Sodium sulphite

Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na₂SO₃. A pale yellow, water-soluble solid, it is used commercially as an antioxidant and preservative. A heptahydrate is also known but it is less useful because of its greater susceptibility toward oxidation by air.

Sodium sulfite is primarily used in the pulp and paper industry.

As an oxygen scavenger agent, it is used to treat water being fed to steam boilers to avoid corrosion problems, in the photographic industry, it protects developer solutions from oxidation and (as hypo clear solution) to wash fixer (sodium thiosulfate) from film and photo-paper emulsions

As a reducing agent it is used in the textile industry as a bleaching, desulfurizing, and dechlorinating agent (e.g. in swimming pools). Its reducing properties are exploited in its use as a preservative to prevent dried fruit from discoloring, and for preserving meats.

It is used as a reagent in sulfonation and sulfomethylation agent. It is used in the production of sodium thiosulfate.