Hydrogen peroxide is one of the hydrides formed by the combination of hydrogen with oxygen. The other hydride is water. Hydrogen peroxide was first prepared by Thenard by the action of dilute tetraoxosulphate(VI) acid on barium peroxide. He found out that hydrogen peroxide, H2O2 contained more oxygen molecule than water, H2O and this discovery prompted him to call it oxygenated water.
Hydrogen peroxide occurs in trace amounts in nature. It occurs in dews and in air. It also occurs in water that has been exposed to brilliant sunshine.
Laboratory Preparation of Hydrogen Peroxide: Hydrogen peroxide is prepared in the laboratory by the action of dilute acid on some metallic peroxides. A salt is also produced as bi-product of the reaction. Most often, barium peroxide is used alongside with dilute tetraoxosulphate(IV) acid. The reason for this is that the barium tetraoxosulphate(VI) produced is insoluble and can readily be filtered off the system.
H2SO4(aq) + BaO2(s) → BaSO4(s) + H2O2(aq)
Industrial Preparation of Hydrogen Peroxide: Hydrogen peroxide is produced industrially by the oxidation of propan-2-ol with oxygen. The reaction is carried out under slight pressure.
It can also be produced industrially by the oxidation of substituted anthracene-9, 10-diones. The solution of hydrogen peroxide obtained can be concentrated by distilling it under reduced pressure. Since hydrogen peroxide is easily decomposed by light, it is stored in dark glass containers or bottles or in aluminium containers. Moreover, a solution of hydrogen peroxide must be kept pure to prevent its catalytic decomposition.
Hydrogen peroxide is sold in various concentrations and these concentrations are expressed as its volume-strength which is the number of volumes of oxygen(measured at s.t.p), that is liberated by one volume of hydrogen peroxide on heating. This means that 1cm3 of a 10-volume solution of hydrogen peroxide would liberate 10cm3 of oxygen(at s.t.p) when it decomposes completely. Hydrogen peroxide are usually sold at concentration levels of 10-volume, 20-volume and 30-volume.
Uses of Hydrogen Peroxide
Some of the uses of hydrogen peroxide include:
(i) One of the most important uses of hydrogen peroxide in medicine is its use as an antiseptic.
(ii) Liquid hydrogen peroxide provides oxygen for the burning of fuel in space rockets. Hydrogen peroxide is also used in the burning of diesel oil in the engines of submerged submarines.
(iii) Hydrogen peroxide is used in bleaching delicate materials such as silk, wood pulp, wool, human hair and feathers. This use is particularly needed especially when chlorine or sulphur(IV) oxide could cause damage to the material when used for bleaching.
(iv) Hydrogen peroxide is used in the manufacture of chemical compounds such as sodium dioxochlorate(III) and some organic peroxides which are used in initiating polymerization reactions.
(v) Mixtures such as white lead(II) paints that contain lead(II) tetraoxocarbonate(IV) blackens when exposed to atmospheric hydrogen sulphide because the lead(II) compounds present are readily converted into lead(II) sulphide. Therefore treatment with hydrogen peroxide oxidizes the lead(II) sulphide to lead(II) tetraoxosulphate(VI), thereby restoring the original white color.
PbS(s) + 4H2O2(aq) → PbSO4 + 4H2O(l)