Sodium thiosulfate
| Names | |
|---|---|
| IUPAC name
Sodium thiosulfate
| |
| Systematic IUPAC name
Sodium thiosulfate | |
| Other names
Sodium thiosulphate
Sodium hyposulfite Hyposulphite of soda | |
| Properties | |
| Na2S2O3 | |
| Molar mass | 158.11 g/mol (anhydrous) 248.18 g/mol (pentahydrate) |
| Appearance | White crystalline solid |
| Odor | Odorless |
| Density | 1.667 g/cm3 |
| Melting point | 48.3 °C (118.9 °F; 321.4 K) (pentahydrate) |
| Boiling point | 100 °C (pentahydrate) 320 °C (608 °F; 593 K) (decomposes) |
| 70.1 g/100 mL (20 °C) 231 g/100 mL (100 °C) | |
| Solubility | Almost insoluble in ethanol, methanol |
| Vapor pressure | ~ 0 mmHg |
| Hazards | |
| Safety data sheet | MSDS |
| Flash point | Non-flammable |
| Related compounds | |
| Related compounds
|
Sodium metabisulfite Sodium sulfite |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| Infobox references | |
Sodium thiosulfate is an inorganic compound with the chemical formula Na2S2O3, widely used in titrations and as cyanide poisoning antidote. The most common form of this salt is the pentahydrate Na2S2O3·5H2O. This solid is slightly efflorescent.
Contents
Properties
Chemical
Sodium thiosulfate reacts with acids, releasing sulfur, and sulfur dioxide fumes:
- Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O
The hydrated form has a low melting point of around 50 °C, but in fact it decomposes and the salt dissolves in its own water of crystallization. When heated more strongly, the water is driven off. When the anhydrous compound is heated to 300 °C, it decomposes to sodium sulfate and sodium polysulfide:
- 4 Na2S2O3 → 3 Na2SO4 + Na2S5
Physical
Sodium thiosulfate pentahydrate is an odorless white crystalline solid, soluble in water, but almost insoluble in alcohols.
Availability
Sodium thiosulfate is sometimes sold in pharmacies or pet stores. It can be bought cheaply online.
Preparation
Sodium thiosulfate can be prepared by boiling an aqueous sodium hydroxide solution with elemental sulfur, but isolation of the pure solid is not easy. The other reaction product is sulfide and polysulfide.
Sodium sulfite can also be used instead of sodium hydroxide. In that case, the only reaction product is sodium thiosulfate.
Projects
- Iodine clock reaction
- Neutralize bleach
- Remove iodine stains
- Cyanide poisoning antidote
- Gold extraction
- Supercooling demonstration
- Redox titrations
- Bunte salts synthesis
- Thioglycolic acid synthesis
Handling
Safety
Sodium thiosulfate may cause irritation on contact.
Storage
Sodium thiosulfate should be kept in closed containers.
Disposal
No special precautions need to be taken. Bleach can be used to neutralize it to sulfate.
