Chemical properties

Hydrogen peroxide is inherently unstable: its aqueous solution spontaneously disproportionates into water and oxygen. Left alone, this decomposition is slow, but it becomes explosively fast when catalysed by traces of metal:

If H₂O₂ is stored in an ordinary glass container, it slowly dissolves alkali-metal ions out of the glass, and these dissolved metal ions catalyse exactly this disproportionation reaction -- which is why H₂O₂ solutions are, in practice, always stored in plastic bottles instead.

Hydrogen peroxide as an oxidising agent. H₂O₂ can act as an oxidising agent, typically in acidic medium:

For example, it oxidises Fe²⁺ to Fe³⁺:

Hydrogen peroxide as a reducing agent. In basic medium, H₂O₂ instead acts as a reducing agent:

For example, it reduces potassium permanganate:

$2\,KMnO_4(aq) + 3\,H_2O_2(aq) \rightarrow 2\,MnO_2 + 2\,KOH + 2\,H_2O + 3\,O_2(g)$ …