SODIUM THIOSULPHATE Pentahydrate

Technical grade

General uses:

• Photographic processing - photographic fixer
• Aquariums - dechlorinating tapwater - see further details below
• Gold extraction

Sodium thiosulphate is also used:

• As a component in hand warmers and other chemical heating pads that produce heat by exothermic crystallization of a supercooled solution.
• In Bleach
• In pH testing of bleach substances.

Universal indicator and any other liquid pH indicator are destroyed by bleach, rendering them useless for testing the pH. If one first adds sodium thiosulphate to such solutions, it will neutralize the color-removing effects of bleach and allow one to test the pH of bleach solutions with liquid indicators. The relevant reaction is akin to the iodine reaction: thiosulphate reduces the hypochlorite (active ingredient in bleach) and in so doing becomes oxidized to sulfate. The complete reaction is:

4 NaClO + Na₂S₂O₃ + 2 NaOH = 4 NaCl + 2 Na₂SO₄ + H₂O

• To dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tap water requires between 0.1 grams and 0.3 grams of pentahydrated (crystalline) sodium thiosulphate per 10 liters of water.
• To lower chlorine levels in swimming pools and spas following super chlorination.
• To remove iodine stains.
• In bacteriological water assessment.
• In leather tanning.
• To demonstrate the concept of reaction rate in chemistry classes. The thiosulphate ion can decompose into the sulphite ion and a colloidal suspension of sulfur, which is opaque. The equation for this acid-catalysed reaction is as follows:

S₂O₃₂(aq) = SO₃₂(aq) + S(s)

• To demonstrate the concept of supercooling in physics classes. Melted sodium thiosulfate is very easy to overcool to room temperature and when crystallization is forced, the sudden temperature jump to 48.3^oC can be experienced by touch.
• As part of patina recipes for copper alloys.
• Safety Data Sheet MSDS