Colloids

In a colloid, the size of particles is neither too small like in true solution and neither too large like in the suspension (1 - 100 nm).

Hence, there appear to be a homogeneous mixture but they are an actually heterogeneous mixture

 

Examples of Colloids

Soap Solutions, Milk, Ink, blood

 

Why is Milk a colloid?

If we examine a drop of milk under a microscope

We see small particles of fat floating in liquid which do not dissolve in liquid.


Types of Colloids

There are different types of Colloids depending on the Dispersed Phase (solute) and Dispersing Medium (solvent) , like

  • Sol - Tiny solid particles in liquid.   Example - Blood, Mud
  • Solid Sol - Tiny solid particles in solid . Example - Coloured Gemstones (like Ruby), Milky Glass
  • Aerosols - A solid or a liquid in dispersed in gas. Example - Fog, Smoke
  • Emulsions - Minute droplets of one  liquid in dispersed in another liquid (but is not miscible in it) . Example - Milk, Butter
  • Foam  - Gas  in dispersed in liquid. Example - Fire Extinguisher foam, Soap Bubbles, Beer Foam
  • Solid Foam  - Gas  in dispersed in Solid. Example - Sponge, Bread
  • Gel - Gel is a semi-solid, it is a  continuous network of solid particles in a liquid m edium. The cross linked structure of the solid in the liquid makes it behave like a solid. Example - Fruit jelly, Hair Gel

Examples of Colloids

 

Type Dispersed Phase Dispersing Medium Example
Aerosol Liquid Gas Fog, Clouds, mist
Solid Gas Smoke, automobile, exhaust
Sol Solid Liquid Milk of magnesia, mud
Solid Sol Solid Solid Coloured gemstone, milky glass
Foam Gas Liquid Shaving Cream
Gas Solid Foam, rubber, sponge, Pumice
Emulsion Liquid Liquid Milk, face Cream
Gel  Liquid Solid Jelly, cheese, butter

 

Properties of Colloid

  • It is a heterogeneous mixture
  • Size of particles is neither too small nor too large (1 - 100nm) but are too small to be seen by the naked eye
  • However, particles are large enough to scatter a beam of light; Tyndall Effect
  • Particles are stable , they do not settle down when left undisturbed.

 

Check the Difference between Solution, Suspension and Colloids

 

  1. Class 9
  2. Chapter 2 Class 9 - Is Matter Around Us Pure

About the Author

CA Maninder Singh's photo - Founder at Teachoo
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo