Hydrogen peroxide is a very pale blue liquid and appears colourless in a dilute solution. It is naturally produced in organisms as a by-product of oxygen metabolism.
Structurally, the hydrogen peroxide molecule is non-planar. It has an open book structure. The presence of lone pairs of electrons on the oxygen atoms, and the hydrogen bonding gives the molecule a different structure in gaseous and solid phases.
In gaseous state, hydrogen peroxide has a dihedral angle of 111.50
In solid state at a temperature of 110 K, it has a dihedral angle of 90.20
In laboratories, hydrogen peroxide is prepared from barium peroxide or acidified sulphate solution.
O(s) + H2
(aq) → BaSO4
(s) + H2
(aq) + 8H2
Hydrogen peroxide also obtained from 50% sulphuric acid solution on electrolytic oxidation. During electrolysis, hydrogen peroxide is formed at the anode. Peroxydisulphuric acid is formed as a by-product at the anode. Hydrogen gas is evolved at the cathode.
(aq) + 2H+
(aq) + H2
Commercially, hydrogen peroxide is prepared by auto-oxidation of 2-ethylanthraquinol. It involves alternate oxidation and reduction of 2-ethylanthraquinol.
It has a melting point of 272.4 K, a boiling point of 432 K, a vapour pressure of 1.9 mmHg, a solid density of 1.64 gram/cc and a liquid density of 1.44 gram/cc. Its viscosity is slightly higher than water.
It acts as an oxidizing as well as a reducing agent in both, acidic and basic media.
In an acidic medium:
It acts as an oxidizing agent, reacts with ferrous ions to form ferric ions.
(aq) + 2H+
(aq) + H2
(aq) → 2Fe3+
(aq) + 2H2
As a reducing agent, it reacts with sodium hypo chloride and yields water, sodium chloride salt and oxygen. This reaction is also used in laboratories to prepare oxygen.
NaOCl + H2
+ NaCl + H2
In basic media:
As an oxidizing agent, hydrogen peroxide reacts with ferric ions to form ferrous ions.
+ 2OH -
The demand for hydrogen peroxide has increased as it has found widespread use in pollution control treatment of domestic and commercial effluents.
Uses of Hydrogen peroxide:
- As a mild disinfectant
- As a cleanser
- As a bleaching agent in the textile, paper pulp, leather, oils and fats industries
- As a pollution control agent in the treatment of domestic and industrial effluents, oxidation of cyanides, restoration of aerobic conditions to sewage wastes...etc