Ozone and its preparation

  • Elemental oxygen exists as a triatomic molecule (O3) known as ozone in addition to di-oxygen.
  • The existence of an element in more than one modification in the same physical state is referred to as allotropy.
  • Ozone is an allotropic form of oxygen which is present in the upper atmosphere about 20 km above the surface of the earth.

Preparation of Ozone

  • Ozone can be conveniently prepared by passing silent electric discharge through pure, cold and dry oxygen.
  • The apparatus used for this purpose is called ozoniser.

3O2     →    2O3;     ∆ H= +284 KJ

  • The reaction is endothermic and energy is absorbed.
  • The silent (sparkles) electric discharge produces less heat. This prevents the local rise in temperature which may decompose ozone back to oxygen.
  • Two types of ozonisers that are commonly used for the production of ozone are:

a)Siemen’s ozonizer

b)Brodie’s ozoniser

A) Siemen’s ozoniser

  • It consists of two concentric metal tubes sealed together at one end.
  • The inner side of the inner tube and outer side of outer tube is coated with tin foil and connected to one terminal each of an induction coil.
  • A slow stream of pure and dry oxygen is passed through the annular space and is subjected to the silent electric discharge.
  • As a result, 10-15% ozone is formed.
  • It comes out along with oxygen called ‘ozonized oxygen’.

Ozone - Wikiwand            Ozone - Chemistry LibreTexts

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B) Brodie’s ozoniser

  • The principle of this ozonizer is similar to Siemen’s ozoniser.
  • Two platinum electrodes are dipped in the sulphuric acid and connected to an induction coil.
  • A current of pure dry oxygen is passed through the annular space and subjected to silent electric discharge.
  • As a result, 15-20% of ozone is formed.
  • The ozone so formed is along with oxygen called ‘ozonized oxygen’.
  • Ozonized oxygen can be converted to pure ozone by lowering the temperature of the ozone condenses at -112.4oC into liquid while oxygen condenses at -182.5oC.
  • Hence, ozone and oxygen can be separated in pure state.

20 Questions and Answers | Ozone Secretariat

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Uses of Ozone

  • It is used as germicide and disinfectant. So, it finds use in sterilization of water.
  • It is used to purify the atmosphere in crowded places like cinema halls, heavy traffic stations and in underground tunnels and mines.

Major biological effects of ozone therapy. | Download Scientific Diagram

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  • It is also used as bleaching agent for fabrics, oils, ivory, wax, etc.
  • It is also used in laboratory to prepare potassium permanganate and to locate the double bond in organic compounds.
  • It is used in aquaculture and fish farming.
  • It is used for surface treatment such as semiconductor manufacture, inorganics production.
  • It is used for food processing like rinsing water, food preservation.


i) https://www.brainkart.com/article/Ozone–Laboratory-preparation,-Properties,-Uses,-structure,-layer_2723/

ii) https://chemicalnote.com/ozone-preparation-uses-test-ozone-layer-depletion/

Ozone and its preparation