Chapter 9: Methods of Separation in Everyday LifeClass 6 Science — summary, notes, extra questions & NCERT solutions

Summary

Framed as a tour of India by a brother and sister, this chapter surveys the many methods used to separate the components of a mixture in everyday life, and why we separate — to remove an unwanted component or to obtain two useful ones. Handpicking removes small quantities of stones or husk from grains by hand, based on differences in size, colour, and shape. Threshing beats harvested stalks to separate grains from them. Winnowing separates heavier grains from lighter husk by dropping the mixture in a flow of wind so the wind blows the husk away. Sieving uses a sieve to separate solid components of different sizes, such as bran from flour. To separate a soluble solid from a liquid, evaporation is used: when salt water is heated or left in the sun, the water evaporates and leaves the salt behind, which is how salt is obtained from seawater. Sedimentation is the settling of a heavier insoluble component at the bottom of a liquid, and decantation is gently pouring off the liquid above the settled matter, though decantation does not separate everything completely. Filtration passes a mixture through a filter such as a cloth or filter paper, whose tiny pores hold back insoluble solids (the residue) and let the liquid (the filtrate) pass. Churning separates lighter butter from buttermilk by spinning curd. Magnetic separation uses a magnet to pick out magnetic substances such as iron nails from a mixture. The chapter stresses that a mixture with more than two components needs a combination of several methods, and connects the science to traditional practices, recycling, and reducing river and ocean pollution.

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