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Hydrogen Peroxide

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Hydrogen Peroxide - Lesson Summary

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 111.5 0.

 
In solid state at a temperature of 110 K, it has a dihedral angle of 90.2 0.
 


Preparation:
In laboratories, hydrogen peroxide is prepared from barium peroxide or acidified sulphate solution.

BaO 2.8H 2O(s) + H 2SO 4(aq) → BaSO 4(s) + H 2O 2(aq) + 8H 2O(I)

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.

2HSO - 4 (aq)   Electrolysis →   HO 3SOOSO 3H (aq)
        Hydrolysis → 2HSO - 4 (aq) + 2H + (aq) + H 2O 2(aq)

Commercially, hydrogen peroxide is prepared by auto-oxidation of 2-ethylanthraquinol. It involves alternate oxidation and reduction of 2-ethylanthraquinol.


 
Physical properties:
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.
 
Chemical Properties:
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.

2Fe 2+ (aq) + 2H + (aq) + H 2O 2 (aq) → 2Fe 3+ (aq) + 2H 2O(I)

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 + H 2O 2 → O 2 + NaCl + H 2O

In basic media:
As an oxidizing agent, hydrogen peroxide reacts with ferric ions to form ferrous ions.

2Fe 2+ + H 2O 2 → 2Fe 3+ + 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 

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