Sodium thiosulfate pentahydrate is an inorganic compound with the chemical formula Na₂S₂O₃·5H₂O. It's a hydrate of sodium thiosulfate, meaning it contains five water molecules per molecule of sodium thiosulfate. It appears as white or colorless crystals and is commonly used as a photographic fixing agent, in water treatment to remove chlorine, and as an antidote for cyanide poisoning. Common Uses: Photography: Used as a photographic fixing agent to dissolve unexposed silver halide crystals. Water Treatment: Neutralizes and removes chlorine and chloramines from water. Medical: Used as an antidote for cyanide poisoning and to reduce the risk of ototoxicity associated with cisplatin treatment in pediatric cancer patients according to the National Cancer Institute. Other: Also used in leather tanning, paper manufacturing, and as a laboratory reagent.