H2SiO42

H2SiO4^2−, commonly called dihydrogen silicate or the silicate dianion, is the dianionic form of silicic acid. It arises by deprotonation of silicic acid (H4SiO4) in water and represents one of the stepwise species in the acid–base equilibria of silica in aqueous solution. In solution, silicic acid exists predominantly as H3SiO4− at moderately basic pH and as H2SiO4^2− at higher pH, with further deprotonation to other silicate species occurring under strongly alkaline conditions.

Structure and properties: The central silicon atom is tetrahedrally coordinated to four oxygen atoms. The negative charge of H2SiO4^2− is delocalized over the oxygen atoms, and the ion can engage in hydrogen bonding and metal coordination. Its speciation and stability are highly dependent on pH and ionic strength.

Formation and occurrence: H2SiO4^2− forms in aqueous environments where silicic acid is present and pH is sufficiently high to drive deprotonation. It is an important component of the broader silicate equilibria that control silica solubility in natural waters and soils. The dianion can participate in forming salts with metal cations, contributing to the chemistry of silicate minerals and hydrous silicate networks.

Relevance and applications: In geochemistry and environmental chemistry, H2SiO4^2− contributes to the distribution of silicon species, influencing silica transport, weathering, and nutrient dynamics in soils and groundwater. It is also a reference species for understanding silicate speciation in laboratory and industrial settings, where silicate chemistry underpins glass production, water treatment, and catalyst materials.

See also: silicic acid, silicate ions, metasilicate, orthosilicic acid.