Question

Explain the following giving suitable examples for each.
(i) Aerosol
(ii) Emulsion
(iii) Micelle

Answer 1

Aerosols, emulsion and micelle have particles of size between the particle size of true solution and suspension. These belong to heterogeneous types of solutions.

Complete step by step answer:
A colloidal dispersion is a suspension of small particles in a continuous medium. Here the colloidal particles are present in a medium. The phase that is present in a colloidal state is said to be a dispersed phase. The medium in which the colloidal particles are dispersed is said to be a dispersion medium. They have the property to scatter light and have low osmotic pressure. Due to these reasons the size of colloidal particles are much larger than simple small molecules like water, alcohol and also salts like${\text{NaCl}}$.
The colloidal system is divided into two types: 1. lyophilic colloids (solvent loving). 2. Lyophobic colloids (solvent fearing).

(i) Aerosol:
An aerosol is a suspension of liquid or solid particles in gas. The diameter of colloidal particles is${10^{ - 9}} - {\text{ }}{10^{ - 4}}$. Aerosols are readily observed in nature. The atmosphere of the planets in the solar system is rich in particulate matter suspension. Examples of natural aerosols are fog, mist, dust, forests and geyser systems. If the dispersion medium is water then it is known as hydrosol. There are two different kinds of aerosols; they are primary and secondary aerosols. Primary aerosols contain particles which are directly introduced into the gas. Secondary aerosols are formed by gas to particle conversion. Aerosols vary in dispersity. In a monodisperse aerosol, particles are of uniform size.

Application of Aerosol:
(1) For instrument calibration
(2) To deliver deodorants, paints and other forms of sprays.
(3) For agricultural use.
(4) For medical treatment of respiratory diseases.
(i) Emulsion: a suspension of particles of a liquid in another immiscible liquid. There are different types of emulsions such as macro emulsions, micro emulsions, mini emulsions and multiple emulsions. Pure liquids cannot form emulsions. To make one liquid table in another liquid for a suspension, an emulsifier or emulsifying agent is added.

Macro emulsions: there are two types based on the nature of dispersion phase. They are oil in water (O/W) and water in oil (W/O).
The oil in water type emulsion is a dispersion of water immiscible liquid or solution. The dispersion phase is always called oil regardless of nature. Eg mayonnaise, milk.
Water in oil (W/O) type emulsion is a dispersion of water as a dispersed phase and oil as the dispersion medium. They are also known as oil emulsions. Examples are butter, cold creams.

(ii) Micelle: It is the aggregate of amphiphilic molecules in the solution. The aggregation depends on the nature of the amphiphilic species and the medium in which they are dissolved. The molecules can be phospholipid or fatty acids. The micelle ionic head forms an outer shell which is in contact with water and the nonpolar tails are sequestered in the inner part. The factors affecting the micelle are nature and size of polar head, length of nonpolar tail, temperature and closeness of the salts included.

Applications of micelle:
(1) They are widely used in electrophoresis.
(2) Micelles are considered as emulsifiers when the surfactants are absorbed by the critical micelle concentration.
(3) They are required in the human body for the removal of lipids and fat soluble vitamins.

Note: Reverse micelles are water droplets which are formed by the action of sulphates dispersed in water. Preparation of colloidal particles can be done in two ways: breaking down the coarse aggregates into particles of colloidal size or grouping molecules into larger aggregates of colloidal size.