COLLOIDAL SOLUTION(CBSE 9TH NCERT TEXT SCIENCE)

 

Colloidal Solution (Colloids)

• A colloidal solution is a heterogeneous mixture in which very small particles of one substance are evenly spread out in another substance.

• The particle size in colloids is between true solution and suspension (i.e. 1 nm – 1000 nm).

• These particles are small enough that they do not settle down on their own and cannot be seen with the naked eye, but can scatter light.

Characteristics of Colloids

• Heterogeneous mixture – appears homogeneous to the naked eye.

• Stable – particles do not settle down on standing.

• Tyndall Effect – colloidal particles scatter a beam of light.

• Particles cannot be filtered using ordinary filter paper but can be separated by special filters (ultrafiltration).

• Brownian Motion – colloidal particles show continuous zig-zag movement.

Examples of Colloids in Daily Life

• Milk → fat in water (emulsion)

• Fog → water droplets in air (aerosol)

• Butter → water in fat (emulsion)

• Smoke → solid particles in air

Types of Colloids (Based on Phases)

Dispersed Phase	Dispersion Medium	Example

Solid

Gas

Smoke, Dust in Air

Liquid

Gas

Fog, Mist, Cloud

Gas

Liquid

Foam, Shaving Cream

Solid

Liquid

Starch Solution, Muddy Water

Liquid

Liquid

Milk, Emulsion

Solid

Solid

Coloured Glass, Gemstones

Important Note for Exams

• True solution → particle size < 1 nm, transparent (e.g., sugar in water)

• Colloid → particle size 1–1000 nm, scatters light (e.g., milk)

• Suspension → particle size > 1000 nm, particles settle on standing (e.g., sand in water)

TYPES OF SOLUTIONS