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Sodium thiosulfate

Sodium thiosulfate
Sodium thiosulfate
Crystal structure of sodium thiosulfate pentahydrate
Sodium thiosulfate.jpg
Names
IUPAC name
Sodium thiosulfate
Other names
Sodium hyposulfite
Hyposulphite of soda
Identifiers
7772-98-7 YesY
10102-17-7 (pentahydrate) N
3D model (Jmol) Interactive image
ChEBI CHEBI:132112 N
ChEMBL ChEMBL2096650 (pentahydrate) N
ChemSpider 22885 YesY
ECHA InfoCard 100.028.970
E number E539 (acidity regulators, ...)
PubChem 24477
RTECS number XN6476000
UNII L0IYT1O31N YesY
Properties
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)
70.1 g/100 mL (20 °C)
231 g/100 mL (100 °C)
Solubility negligible in alcohol
1.489
Structure
monoclinic
Hazards
Safety data sheet External MSDS
R-phrases R35
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Sodium thiosulfate (Na2S2O3), also spelled sodium thiosulphate, is a chemical and medication. As a medication it is used to treat cyanide poisoning and pityriasis versicolor.

It is an inorganic compound that is typically available as the pentahydrate, Na2S2O3·5H2O. The solid is an efflorescent (loses water readily) crystalline substance that dissolves well in water. It is also called sodium hyposulfite or “hypo”.

It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.

In analytical chemistry, the most important use comes because the thiosulfate anion reacts stoichiometrically with iodine in aqueous solution, reducing it to iodide as it is oxidized to tetrathionate:

Due to the quantitative nature of this reaction, as well as because Na2S2O3·5H2O has an excellent shelf-life, it is used as a titrant in iodometry. Na2S2O3·5H2O is also a component of iodine clock experiments.

This particular use can be set up to measure the oxygen content of water through a long series of reactions in the Winkler test for dissolved oxygen. It is also used in estimating volumetrically the concentrations of certain compounds in solution (hydrogen peroxide, for instance) and in estimating the chlorine content in commercial bleaching powder and water.


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