Sodium pyrosulphite

Chemical formula Na2S2O5

White, compact grained powder with a weak odour of sulphur dioxide(SO2). Aqueous solutions show a slightly acid reaction. If moisture acts on it, it gradually seperates gaseous sulphur dioxide resulting in oxidation to sodium sulphate. If acids and heat act on it, sulphur dioxide will evolve. Sodium pyrosulphite is easy soluble in water forming sodium hydrogen sulphite.

Sodium metabisulphite is used in various applications. Some examples of applications are listed below.

Sodium metabisulphite:
• reacts heavily with oxidants 
• has a bleaching reducing and preserving effect