Sodium thiosulfate

 

Sodium thiosulfate

Chemical formula	Na2S2O3
OTP appearance	white crystals
Molar Mass(g/mol)	158.11
Density(g/cc)	1.667
Melting Point(°C)	48.3
Boiling Point(°C)	100
Solubility in water(g/L)	701
Solubility in ethanol(g/L)	non
NFPA 704	0 1 0

Uses

Primary

• Pharm: WHO LEM cyanide antidote (also hydroxocobalamin) Can be delivered by IM injection in the treatment of cyanide poisoning.

Secondary

• Iodometry (2 Na₂S₂O₃ + I₂ → Na₂S₄O₆ + 2 NaI // Converts elemental iodine to ionic iodine, clearing the solution)
• Neutralization of halide compounds
• Cooling slurry with water

Production

Synthesis

Direct

1. Boil a solution of sodium hydroxide with sulfur in the correct stochiometric ration, producing (less soluble, 180g/L) sodium sulfide and (very soluble, 701g/L) sodium thiosulfate.

   6 NaOH(aq) + 4 S

   {

   →

   100°C}

   2 Na₂S + Na₂S₂O₃ + 3 H₂O

2. The sulfide biproduct can be converted to thiosulfate as well by combination with sulfur dioxide, recovering some of the initial sulfur.

   2 Na₂S + 3 SO₂ → 2 Na₂S₂O₃ + S

via sodium sulfite

Add sulfur to a solution of sodium sulfite

Na₂SO₃ + S → Na₂S₂O₃