Is Matter Around us Pure?

04 Suspensions and Colloids

A suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it.
The particles have a diameter greater than 100 nm and hence are visible to the naked eye.
Examples of suspensions are: Chalk-water mixture, Muddy water, Milk of Magnesia.
If mud is mixed in a glass full of water, it will form a heterogeneous mixture whose components can be identified easily.
After some time particles of mud settle down due to gravity. The particles in suspension are larger than the particles in a solution.

Properties of a Suspension:

The important characteristic properties of a suspension are as follows:

A suspension is a heterogeneous mixture.
The particles of a suspension do not pass through a filter paper. So, a suspension can be separated by filtration.
The size of solute particles in a suspension in quite large. It is larger than 100 nm in diameter. Hence could be seen by the naked eye.
The particles of a suspension can be seen easily.
A suspension scatters a beam of light passing through it.
The suspensions are unstable.
The particles of a suspension settle down after some time.

A colloidal solution is said to be intermediate state of the solution and the suspension.
It is neither a true solution nor a suspension.
The medium of colloidal solution is known as dispersed medium and the particles dissolved are called dispersed phase.
In milk, water is dispersion phase and fats, proteins etc. are dispersed phase.
In fog, water droplets from the dispersed phase and air is dispersing medium.

Properties of Colloids:

The important characteristic properties of colloids or colloidal solutions are as follows:

A colloid or colloidal solution appears to be homogeneous but actually it is heterogeneous.
The size of particles in a colloid or colloidal solution is bigger than those in a true solution but smaller than those in a suspension. It is between and in diameter.
The particles of most of the colloids or colloidal solutions cannot be seen even with a microscope.
The particles of a colloid or colloidal solution can pass through a filter paper. So, a colloid cannot be separated by filtration.
The colloids or colloidal solutions are quite stable. The particles of a colloid do not separate out on keeping.
A colloid or colloidal solution scatters a beam of light passing through it.
Colloids can be distinguished from solutions using Tyndall effect which is the scattering of light through a colloidal solution. The particles are termed as colloidal particles and the mixture formed is known as colloidal dispersion formed by mixture of liquid, solid and gases.
The different types of colloidal solutions are:
- Aerosols: Solid or liquid mixed with gas; Example: fog (liquid in gas)
- Sols: Solid mixed with liquid; Example: Paint
- Emulsion: Liquid with liquid; Example: oil and water
- Gel: liquid in solid; Example: Fruit jelly

The Classification of Colloids:

Technical name Of colloid	Dispersed Phase	Dispersion medium	Examples
1. Sol	Solid	Liquid	Ink, Soap solution, Starch solution, Most paints
2. Solid sol	Solid	Solid	Coloured gemstones (like Ruby)
3. Aerosol	(i) Solid (ii) Liquid	Gas Gas	Smoke, Automobile exhausts Hairspray, Fog, mist, Clouds
4. Emulsion	Liquid	Liquid	Milk, Butter, Face cream
5. Foam	Gas	Liquid	Fire-extinguisher foam, Soap bubbles, Shaving cream, Beer foam
6. Solid foam	Gas	Solid	Insulating foam, Foam rubber, sponge, Bread
7. Gel	Solid Continuous network Solid in liquid	Liquid Of	Jellies, Gelatin, Hair gel

Difference between Colloid and Suspension:

Suspension	Colloid
It is a form of homogeneous solution	It is a form of heterogeneous solution
Particle size greater than 1000 nm	Particle size range from1-1000 nm
Particles settle down well	Particles do not separate
Can be separated by filtration	Cannot be separated by filtration
May scatter light	Shows Tyndall effect (scatters light)
Opaque	Translucent
Easily visible through naked eye	Not visible through naked eye