OZONE

Ozone is an unstable triatomic molecule of oxygen. In 1866, J. Soret, demonstrated that ozone was an allotrope of oxygen. Ozone is formed from atmospheric oxygen by lightning flashes. Small fractions of ozone are also formed around electrical machinery when they are in operation. Ozone exists in a layer at a height of about 25km above earth surface.

 

Preparation of Ozone

Ozone is prepared from oxygen by the use of the silent electrical discharge.

Dry oxygen is passed through the space between the glass tubes. Each tube is coated with tin – foil which is connected to the terminals of an induction coil.Silent electrical discharge is preferred because sparking would generate heat, which decomposes the ozone. An ozoniser is used for ozonising oxygen.

The ozonised oxygen should not be allowed to come into contact with rubber because it is attacked by ozone.

 

Physical Properties of Ozone

1. Ozone is a pale blue gas at ordinary temperature and pressure.
2. It has a characteristic smell like that of dilute chlorine.
3. It is poisonous at concentrations above 100 parts per million.
4. Pure Ozone can be obtained as blue liquid by cooling ozonised oxygen to -112°C.

 

Chemical Properties of Ozone

1) Ozone has similar chemical properties as oxygen except that it is more reactive. It decomposes into ordinary oxygen on heating.

2) Ozone is a more powerful oxidising agent than oxygen. It oxidises lead (II) sulphide and hydrogen sulphide to tetraoxosulphate (VI).

It also oxidises sulphur (IV) oxide to sulphur(VI) oxide.

Oxygen is formed as a by-product in these reactions.

3) Ozone liberates iodine from potassium iodide in acidic solution.

 

Uses of Ozone

1. Ozone is a good bleaching agent
2. It is used as a disinfectant in water and sewage purification.
3. It is used for ventilating areas which get very little fresh air.
4. It is used in air conditioning plants.

 

Allotropy of Oxygen and Ozone

Oxygen and ozone are allotropes. Allotropy is the ability of an element to exist in more than one form in the same physical state.

 

Differences between Oxygen and Ozone

 

Oxygen

1. Insoluble in turpentine.
2. No effect on rubber.
3. Has no effect on potassium iodide solution.
4. Oxidising agent.
5. Heat has no effect.
6. No effect on mercury at room temperature.

 

Ozone

1. Absorbed by turpentine.
2. Attacks rubber.
3. Liberates iodine from potassium iodide solution.
4. Powerful oxidising agent.
5. Heat converts ozone into oxygen.
6. Makes mercury wet glass.