CBSE Class 12 Chemistry Notes: Surface Chemistry – Colloidal Solutions

Colloidal state of Matters:-

Colloidal state of matter is, a state in which the size of the particles is such (1 to 1000 nm) that they can pass through the filter paper but not through animal or vegetable membrane.

There are three types of solutions:-

1. True solutions:- the solution in which the size of solute particles is less than 10^-9 m or 1 nm (< 10^o).
   Example. solution of sugar in water.
2. Colloidal solution:– the solution in which the size of solute particles is in between 10^-9 to 10^-6 m are called colloids.
   Example. Water in milk.
3. Suspensions:- Solution is which size of solute particles is more than 10^-6 m.
   Example. Mud in water.

Dispersed Phase:-Thus, dispersed phase means the substance distributed in the dispersion medium in form of colloidal particles.

Dispersion Medium:-the medium in which the substance is dispersed in the form of colloidal particles is known as Dispersion medium.

Classification of Colloids:-

Colloids are classified in three different ways as Follows:-

1. Based on physical state of dispersed phase and dispersion medium:-Depending upon weather the dispersed phase and dispersion medium are solids, liquids are gases eight types of colloidal systems are possible.

2. Based on nature of interaction between dispersed phase and dispersion medium:-

Lyophilic Colloids:-Substances like gum, gelatin, starch, rubber, which when mixed with a suitable liquid as the dispersion medium directly form the colloidal sol are called lyophilic and the sols thus are obtained are called lyophilic sols.

Ex. Muddy water.

Lyophobic Colloids:-Substances like metals, their sulphides, when simply mixed with the dispersion medium do not form colloidal sol. Which can be only prepared by special methods only. Such substances are called Lyophobic Sols.

3. Based on the type of particles of dispersed Phase:-

1. Multimolecular Colloids:- When on dispersion of a substance in dispersion medium, a large number of atoms or smaller. Molecules of substances aggregate together to form species having size in colloidal range, the species thus formed are called Multimolecular Colloids.
   Example– Gold sol, sulphur sol.
2. Macromolecular Colloids:-When certain substances having big size molecules called macro molecules having large molecular masses are dissolved in a suitable liquid, they form a solution in which the molecules of substances have size in colloidal range are called macromolecule or Colloids
   Example– Polyethene, nylon etc.
3. Associated colloids:-the substance which when dissolved in a medium at low concentrations behave as higher concentration exhibited colloidal state properties due toformation of aggregated particles are called associated colloids
   The aggregated particles thus formed are called micelles.

Kraft’s temperature:- the formation of micelles takes place only above a particular temperature is called as the kraft’s tempreture.

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