Hydrogen Peroxide : Hydrogen Peroxide, Stability

Solutions of hydrogen peroxide readily decompose spontaneously into water and oxygen in presence of traces of alkali. They become much more stable in presence of traces of sulphuric or phosphoric acids; the commercial peroxide, but not Merck's perhydrol, is acid. The addition of alcohol, glycerin, or barbituric acid also renders the solutions stable. The vapour appears to be stable.

Hydrogen peroxide closely resembles ozone in many respects. Although it is an exothermic compound when formed from the elements: H₂ + O₂ = H₂O₂ + 45.2 k. cal., hydrogen peroxide readily decomposes into gaseous oxygen and water, and is unstable at the ordinary temperature. As in the case of ozone, one of the oxygen atoms tends to split off, with the formation of gaseous oxygen and water and this decomposition is attended with a very large evolution of heat: 2H₂O₂ = 2H₂O + O₂ + 2 x 23.0 k. cal.

Hydrogen peroxide is produced in some combustion reactions. If a hydrogen or carbon monoxide flame is allowed to impinge on the surface of cold water, ice, or solid carbon dioxide, hydrogen peroxide is found in the liquid.

Traces of hydrogen peroxide are formed by passing a mixture of hydrogen and oxygen over palladium-black: H₂ + O₂ = H₂O₂. Small amounts are also formed by the action of bright sunlight, ultra-violet light, or radium emanation on water containing dissolved oxygen; or by the action of a brush discharge on a mixture of steam and oxygen, 2H₂O + O₂ = 2H₂O₂, or on a non-explosive mixture of hydrogen and oxygen at -80°, or the mixture H₂ + O₂ at 3 cm. pressure. It is not produced by the spontaneous evaporation of water in air unless traces of zinc are present, although snow is said to contain it in traces. Minute quantities of hydrogen peroxide are said to be formed in plants.

Expt. 3. - Allow a hydrogen flame to impinge on a piece of ice. Pour out the liquid produced, and add a little titanic acid solution: a yellow colour indicates the presence of hydrogen peroxide.

Protein crystallography
Chemistry guide
Hydrogen Peroxide
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