Sulfurous Acid - H2SO3

What is Sulfurous Acid?

H2SO3 is a chemical compound with chemical name Sulfurous Acid.

Sulfurous acid 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

H2SO3 Sulfurous acid
Molecular weight of H2SO3 82.07 g/mol
No. of hydrogen bond acceptor 4
Monoisotopic mass of Sulfurous Acid 81.97 g/mol
No. of hydrogen bond donor 2

Sulfurous Acid Structure – H2SO3

Sulfurous Acid structure

Sulfurous Acid Structure – H2SO3

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.

Frequently Asked Questions

What is sulphurous acid used for?

The sulphuric acid is a solid, dibasic acid. It reacts with bases to form salts of bisulfite and sulfite. Uses: Sulphuric acid and its salts are used as effective reducers and disinfectants. This is also used as a mild bleaching agent in applications where chlorine sensitive materials are present.

Is sulphurous acid a strong or weak acid?

Unlike sulphuric acid (H2SO4), sulphuric acid (H2SO3) is a weak acid; that is, aqueous sulphuric acid does not dissociate entirely into H+ (H3O+) and bisulfite ions, meaning that the bisulfite ion is comparatively stronger in maintaining a proton when there is a base, such as water.

Is sulphurous acid dangerous?

Sulphuric acid can affect you by breathing in and moving through your skin. Sulphurous acid is a corrosive substance, so contact with potential eye damage can seriously irritate so burn the skin and eyes. Breathing Sulphuric Acid can irritate the neck and throat.

Is Sulphur a Monoprotic acid?

No monoprotic acid does exist. There are two hydrogen protons in the starting state, sulphuric acid (H2SO4), In other words, the sulfate molecule was bound to certain acidic protons. Note also that monoprotic acids will contribute just one acidic proton, not two as in this acid.

Is sulphurous acid soluble?

It is a colourless gas that has a high solubility in water. In solution, it hydrates to sulphuric acid (H2SO3), which in turn dissociates to form ions of bisulfite (and sulfite (SO2–3).

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

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