Sulfurous acid
is the chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 H₂SO₃. 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

Bisulfite

Bisulfite ion is the ion HSO3−. Salts containing the HSO3− ion are termed bisulfites also known as sulfite lyes...

 (or hydrogensulfite) and sulfite

Sulfite

Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...

.

Raman spectra

Raman spectroscopy

Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...

 of solutions of sulfur dioxide

Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 in water show only signals due to the SO₂ molecule and the bisulfite ion, HSO₃⁻. The intensities of the signals are consistent with the following equilibrium

Chemical equilibrium

In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

:

SO₂ + H₂O HSO₃⁻ + H⁺

K_a = 1.54; pK_a = 1.81.

Aqueous solutions of sulfur dioxide, which sometimes are referred to as sulfurous acid are used as reducing agents

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 and as disinfectants, as are solutions of bisulfite and sulfite salts. They are also mild bleach

Bleach

Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...

es, and are used for materials which may be damaged by chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

-containing bleaches.

See also

• Bisulfite
  Bisulfite
  Bisulfite ion is the ion HSO3−. Salts containing the HSO3− ion are termed bisulfites also known as sulfite lyes...
  
  
• Carbonic acid
  Carbonic acid
  Carbonic acid is the inorganic compound with the formula H2CO3 . It is also a name sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3. Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates...
  
  
• Pulp (paper)
• Sulfite paper pulp process
  Sulfite process
  The sulfite process produces wood pulp which is almost pure cellulose fibers by using various salts of sulfurous acid to extract the lignin from wood chips in large pressure vessels called digesters. The salts used in the pulping process are either sulfites , or bisulfites , depending on the pH...
  
  
• Sulfite
  Sulfite
  Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...
  
  
• Sulfuric acid
  Sulfuric acid
  Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...