CAS number 7772-98-7 identifies sodium thiosulfate. This chemical substance is widely known and utilized across various industries and applications due to its versatile properties.
Understanding Sodium Thiosulfate
Sodium thiosulfate (chemical formula: Na₂S₂O₃) is an inorganic salt often encountered as its pentahydrate form (Na₂S₂O₃·5H₂O), a white crystalline solid. A CAS (Chemical Abstracts Service) Registry Number, such as 7772-98-7, is a unique numerical identifier assigned to every chemical substance described in the scientific literature, ensuring a definitive and unambiguous way to identify chemicals.
Key Properties
Sodium thiosulfate is characterized by several important properties that contribute to its diverse uses:
| Property | Description |
|---|---|
| Chemical Formula | Na₂S₂O₃ |
| Molar Mass | 158.11 g/mol (anhydrous) / 248.18 g/mol (pentahydrate) |
| Appearance | White crystalline solid |
| Solubility | Highly soluble in water, insoluble in alcohol |
| Odor | Odorless |
| Reactivity | Reducing agent, reacts with acids to produce sulfur dioxide and sulfur |
Primary Applications and Uses
Sodium thiosulfate's reactivity, particularly its reducing properties and ability to complex with metal ions, makes it invaluable in numerous fields:
- Photography: Perhaps its most famous historical use is as a "fixing agent" or "hypo" in photographic processing. It dissolves unexposed silver halide salts from photographic films and papers, making the image permanent and resistant to light.
- Medical Applications:
- Antidote for Cyanide Poisoning: Administered intravenously, it acts as a sulfur donor for the enzyme rhodanese, converting highly toxic cyanide into much less toxic thiocyanate.
- Chemotherapy Extravasation: Used to neutralize the effects of certain chemotherapy drugs (e.g., cisplatin) if they leak out of the vein into surrounding tissues.
- Topical Antifungal Agent: Sometimes used topically for skin conditions like tinea versicolor.
- Water Treatment: It is an effective dechlorinating agent, commonly used to remove chlorine from tap water for various purposes, including aquariums, swimming pools, and in laboratory settings to stop oxidation reactions.
- Analytical Chemistry: Employed in iodometric titrations as a reducing agent to determine the concentration of oxidizing agents.
- Industrial Uses:
- Gold Extraction: Can be used as a non-toxic alternative to cyanide for leaching gold and silver from their ores.
- Textile Industry: Used as an antichlore to remove excess chlorine after bleaching processes.
- Leather Tanning: Applied in certain steps of the leather processing.
Safety and Handling
While generally considered safe for its intended uses, sodium thiosulfate should be handled with care. Ingestion of large quantities can cause gastrointestinal upset. When heated, it decomposes to release toxic sulfur oxides. Always follow proper laboratory and industrial safety protocols, including wearing appropriate personal protective equipment, when working with this substance.
