Chapter 5 — Exploring Mixtures and their Separation

Chapter 5 of the Class 9 Science NCERT textbook, "Exploring Mixtures and their Separation", covers mixtures and their separation, classifying them as solutions, suspensions, or colloids and teaching techniques like crystallization, distillation, paper chromatography, sublimation, centrifugation, and coagulation.

• Classifying Mixtures — Mixtures are homogeneous (solutions) or heterogeneous (suspensions, colloids), distinguished by particle size: solutions below 1 nm, colloids 1 to 1000 nm, and suspensions above 1000 nm.
• Concentration and Solubility — The amount of solute is expressed as mass by mass, mass by volume, or volume by volume percentage. Solubility of solids generally rises with temperature, while solubility of gases in liquids falls.
• Separation Techniques — Components are separated by matching a method to their properties: crystallization, distillation, and paper chromatography for solutions, and separating funnel, sublimation, centrifugation, and coagulation for heterogeneous mixtures.
• The Tyndall Effect — Colloids and suspensions scatter a beam of light passing through them while true solutions do not; this Tyndall effect is a simple way to tell these mixture types apart.

1. 01Mixtures are classified as homogeneous (solutions) or heterogeneous (suspensions, colloids); particle size distinguishes them: solutions < 1 nm, colloids 1–1000 nm, suspensions > 1000 nm.
2. 02Concentration of a solution is expressed as mass by mass (% m/m), mass by volume (% m/v), or volume by volume (% v/v) percentage.
3. 03Solubility of solid solutes generally increases with temperature, while solubility of gases in liquids decreases with temperature.
4. 04Crystallization separates or purifies solids from saturated solutions; distillation separates miscible liquids with boiling points differing by at least 25 °C.
5. 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.
6. 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.