Question

Write briefly about the preparation of colloids by chemical methods.

Answer 1

Hint: Colloidal mixtures: It is defined as the mixture in which the tiny particles are suspended throughout another substance.
There are two ways by which colloids are formed i.e. dispersion and condensation methods.

Complete step by step solution:
First of all we will talk about colloidal particles, dispersed and dispersion mediums.
Colloidal mixtures: It is defined as the mixture in which the tiny particles are suspended throughout another substance.
Dispersion phase: The phase in which the colloidal particles exist, are known as dispersed phases.
Dispersion medium: The medium in which the colloidal particles are distributed, is known as dispersion medium.

Dispersed phase	Dispersion medium	Name of the colloid	Example
Solid	Solid	Solid sol	Alloys
Solid	Liquid	Sols	Paints, jellies
Solid	Gas	Aerosol	Dust, smoke
Liquid	Solid	Solid emulsion	Butter, cheese
Liquid	Liquid	emulsion	Milk, cream
Liquid	Gas	Liquid aerosol	Mist, cloud, foam
Gas	Solid	Solid foam	Marshmallow
Gas	liquid	Foam	Whipped cream

There are two ways by which colloids are formed i.e. dispersion and condensation methods.
Dispersion method: In this method large molecules are broken down into small molecules. There are four ways in which dispersion method can be carried out:
Mechanical dispersion: In this process large colloids particles are first ground to coarse the particles.
Electrical dispersion: This process is used to prepare colloids of platinum, gold and silver.
Peptization dispersion: This method is used for converting a precipitate into sols. In this method mix the precipitate with the dispersion medium in the presence of electrolyte.
Condensation method: In this method small particles aggregate together to form the large particles.
Double decomposition technique: This is used to form arsenic sol. In this method hydrogen sulphide is passed through a solution of arsenious oxide.
Oxidation technique: In this method colloidal solution of sulphur is allowed to pass through an aqueous solution of sulphur dioxide. By this method sulphur sol is formed.
Reduction technique: By this method colloidal solutions of metals such as gold, silver and platinum are formed. In this method, a reducing agent is used for the reduction of salt solution of these metals.
Hydrolysis technique: This method is used for the preparation of colloidal solution of ferrous hydroxide. It involves the boiling water to obtain a reduced solution of ferric chloride.

Note:
Emulsions are of two types: water in oil it is represented as w/o and oil in water it is represented as o/w. In w/o type emulsions the dispersed phase is water and dispersion medium is oil. For example: butter. In o/w type emulsions the dispersed phase is oil and dispersion medium is water. For example: milk.