Separation of Substances

Pure substances are rarely found in nature — most are mixtures. We need to separate to get useful components, remove impurities, and process food. Methods depend on properties: size, density, magnetic attraction, solubility, boiling point.

Handpicking: manually remove unwanted items (remove stones from dal). Threshing: separate grain from stalks by beating on hard surface (paddy, wheat). Winnowing: use wind to separate light chaff from heavier grain (hold high, pour — wind blows chaff away). These are ancient Indian farming techniques.

Sieving: separate by particle size (flour sieve, construction sand). Fine particles fall through, coarse stay. Filtration: separate insoluble solid from liquid using filter paper/cloth. Example: filter dirty water — mud stays on filter, water passes through.

Evaporation: heat a solution → liquid evaporates, solid remains. Used to recover salt from seawater (saltpans). Distillation: separate two liquids by boiling — the liquid with lower boiling point evaporates first, condenses and is collected. Used to purify water (distilled water).