Ch 2 classifies matter into pure substances (elements and compounds) and mixtures (homogeneous and heterogeneous). Students learn about solutions, suspensions, colloids, and advanced separation techniques.
Pure substances have fixed composition and properties: elements (Fe, O₂, Au) and compounds (H₂O, CO₂, NaCl). Mixtures have variable composition: homogeneous (solutions — uniform, e.g., salt water) and heterogeneous (non-uniform, e.g., sand+water).
Solution: solute + solvent, particle size < 1 nm, transparent, doesn't scatter light, doesn't settle. Suspension: particle size > 100 nm, cloudy, settles over time, can be filtered. Colloid: 1–100 nm, appears homogeneous, scatters light (Tyndall effect), doesn't settle — examples: milk, fog, smoke.
Evaporation: dissolved solid from liquid. Chromatography: separating pigments/dyes. Distillation/fractional distillation: separating liquids with different boiling points. Centrifugation: separating fine suspended particles (cream from milk). Crystallisation: obtaining pure solid from solution.
Download: https://ncert.nic.in/textbook/pdf/iesc102.pdf | Complete book: https://ncert.nic.in/textbook/pdf/iesc1ps.zip
When a beam of light passes through a colloidal solution, the light is scattered by the colloidal particles, making the path of light visible. This is the Tyndall effect. Example: light beam visible in fog or a dusty room. True solutions do not show this effect.
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