NCERT Solutions for Class 9 Science Chapter 5: Exploring Mixtures and their Separation – Free PDF Download

Chapter 5 of Class 9 Science Exploration is Exploring Mixtures and their Separation, the first chemistry chapter of the book. It covers how substances combine into mixtures, the different kinds of mixtures, and the practical techniques used to separate them. These Class 9 Science Chapter 5 solutions are also useful as quick revision notes before exams.

Pure Substances and Mixtures

A pure substance has a fixed composition (elements or compounds). A mixture contains two or more substances combined in variable proportions, without any fixed composition.

Homogeneous and Heterogeneous Mixtures

A homogeneous mixture has uniform composition throughout (e.g. salt dissolved in water) — you cannot see the separate components. A heterogeneous mixture has visibly distinct components or regions (e.g. sand in water).

Solutions, Suspensions, and Colloids

• Solution — a homogeneous mixture where the solute is completely dissolved in the solvent; particles are too small to scatter light or settle.
• Suspension — a heterogeneous mixture where particles are large enough to be visible and settle over time (e.g. muddy water).
• Colloid — particle size is between a solution and a suspension; particles don’t settle but scatter light (Tyndall effect), e.g. milk, fog.

Expressing Concentration

The concentration of a solution can be expressed as mass by mass percentage, mass by volume percentage, or volume by volume percentage — describing how much solute is present relative to the solution.

Separation Techniques

• Crystallisation — obtaining pure solid crystals from a solution by controlled cooling/evaporation, better than simple evaporation for heat-sensitive or impure substances.
• Distillation — separates miscible liquids with different boiling points, by heating, then condensing the vapour.
• Paper chromatography — separates components of a mixture (e.g. dyes) based on differing solubility and movement through paper.
• Sublimation — separates a sublimable solid (e.g. camphor, ammonium chloride) from a non-sublimable one by direct solid-to-gas conversion on heating.
• Centrifugation — spins a mixture at high speed to separate components by density (e.g. separating cream from milk).
• Coagulation — causes colloidal particles to clump together and settle, used to separate colloidal particles from a colloid.

Frequently Asked Questions

What is the key difference between a solution, a suspension, and a colloid?
In a solution, particles are fully dissolved and invisible; in a suspension, particles are large, visible, and settle over time; in a colloid, particle size is intermediate — particles don’t settle but scatter light (Tyndall effect).

Why is distillation used instead of simple evaporation to separate a mixture of two liquids?
Because evaporation only recovers a dissolved solid by removing the liquid solvent; distillation separates two or more liquids with different boiling points by selectively vaporising and condensing them one at a time.

What everyday example shows the Tyndall effect?
A beam of light passing through fog or a beam of sunlight through dusty air becoming visible, both examples of light scattering by colloidal particles.

Written by Satish

NCERTBooks.org is an independent educational resource run by a small team focused on making official NCERT textbooks easy to find, read, and download for students, parents, and teachers across India. We are not affiliated with NCERT or the Ministry of Education -- we organise publicly available NCERT content by class and subject, verify links against official sources, and build tools (like our in-browser reader) that make studying more convenient. Every guide we publish is written and reviewed by our team based on the actual NCERT curriculum and syllabus.