9.7 Hydrogen Peroxide (H2O2)
NEETprep Audio Note:
9.7.1 Preparation
It can be prepared by the following methods.
(i) Acidifying barium peroxide and removing excess water by evaporation under reduced pressure gives hydrogen peroxide.
(ii) Peroxodisulphate, obtained by electrolytic oxidation of acidified sulphate solutions at high current density, on hydrolysis yields hydrogen peroxide.
This method is now used for the laboratory preparation of D2O2.
(iii) Industrially it is prepared by the auto-oxidation of 2-alklylanthraquinols.
In this case 1% H2O2 is formed. It is extracted with water and concentrated to ~30% (by mass) by distillation under reduced pressure. It can be further concentrated to ~85% by careful distillation under low pressure. The remaining water can be frozen out to obtain pure H2O2.
9.7.2 Physical Properties
NEETprep Audio Note:
H2O2 is miscible with water in all proportions and forms a hydrate H2O2.H2O (mp 221K). A 30% solution of H2O2 is marketed as ‘100 volume’ hydrogen peroxide. It means that one millilitre of 30% H2O2 solution will give 100 mL of oxygen at STP. Commercially marketed sample is 10 V, which means that the sample contains 3% H2O2.
Problem 9.4
Calculate the strength of 10 volume solution of hydrogen peroxide. NEETprep Audio Note:
Solution
10 volume solution of H2O2 means that 1L of this H2O2 solution will give 10 L of oxygen at STP
2×34 g 22.7 L at STP
68 g
On the basis of above equation 22.7 L of O2 is produced from 68 g H2O2 at STP
10 L of O2 at STP is produced from 
Therefore, strength of H2O2 in 10 volume H2O2 solution = 30 g/L = 3% H2O2 solution
9.7.3 Structure
NEETprep Audio Note:
Fig. 9.3 (a) H2O2 structure in gas phase, dihedral angle is 111.5°. (b) H2O2 structure in solid phase at 110K, dihedral angle is 90.2°.
9.7.4 Chemical Properties
NEETprep Audio Note:
(i) Oxidising action in acidic medium
(ii) Reducing action in acidic medium
(iii) Oxidising action in basic medium
(iv) Reducing action in basic medium
9.7.5 Storage
NEETprep Audio Note:
In the presence of metal surfaces or traces of alkali (present in glass containers), the above reaction is catalysed. It is, therefore, stored in wax-lined glass or plastic vessels in dark. Urea can be added as a stabiliser. It is kept away from dust because dust can induce explosive decomposition of the compound.
9.7.6 Uses
Its wide scale use has led to tremendous increase in the industrial production of H2O2. Some of the uses are listed below:
(i) In daily life it is used as a hair bleach and as a mild disinfectant. As an antiseptic it is sold in the market as perhydrol.
(ii) It is used to manufacture chemicals like sodium perborate and per-carbonate, which are used in high quality detergents.
(iii) It is used in the synthesis of hydroquinone, tartaric acid and certain food products and pharmaceuticals (cephalosporin) etc.
(iv) It is employed in the industries as a bleaching agent for textiles, paper pulp, leather, oils, fats, etc.
(v) Nowadays it is also used in Environmental (Green) Chemistry. For example, in pollution control treatment of domestic and industrial effluents, oxidation of cyanides, restoration of aerobic conditions to sewage wastes, etc.