Summary
Chapter 5 of Class 9 Science (NCERT 2026-27 'Exploration' edition) covers mixtures and their separation, classifying mixtures as solutions, suspensions, or colloids and teaching techniques like crystallization, distillation, paper chromatography, sublimation, centrifugation, and coagulation.
Class 9 Science Chapter 5 'Exploring Mixtures and their Separation' classifies mixtures as homogeneous (solutions) or heterogeneous (suspensions, colloids) based on composition and particle size. It explains concentration expressions — mass by mass, mass by volume, and volume by volume percentages — and solubility curves. Separation techniques covered include crystallization, distillation, paper chromatography (for homogeneous mixtures), and separating funnel, sublimation, centrifugation, and coagulation (for heterogeneous mixtures). The Tyndall effect, where colloids and suspensions scatter light while true solutions do not, is also explained.
Key points & formulas
- 01Mixtures are classified as homogeneous (solutions) or heterogeneous (suspensions, colloids); particle size distinguishes them: solutions < 1 nm, colloids 1–1000 nm, suspensions > 1000 nm.
- 02Concentration of a solution is expressed as mass by mass (% m/m), mass by volume (% m/v), or volume by volume (% v/v) percentage.
- 03Solubility of solid solutes generally increases with temperature, while solubility of gases in liquids decreases with temperature.
- 04Crystallization separates or purifies solids from saturated solutions; distillation separates miscible liquids with boiling points differing by at least 25 °C.
- 05Sublimation separates substances that convert directly from solid to vapour (e.g., camphor) without passing through the liquid state; immiscible liquids are separated using a separating funnel.
- 06Centrifugation spins mixtures at high speed to separate heavier particles; coagulation uses a coagulant (e.g., alum) to clump fine suspended particles so they settle; the Tyndall effect is the scattering of light by colloid or suspension particles.
Frequently asked questions
01What is the difference between a solution, a suspension, and a colloid?
A solution is a homogeneous mixture with solute particles smaller than 1 nm that do not scatter light or settle. A suspension is a heterogeneous mixture with particles larger than 1000 nm that are visible to the naked eye, settle on standing, and scatter light. A colloid has intermediate particle size (1–1000 nm), appears homogeneous, does not settle, but scatters light (Tyndall effect). Examples: salt solution (solution), muddy water (suspension), milk (colloid).
02Which separation technique is used to separate two miscible liquids like acetone and water?
Distillation is used to separate two miscible liquids whose boiling points differ by at least about 25 °C. Acetone boils at 56 °C and water at 100 °C, so when the mixture is heated, acetone vaporises first, is cooled in a condenser, and collected as a pure liquid, leaving water in the distillation flask.
03What is the Tyndall effect and which types of mixtures show it?
The Tyndall effect is the scattering of light by dispersed particles, making the path of a light beam visible. Colloids (e.g., milk) and suspensions (e.g., muddy water) show the Tyndall effect because their particles are large enough to scatter light. True solutions (e.g., salt solution) do not show this effect because their particle size is less than 1 nm.
04Is the NCERT Class 9 Science Chapter 5 PDF free to download?
Yes, the NCERT Class 9 Science Chapter 5 PDF is completely free to download on cbseprepmaster.com.
More chapters in Exploration
This is the complete Exploration Chapter 5 as published by NCERT — every diagram, solved example, and exercise included, free. Browse all NCERT Class 9 textbooks.
Read offline with notes, solutions & mock tests
CBSE Prepmaster — free on iOS & Android