Sulfurous acid
General
Systematic name	Sulfurous acid
Molecular formula	H2SO3 (aq)
Molar mass	82.07 g/mol
Properties
Acid dissociation constant pKa	1.81 (18°C) 1 6.91 (18°C) 2
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Sulfurous acid (or sulphurous acid in British spelling) is a name given to aqueous solutions of sulfur dioxide. There is no evidence that the sulfurous acid molecule, H₂SO₃, exists in these solutions. They cannot be isolated as a pure substance, because boiling the sulphurous acid will drive away sulphur dioxide, leaving water. They react with alkalis to form bisulfite (or hydrogensulfite) and sulfite salts. Image File history File links Sulfurous_acid. ... IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... In chemistry and biochemistry, the acid dissociation constant, the acidity constant, or the acid-ionization constant (Ka) is a specific type of equilibrium constant that indicates the extent of dissociation of hydrogen ions from an acid. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... This article describes water from a scientific and technical perspective. ... Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... In chemistry, an alkali (from Arabic: al-qaly) is a basic, ionic salt of an alkali metal or alkali earth metal element. ... The bisulfite ion is the HSO3- ion. ...

Raman spectra of solutions of sulfur dioxide 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: Raman spectroscopy is a spectroscopic technique used in condensed matter physics and chemistry to study vibrational, rotational, and other low-frequency modes in a system. ... Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ...

SO₂ + H₂O ⇌ HSO₃⁻ + H⁺

K_a = 1.54x10⁻² L/mol; pK_a = 1.81.

The hydrogen atom in the bisulfite ion is bonded to the sulfur atom and not to an oxygen atom as is more usual in the case of oxoanions. This has been shown in the solid state by X-ray crystallography and in aqueous solution by Raman spectroscopy (ν(S–H) = 2500 cm⁻¹). It is, however, acidic according to the following equilibrium: General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Atomic mass 32. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... An oxyanion or oxoanion is a negatively charged polyatomic ion that contains oxygen. ... X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of X-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. ... Raman spectroscopy is a spectroscopic technique used in condensed matter physics and chemistry to study vibrational, rotational, and other low-frequency modes in a system. ...

HSO₃⁻ ⇌ SO₃²⁻ + H⁺

K_a = 1.02x10⁻⁷ L/mol; pK_a = 6.97.

Solutions of sulfur dioxide ("sulfurous acid") and of bisulfite and sulfite salts are used as reducing agents and as disinfectants. They are also mild bleaches, and are used for materials which may be damaged by chlorine-containing bleaches. Semi-accurate illustration of a redox reaction Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... For the anime/manga see Bleach (manga) For other uses, see Bleach (disambiguation). ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ...

See also

• Sulfite
• Sulfuric acid
• Bisulfite

Sulfites (also sulphite) are compounds that contain the sulfite ion SO32-. They are often used as preservatives in wines (to prevent spoilage and oxidation), dried fruits, and dried potato products. ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... The bisulfite ion is the HSO3- ion. ...

External links

• Links to external chemical sources.