Characteristic

 

Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula Na₂S₂O₃.xH₂O. Typically it is available as the white or colorless pentahydrate, Na₂S₂O₃·5H₂O. The solid is an efflorescent (loses water readily) crystalline substance that dissolves well in water.

Chemical formula:Na₂S₂O₃

Molar mass:158.11 g/mol (anhydrous);248.18 g/mol (pentahydrate)

Appearance:White crystals

Odor:Odorless

Density :1.667 g/cm³

Melting point: 48.3 °C (118.9 °F; 321.4 K) (pentahydrate)

Boiling point: 100 °C (212 °F; 373 K) (pentahydrate, - 5H2O decomposition)

Solubility in water:70.1 g/100 mL (20 °C);231 g/100 mL (100 °C)

Solubility: negligible in alcohol

Refractive index (nD):1.489

Crystal structure:monoclinic

 

Application

 

Sodium thiosulfate pentahydrate is used as an analytical reagent in laboratories. It is used in photographic processing and in gold extraction. Its alkylated derivatives, S-alkylthiosulfonates, are known as Bunte salts. It is involved in the preparation of thioglycolic acid. Furthermore, it is used to dechlorinate tap water, for removing free bromine from solutions and to check the pH of bleach solutions with liquid indicators. Other uses include tanning of leather; as an active component in hand warmers and chemical heating pads and as an anionic surfactant to aid in the dispersion of pharmaceutical preparations.