What is Sodium Thiosulfate? - Formula & Properties

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson goes over a boring-sounding compound called sodium thiosulfate. But what's really cool is that this compound can be used to treat deadly cyanide poisoning. Find out how.

Sodium Thiosulfate

One of the deadliest poisons known to mankind is cyanide. Cyanide poisoning can lead to a fast heart rate and rapid breathing. A person can have a seizure, lose consciousness and eventually die as a result.

Yet there are treatments for people who can get to a hospital fast enough. One of these treatments involves a chemical medication known as sodium thiosulfate. This lesson describes its formula and properties.


Sodium thiosulfate has a molecular formula of Na2 O3 S2. Here the Na stands for sodium, the O stands for oxygen, and the S stands for sulfur. You can probably spot the sodium and sulfate in the name, sodium thiosulfate. The oxygen is also part of the sulfate, since a sulfate is a sulfur atom bonded to oxygen atoms.


At room temperature, sodium thiosulfate is found in powdered or colorloess crystal form. Here are some basic facts about this compound:

  • molecular weight = 158.097 g/mol
  • exact mass = 157.908 g/mol
  • melting point = 48.5 degrees Celsius (119.3 degrees Fahrenheit)
  • density =1.7 g/cm3

When heated, sodium thiosulfate can produce very toxic fumes of disodium oxide and sulfur oxides. Sodium thiosulfate can also donate its sulfur atoms, if need be.

And that latter property is key to tying back to our introduction since you're probably most interested in finding out how this chemical can be used in medicine to save the life of a victim of cyanide poisoning.

Converting Cyanide

Believe it or not, your body has a system to detoxify itself of cyanide. This system depends on an enzyme called rhodanese, which converts cyanide (CN-) into thiocyanate (SCN-). Thiocyanate is basically the less toxic version of cyanide.

Of course, if a person takes too much cyanide, this life-saving system becomes overloaded and rhodanese cannot transform cyanide into thiocyanate fast enough to save your life.

Sodium thiosulfate to the rescue! You can think of sodium thiosulfate as a charity. Instead of giving away food or clothing, it donates its sulfur atoms. By giving away a sulfur (S) atom, it allows rhodanese to transform cyanide into thiocyanate more quickly. Remember, CN- becomes SCN-. Note the sulfur atom in the thiocyanate (SCN-), which renders the original cyanide far less harmful.

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