Sodium thiosulfate

Sodium thiosulfate

Names
IUPAC name Sodium thiosulfate
Other names Sodium hyposulfite Hyposulphite of soda
Identifiers
CAS Number	7772-98-7 Y 10102-17-7 (pentahydrate) N
3D model (Jmol)	Interactive image
ChEBI	CHEBI:132112 N
ChEMBL	ChEMBL2096650 (pentahydrate) N
ChemSpider	22885 Y
ECHA InfoCard	100.028.970
E number	E539 (acidity regulators, ...)
PubChem	24477
RTECS number	XN6476000
UNII	L0IYT1O31N Y
InChI InChI=1S/2Na.H2O3S2/c;;1-5(2,3)4/h;;(H2,1,2,3,4)/q2*+1;/p-2 Y Key: AKHNMLFCWUSKQB-UHFFFAOYSA-L Y InChI=1/2Na.H2O3S2/c;;1-5(2,3)4/h;;(H2,1,2,3,4)/q2*+1;/p-2 Key: AKHNMLFCWUSKQB-NUQVWONBAM
SMILES [Na+].[Na+].[O-]S([O-])(=O)=S
Properties
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
Structure
Crystal structure	monoclinic
Hazards
Safety data sheet	External MSDS
R-phrases	R35
NFPA 704	0 1 0
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 YN ?)
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.