Hydrogen peroxide was first prepared by L.J.Thenard, in 1813 by the action of dilute acid on barium peroxide. Traces of H2O2 are found in atmosphere and in certain plants.
Laboratory preparation of hydrogen peroxide
1. By the action of dilute sulphuric acid on sodium peroxide. Calculated quantity of Na2O2 is added in small proportions to a 20% ice cold solution of sulphuric acid.
Na2O2 + H2SO4 --- > Na2 SO4 + H2O2
30% solution of H2O2 is obtained by this process.
2. Pure H2O2 is obtained by reacting BaO2 with an acid BaO2 + H2SO4 -- > Ba SO4 + H2O2
3BaO2 + 2H3 PO4 -- > Ba3 (PO4)2 + 3H2O2
3. H2O2 is manufactured by followed by vacuum distillation. H2O2.
H2SO4 -- > < --- H+ + HSO4-
2HSO4- -- > < --- H2S2O8 + 2e- (At anode)
H2S2O8 + H2O -- > < --- H2SO4 + H2SO5
H2SO5 + H2O -- > < --- H2SO4 + H2O2
2H+ + 2e- -- > < --- H2 (At cathode)
Concentration of hydrogenperoxide solution
The impurities like organic material or metallic ions, may catalyse its explosive decomposition.
1. By careful evaporation of the solution obtained above on a water bath preferably under reduced pressure using fractionating column.
2. By distillation under reduced pressure at temperatures below 330K, the concentration up to 90% solution is used till crystallisation formed.
Strength of Hydrogenperoxide
The strength of a sample of hydrogen peroxide solution is expressed in terms of the volumes of oxygen at S.T.P that one volume of H2O2 gives on heating.
H2O2 is a colourless, odourless, syrupy liquid in the anhydrous state. It is miscible with water, alcohol, and ether in all proportions.
Pure H2O2 is unstable and decomposes on standing. On heating when water and oxygen are formed.
2H2O2 -- > 2H2O + O2
H2O2 is a powerful oxidizing agent. It functions as an electron acceptor. H2O2 + 2H+ + 2e- -- > 2 H2O
(In acidic solution)
H2O2- + 2e- -- > 2OH-
(In alkaline solution)
It oxidises PbS to PbSO4
PbS+ 4H2O2 -- > PbSO4 +4H2O
It oxidizes ferrous salts int2Fe2+ + 2H+ + H2O2 --> 2 Fe3+ + 2H2O
Due to its oxidizing property, it is a valuable bleaching agent, powerful but harmless disinfectant and germicide. Delicate materials like silk, wool, hair which will be destroyed by chlorine, are bleached with H2O2.
With powerful oxidizing agents, H2O2 acts as a reducing agent. Moist silver oxide, acidified KMnO4, ozone, chlorine and alkaline solutions of ferricyanides are reduced.
Ag2O + H2O2 --> 2 Ag + H2O + O2
1. It destroys bacteria and hence it is used as an antiseptic and germicide for washing wounds, teeth and ears.
2. It destroys the colour of some organic compounds and is used in bleaching delicate things like hair, wool, silk ivory and feathers.
3. It is used as an oxidizing agent.
4. It is also used as a propellant in rockets.o ferric salts .