Sulfurous Acid - H2SO3

What is Sulfurous Acid?

H2SO3 is a chemical compound with chemical name Sulfurous Acid. It is also called Sulfur dioxide solution or dihydrogen trioxosulfate or trioxosulfuric acid. It is an intermediate species to produce acid rain from sulfur dioxide (SO2).

Trioxosulfuric acid is a liquid without colour and has a pungent burning sulfur smell. It is corrosive to tissue and metals. It is a sulfur oxoacid, tautomer of a sulfonic acid, and conjugate acid of a hydrogensulfite.

Properties of Sulfurous Acid – H2SO3


Sulfurous acid

Molecular weight of H2SO3

82.07 g/mol

No. of hydrogen bond acceptor


Monoisotopic mass of Sulfurous Acid

81.97 g/mol

No. of hydrogen bond donor


Sulfurous Acid structure – H2SO3

Sulfurous Acid structure

H2SO3 Uses (Sulfurous Acid)

  • Sulfurous Acid is used as an intermediate in industries.
  • Used as reducing agents.
  • Used as disinfectants.
  • Used in the manufacturing of paper products.


According to Raman spectra of SO2 solutions shows that the intensities of the signals are consistent with the equilibrium as follows:

SO2 + H2O ⇌ HSO3 + H+

where , Ka = 1.54×10−2 and pKa = 1.81.

Health hazards

It is a toxic, corrosive, and non-combustible compound. Inhaling, ingesting or skin contact with Sulfur dioxide solution causes severe injury which leads to death. In its molten form it can cause severe burns to eyes and skin. Therefore avoid skin contact with this compound. On this compound it liberates corrosive, toxic and irritating gases.

Learn more about the Structure, physical and chemical properties of H2SO3 from the experts at BYJU’S.

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