SO42ioniin

SO42ioniin, commonly known as the sulfate ion, is the chemical species with formula SO4^2−. It is a tetrahedral oxoan anion of sulfur in oxidation state +6. In the sulfate ion, the four oxygen atoms are equivalent by resonance, yielding four S–O bonds of essentially equal character. The overall charge is −2, and the ion is typically encountered in aqueous solutions as a stable constituent of many salts.

In water, sulfate is the conjugate base of sulfuric acid; the second dissociation has a pKa around 1.99, so at moderate pH the predominant species is SO4^2−. It forms soluble salts with many cations, such as sodium sulfate and potassium sulfate, and it can participate in interactions with metals and with mineral surfaces in soils and sediments.

Occurrence and applications: SO4^2− occurs widely in nature in minerals such as gypsum (CaSO4·2H2O) and anhydrite (CaSO4). It is abundant in seawater and groundwater. Sulfate is produced by the oxidation of sulfide minerals and by combustion processes that release sulfur oxides, which oxidize to sulfate in the atmosphere and deposition systems. Industrially, sulfate salts are used in fertilizers (for example ammonium sulfate), glassmaking, papermaking, detergents, and various chemical processes. Environmental considerations include the role of sulfate in acid rain and in the formation of atmospheric aerosols; elevated sulfate concentrations in water can affect taste and may have laxative effects.

Safety and handling: sulfate itself has relatively low acute toxicity, but very high levels can cause digestive discomfort and osmotic effects in exposed organisms.