Bisulfit

Bisulfit, also known as hydrogen sulfite, is an anion with the chemical formula HSO₃⁻. It is an intermediate species in the reduction of sulfur dioxide in aqueous solution and is a strong reducing agent. Bisulfite is formed when sulfur dioxide dissolves in water, producing sulfurous acid (H₂SO₃). This acid then partially dissociates to form the bisulfite ion and a proton. The equilibrium involved is: SO₂ + H₂O ⇌ H₂SO₃ ⇌ H⁺ + HSO₃⁻.

Bisulfite ions are important in various chemical and biological processes. In industry, they are used in processes such as pulp and paper manufacturing as bleaching agents and in the treatment of wastewater to remove chlorine. In food preservation, bisulfites are sometimes used as antioxidants and preservatives, although their use is regulated due to potential allergic reactions in sensitive individuals. They can prevent browning in fruits and vegetables and inhibit microbial growth.

In biological systems, bisulfite can be involved in sulfur metabolism. It can also react with biomolecules, which is the basis for both its beneficial and harmful effects. The reactivity of the bisulfite ion stems from the sulfur atom, which can undergo oxidation. Its reducing properties are widely exploited in chemical synthesis and analytical chemistry. The presence and concentration of bisulfite can be determined through various analytical techniques.