Sodium thiosulfate

Sodium Thiosulfate (also known as sodium hyposulfite or "hypo") is an inorganic compound represented by the formula Na2S2O3. It is a colorless, crystalline solid that is more commonly encountered as a pentahydrate, Na2S2O3•5H2O. Sodium thiosulfate has a wide range of uses in various industries, including photography, medicine, and water treatment.

Chemical Properties

Sodium thiosulfate is an ionic compound made up of two sodium ions (Na+) and one thiosulfate ion (S2O3-). The thiosulfate ion is a polyatomic ion in which two sulfur atoms are bonded to three oxygen atoms. One of the sulfur atoms has an oxidation state of +6 and the other has an oxidation state of +2. The overall charge of the ion is -2.

Production

Sodium thiosulfate is produced industrially by the reaction of sodium sulfite with sulfur. Alternatively, it can be produced by boiling sodium sulfide with sulfur.

Uses

Photography

In photography, sodium thiosulfate is used as a fixing agent to dissolve unaltered silver salts from exposed photographic film or photographic paper.

Medicine

In medicine, sodium thiosulfate is used as an antidote to cyanide poisoning. It works by converting the poisonous cyanide into thiocyanate, a compound that is less toxic and can be excreted in urine.

Water Treatment

In water treatment, sodium thiosulfate is used to dechlorinate tap water including lowering chlorine levels for use in aquariums.

Safety

Sodium thiosulfate is generally considered safe for handling. However, exposure to large amounts can cause irritation to the eyes, skin, and respiratory tract.

See Also

• Sodium sulfite
• Sodium sulfide
• Cyanide poisoning