Sodium thiosulfate is an inorganic compound with a chemical formula Na2S2O3. It is also known as Disodium thiosulfate or Sodium hyposulfite or Hyposulphite of soda. The molecular weight of disodium thiosulfate is 158.11 g/mol.
Physical and Chemical properties of Sodium thiosulfate
It is a white crystalline with no odour. The density of Sodium hyposulfite is 1.667 g/cm3, and the refractive index is approximately 1.489. Its boiling point is 48.3 °C and has a melting point of 100 °C.
Production of Sodium thiosulfate
At an industrial level, sodium thiosulfate is produced mainly from liquid waste products of sulfur dye or sodium sulfide.
At a laboratory level, sodium thiosulfate is prepared by either
- Heating aqueous solution of sodium sulfite in the presence of sulfur or
- Boiling aqueous sulfur or sodium hydroxide. The equation is as follows:
6 NaOH + 4 S → 2 Na2S + Na2S2O3 + 3 H2O
Uses of Sodium thiosulfate:
- Medical use – It is used in the treatment of cyanide poisoning, ringworm and tinea versicolor. Also, it is used in the treatment of some side effects of chemotherapy and hemodialysis.
- Photographic processing – It is used for photographic paper processing.
- Extraction of gold – Ammonium thiosulfate and sodium thiosulfate are a component of an alternative lixiviant to cyanide to extract gold.
- Iodometry – In analytical chemistry, thiosulfate anion reacts with iodine stoichiometrically in aqueous solution, which reduces to iodide and the thiosulfate oxidized to tetrathionate. The reaction is as follows:
2 S2O2−3 + I2 → S4O2−6 + 2 I−
Reactions of Sodium thiosulfate
- When sodium thiosulfate is heated to 300 °C, it decomposes to sodium polysulfide and sodium sulfate. The reaction is as follows:
4 Na2S2O3 → 3 Na2SO4 + Na2S5
- Acidification of this salt with even dilute acids gives incomplete decomposition to sulfur dioxide, water, and sulfur. The reaction is given below:
Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O
- Alkylation of sodium thiosulfate produces S-alkyl thiosulfates. The reaction is explained by the synthesis of thioglycolic acid.
ClCH2CO2H + Na2S2O3 → Na[O3S2CH2CO2H] + NaCl
Na[O3S2CH2CO2H] + H2O → HSCH2CO2H + NaHSO4
- Aluminium cation reaction –
When sodium thiosulfate is heated with a sample that contains aluminium cations, it produces a white precipitate. The reaction is given below:
2 Al3+ + 3 S2O2−3 + 3 H2O → 3 SO2 + 3 S + 2 Al(OH)3
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