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’.

Image source: chemistrylibre

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 -112.4^oC into liquid while oxygen condenses at -182.5^oC.
• Hence, ozone and oxygen can be separated in pure state.

Image source: ozonesecreteriat

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.

Image source: researchgate

• 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.

References: 

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