Thiosulfate ion (S₂O₃²⁻)
- Charge
- −2
- Atoms
- S × 2, O × 3
- Atoms in total
- 5
- Mass of the ion
- 112.117 g/mol
Thiosulfate is a sulfate ion in which one oxygen atom has been replaced by a sulfur atom, so it has two sulfur atoms and three oxygen atoms. Because sulfur simply takes the place of an oxygen, the charge stays at 2−. You meet it as the “hypo” that fixes black-and-white photographs, as a treatment for cyanide poisoning and in lab titrations with iodine.
- Thio- means a sulfur atom has replaced an oxygen atom, the same prefix used in thiocyanate, SCN⁻.
- In acid, thiosulfate breaks down to solid sulfur that slowly clouds the solution, a reaction used in school rate-of-reaction experiments.
- Sodium thiosulfate, Na₂S₂O₃, is also used to remove chlorine from aquarium water.