Characteristic

 

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. 

Chemical formula:Na₂SO₃

Molar mass:126.043 g/mol

Appearance:White solid

Odor: Odorless

Density:2.633 g/cm³ (anhydrous);1.561 g/cm³ (heptahydrate)

Melting point: 33.4 °C (92.1 °F; 306.5 K) (dehydration of heptahydrate)

500 °C (anhydrous)

Boiling point: Decomposes

Solubility in water:27.0 g/100 mL water (20 °C)

Solubility: Soluble in glycerol;Insoluble in ammonia, chlorine

log P:−4

Acidity (pKa):~9 (heptahydrate)

Refractive index (nD):1.565

Crystal structure:Hexagonal (anhydrous);Monoclinic (heptahydrate)

 

Application

 

Sodium sulfite is used in the photography industry to protect developing solutions from oxidation, in the pulp and paper industry, in water treatment as an oxygen scavenger agent, as a desulfurizing and dechlorinating agent in the leather industry and as a bleaching agent in textile industry. It is used as a preservative to prevent dried fruit from discoloring. It finds application as a sulfonation and sulfomethylation agent in the chemical industry. It is involved in the production of sodium thiosulfate. Other applications include forth flotation ores, oil recovery and making dyes.