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OTHER CHEMICALS > Sodium Thiosulphate

Sodium thiosulfate, also spelled sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3·5H2O, an efflorescent, monoclinic crystalline substance also ...

Formula: Na2S2O3, Molar mass: 158.11 g/mol, Density: 1.67 g/cm³, Melting point: 48.3 °C, Boiling point: 100 °C, IUPAC ID: Sodium thiosulfate, Soluble in: Water


  • It is used as an antidote to cyanide poisoning. Thiosulfate acts as a sulfur donor for the conversion of cyanide to thiocyanate (which can then be safely excreted in the urine), catalyzed by the enzyme rhodanase.
  • It has also been used as treatment of calciphylaxis in hemodialysis patients with end-stage renal disease.
  • It is used in the management of extravasations during chemotherapy. Sodium thiosulfate prevents alkylation and tissue destruction by providing a substrate for the alkylating agents that have invaded the subcutaneous tissues. The dose may be 2mL of 0.17M (a solution of 4mL 10% sodium thiosulfate and 6mL sterile water for injection). It may be instilled subcutaneously into multiple sites using a small gauge needle. There are limited data on this method with few recommendations.
  • in foot baths for prophylaxis of ringworm, and as a topical antifungal agent for tinea versicolor.
  • in measuring the volume of extracellular body fluid and the renal glomerular filtration rate.

Sodium thiosulfate is also used:

  •  As a component in hand warmers and other chemical heating pads that produce heat by exothermic crystallization of a supercooled solution.
  • In bleach
  • In pH testing of bleach substances. The universal indicator and any other liquid pH indicators are destroyed by bleach, rendering them useless for testing the pH. If one first adds sodium thiosulfate to such solutions, it will neutralize the color-removing effects of bleach and allow one to test the pH of bleach solutions with liquid indicators. The relevant reaction is akin to the iodine reaction: thiosulfate reduces the hypochlorite (active ingredient in bleach) and in so doing becomes oxidized to sulfate. The complete reaction is:
  • 4 NaClO + Na2S2O3 + 2 NaOH → 4 NaCl + 2 Na2SO4 + H2O
  • To dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tap water requires between 0.1 grams and 0.3 grams of pentahydrated (crystalline) sodium thiosulfate per 10 liters of water.
  • To lower chlorine levels in swimming pools and spas following super chlorination.
  • To remove iodine stains, e.g. after the explosion of nitrogen triiodide.
  • Similarly, sodium thiosulfate reacts with bromine to render harmless products. Solutions of sodium thiosulfate are commonly used as a precaution in chemistry laboratories when working with bromine and for the safe disposal of bromine, iodine or other strong oxidizers.
  • In bacteriological water assessment, as it promotes the survival of coliform organisms by neutralizing residual chlorine.
  • In the tanning of leather.
  • To demonstrate the concept of reaction rate in chemistry classes. The thiosulfate ion can decompose into the sulfite ion and a colloidal suspension of sulfur, which is opaque. The equation for this acid-catalysed reaction is as follows:
  • S2O32−(aq) → SO32−(aq) + S(s)
  • To demonstrate the concept of supercooling in physics classes. Melted sodium thiosulfate is very easy to overcool to room temperature and when crystallization is forced, the sudden temperature jump to 48.3 °C can be experienced by touch.
  • As part of patina recipes for copper alloys.
  • Often used in pharmaceutical preparations as an anionic surfactant to aid in dispersion.
  • It can also be used as a very interesting solute in supersaturation experiments.
  • As an ingredient to table salt, e.g. Sysco Corporation's small packets of Iodized Salt.