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Chemistry LibreTexts

Hydrogen Peroxide

Hydrogen peroxide (H2O2) is a viscous liquid (mp.: -0.89°C, bp.: 152.1°C, density: 1.448 g/cm3 at 20°C) that has strong oxidizing properties.

It is commonly used (in concentrations typically around 5%) to bleach human hair, hence the phrases "peroxide blonde" and "bottle blonde". It burns the skin upon contact in sufficient concentration. In lower concentrations (3%), it is used medically for cleaning wounds and removing dead tissue. However, recent studies have indicated that hydrogen peroxide is toxic to new cells and is therefore not recommended for wound care. The same solution is often used by medical professionals to clean blood from cloth and equipment.

H2O2 is produced by a combination of electrolysis of sulfuric acid and subsequent hydrolysis of the resulting peroxo-disulfuric acid:

2 H2SO4 H2S2O8 + H2
H2S2O8 + 2 H2O H2O2 2 H2SO4

2 H2O H2O2 + H2

Hydrogen peroxide decomposes exothermically into water and oxygen gas (46.87 kcal/mol). However, at room temperature the rate of decomposition is very low, so that pure H2O2 is stable (metastable). Catalysts (like pulverized silver, gold, platinum, manganese dioxed, iron and copper salts, alkali salts, dust, activated carbon, etc.) dramatically increase the rate of decomposition. High concentrations of H2O2 may lead to explosions when it comes into contact with catalysts. H2O2 may be stabilized by adding phosphoric acid, sodium diphosphate, uric acid, or barbituric acid. Pure H2O2 without any stabilizers can only be stored in glass bottles which are coated with paraffin way, or in pure aluminum (better than 99.9 %) bottles.