous acid (UK), sulphuric(IV) acid (UK)) is the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the
formula . There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase. 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.
Raman spectra of solutions of
sulfur dioxide in water show only signals due to the molecule and the bisulfite ion, . The intensities of the signals are consistent with the following
equilibrium:
17O
NMR spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic fie ...
provided evidence that solutions of sulfurous acid and protonated sulfites contain a mixture of isomers, which is in equilibrium:
Attempts to concentrate the solutions of sulfurous acid simply reverses the equilibrium, producing sulfur dioxde and water vapor. A
clathrate with the formul a has been crystallised. It decomposes above 7 °C. Anhydrous sulfurous acid has not been isolated.
Uses
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
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
by accepting another
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
atom.
[L. Kolditz, ''Anorganische Chemie'', VEB Deutscher Verlag der Wissenschaften, Berlin 1983, S. 476.]
See also
*
Bisulfite
*
Carbonic acid
*
Pulp (paper)
*
Sulfite paper pulp process
*
Sulfite
*
Sulfuric acid
References
{{Authority control
Hydrogen compounds
Sulfites
Sulfur oxoacids