Натрия тиосульфа

Химические свойства

Sodium thiosulfate, Na2S203·5H20, also known as sodium hyposulfite, hypo,andsodium subsulfite, is a white crystalline solid that has a melting point of 48 °C(118 °F). Water soluble,it is used as a fixing agent for photographic films, plates, and papers. Sodium thiosulfate is used in medicine, as a germicide, in manufacturing leather, as a mordant in dyeing, and for extracting silver from ore.

Физические свойства

Anhydrous thiosulfate is a white powder; soluble in water; insoluble in ethanol.
Sodium pentahydrate is a colorless, odorless, crystalline solid; density 1.69 g/cm³; decomposes around 50°C; effloresces in dry air above 33°C; very soluble in water and oil of turpentine; insoluble in ethanol.

Использование

Sodium thiosulfate is a common analytical reagent used in iodometric titration to analyze chlorine, bromine, and sulfide. Other uses are in bleaching paper pulp, bleaching straw, ivory, and bones, for removing chlorine from solutions, silver extraction from its ores, a mordant in dyeing and printing textiles, and as an antidote to cyanide poisoning.
Another major application is in photography, where it is used as a fixer to dissolve unchanged silver salts from exposed negatives.
Sodium Thiosulfate is used primarily as a medicament against cyanide poisoning, able to convert cyanide into thiocyanate, a reaction which is catalyzed by the enzyme Rhodanese. Antioxidant.

Определение

ChEBI: An inorganic sodium salt composed of sodium and thiosulfate ions in a 2:1 ratio.

Подготовка

Sodium thiosulfate is a common reducing agent. It reduces iodine to iodide anion forming sodium tetrathionate. This reaction is utilized in the so-called iodometric titration: 2S₂O₃²ˉ + I₂ → S₄O₆²ˉ + 2Iˉ
Sodium thiosulfate reacts with chlorine to form sodium bisulfate and hydrochloric acid. This reaction removes chlorine from aqueous solutions:Na₂S₂O₃ + 4Cl₂ + 5H₂O → 2NaHSO₄ + 8HCl
Sodium thiosulfate reacts with hydrochloric acid, decomposing to sulfur and sulfur dioxide: Na₂S₂O₃ + 2HCl → 2NaCl + S + SO₂ + H₂O.

Общее описание

Sodium thiosulfate (Na₂S₂O₃) can be obtained from Na₂S₂O₃.10H₂O by heating above 100 °C. It can be synthesized from sodium sulfate.

Опасность

Use in foods restricted to 0.1%.

Профиль безопасности

Moderately toxic by subcutaneous route. Incompatible with metal nitrates, sodium nitrite. When heated to decomposition it emits very toxic fumes of Na2O and SOx. See also SODIUM THIOSULFATE and SODIUM THIOSULFATE, PENTAHYDRATE.

Методы очистки

Crystallise it from EtOH/H2O solutions or from water (0.3mL/g) below 60o by cooling to 0o, and dry it at 35o over P2O5 under vacuum. [Foerster & Mommsen Chem Ber 57 258 1924.] This salt is used as a secondary standard in volumetric analysis [Kilpatrick J Am Chem Soc 45 2132 1923], and is used as “Hypo” in photography [Hargreaves & Dunningham J Soc Chem Ind 42 147T 1923.]