What is the percentage composition of the element of H₂SO₃?

The correct answer is 2.5% H, 39% S, 58.5% O.

Key Points

•  H2SO3
  • ​It consists of two hydrogen (H) atoms, one sulfur (S) atom, and three oxygen (O) atoms.
  • Pure sulfurous acid is a heavy, colorless liquid that is stable only at low temperatures. However, in practice, sulfurous acid is usually used as an aqueous solution.
  • Sulfurous acid is a weak acid. It can donate two protons (H+ ions) to an aqueous solution.
  • The percentage composition of the element of H2SO3 is  2.5% H, 39% S, 58.5% O.

  • H₂SO₃ => (2 x Atomic mass of hydrogen) + Atomic mass of sulfur + (3 x Atomic mass of oxygen) => (2 x 1) + 32 + (3 x 16) => 2 + 32 + 48 => 82 g/mol

    Calculate the percentage composition:

    Hydrogen: (2 / 82) x 100% = 2.44% approximately equals 2.5%

    Sulfur: (32 / 82) x 100% = 39.02% approximately equals 39%

    Oxygen: (48 / 82) x 100% = 58.53% approximately equals 58.5%

  • It is produced from the reaction of sulfur dioxide (SO₂) with water (H₂O). The non-balanced chemical reaction is: SO₂ + H₂O -> H₂SO₃
  • While not commonly used in its pure form due to instability, it is often used in the form of its salts, known as sulfites. Sulfites are commonly used as preservatives in food and drink to prevent discoloration and prolong shelf life.
  • Sulfurous acid and its salts (sulfites) can cause allergic reactions in some people, particularly in high concentrations, causing symptoms such as breathing difficulties, skin rashes, and digestive problems. As such, usage of sulfites in food and beverages is subject to regulation in many countries.