M2S2O5

M2S2O5 refers to a chemical compound with the empirical formula S2O5^2-. This anion is known as the pyrosulfite or metabisulfite ion. When considering a specific salt, the 'M' would represent a cation. Common examples include sodium metabisulfite (Na2S2O5) and potassium metabisulfite (K2S2O5).

The pyrosulfite ion is formed by the dehydration of two sulfite ions (SO3^2-). In aqueous solution, pyrosulfites are in equilibrium with sulfites. The exact equilibrium position depends on factors such as pH and temperature. M2S2O5 compounds are typically white crystalline solids. They are soluble in water and react with acids to release sulfur dioxide gas.

Sodium metabisulfite is widely used as a food preservative, antioxidant, and disinfectant. It is often found in wine, dried fruits, and processed foods to prevent spoilage and browning. Potassium metabisulfite also finds similar applications. Due to the release of sulfur dioxide, which can cause allergic reactions in some individuals, products containing metabisulfites are usually labeled accordingly. In industrial settings, M2S2O5 compounds are employed in photography, textile processing, and as bleaching agents.