Sodium thiosulfate

Sodium thiosulfate

Names
IUPAC name Sodium thiosulfate
Systematic IUPAC name Sodium thiosulfate
Properties
Chemical formula	Na2S2O3
Molar mass	158.11 g/mol (anhydrous) 248.18 g/mol (pentahydrate)
Appearance	White crystalline solid
Density	1.667 g/cm3
Melting point	48.3 °C (118.9 °F; 321.4 K) (pentahydrate)
Boiling point	100 °C (pentahydrate) 320 °C (608 °F; 593 K) (decomposes)
Solubility in water	70.1 g/100 mL (20 °C) 231 g/100 mL (100 °C)
Hazards
Safety data sheet	MSDS
Flash point	Non-flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sodium thiosulfate is an inorganic compound with the chemical formula Na₂S₂O₃. The solid is an efflorescent.

Properties

Chemical

Sodium thiosulfate reacts with acids, releasing sulfur, and sulfur dioxide fumes:

Na₂S₂O₃ + 2 HCl → 2 NaCl + S + SO₂ + H₂O

When heated to 300 °C, sodium thiosulfate decomposes to sodium sulfate and sodium polysulfide:

4 Na₂S₂O₃ → 3 Na₂SO₄ + Na₂S₅

Physical

Sodium thiosulfate is an odorless white crystalline solid, soluble in water, but almost insoluble in alcohols.

Availability

Sodium thiosulfate is sometimes sold in pharmacies or pet stores.

Preparation

Sodium thiosulfate can be prepared by boiling an aqueous sodium hydroxide solution with elemental sulfur.

Sodium sulfite can also be used instead of sodium hydroxide.

Projects

• Iodine clock reaction
• Neutralize bleach
• Remove iodine stains
• Cyanide poisoning antidote
• Gold extraction
• Supercooling demonstration
• Redox titrations
• Bunte salts synthesis
• Thioglycolic acid synthesis

Handling

Safety

Sodium thiosulfate may cause irritation on contact.

Storage

In closed containers.

Disposal

Not always required, but bleach can be used.

References

Relevant Sciencemadness threads

• Sodium Thiosulfate synthesis or aquisition
• Sodium Thiosulfate