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Na₂S₂O₃·5H₂O

Sodium thiosulfate pentahydrate

IUPAC : Sodium thiosulfate pentahydrate
SaltLaboratoryPharmaceuticalIndustrial

Mild reducing agent and complexing agent, historically used as a fixer in silver-halide photography (dissolves unexposed AgBr). Medical antidote for cyanide and chlorine poisoning.

3D ball-and-stick representation of Sodium thiosulfate pentahydrate (formula Na₂S₂O₃·5H₂O). Constituent atoms: Na, S, O.
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Physical properties

Molar mass248.18 g/mol
State at 20 °Csolid
Density1.667 g/cm³
Melting point321.65 K (48.50 °C)
Boiling point—
Solubility (H₂O)76.4 g/100 mL à 20 °C (forme pentahydrate)

Structure

Crystal systemMonoclinic
3D render modeBall-and-stick

Uses and applications

  • Silver-halide photography fixer (dissolves AgBr)
  • Cyanide poisoning antidote (emergency medicine)
  • Water treatment (neutralisation of residual chlorine — antichlor)
  • Iodometry (titration of iodine in analytical chemistry)
  • Aquariums (neutralising tap-water chlorine)

Constituent elements

11Na
Sodium
16S
Sulfur
8O
Oxygen

References

PubChem CID24345
CAS7772-98-7
SMILES[Na+].[Na+].[O-]S(=O)(=O)[S-]
Sources : PubChem CID 24345 · CRC Handbook of Chemistry and Physics