The primary sector involves activities that:

produce goods directly from nature

Which of these belongs to the secondary sector?

Manufacturing cloth from cotton in a factory

What is handpicking, and when is it useful?

Handpicking is separating a component from a mixture by hand based on size, colour, and shape; it is useful when the component to be removed is present in small quantities.

Threshing is the process of beating harvested stalks to separate the grains attached to them.

When is sieving used?

Sieving is used when the components of a solid mixture have different particle sizes, such as separating bran or stones from fine flour.

How is salt obtained from seawater?

Seawater is kept in shallow pits and exposed to sunlight and air; the water evaporates, leaving behind a solid mixture from which common salt is obtained.

What is the difference between sedimentation and decantation?

Sedimentation is the settling of a heavier insoluble component at the bottom of a liquid, while decantation is the gentle pouring off of the liquid above the settled matter.

What is filtration, and what are the residue and filtrate?

Filtration separates insoluble solids from a liquid using a filter; the solid left on the filter is the residue and the clear liquid that passes through is the filtrate.

What is churning used to separate?

Churning is used to separate lighter butter from buttermilk by spinning curd, with the butter floating to the top.

What is magnetic separation?

Magnetic separation is the separation of magnetic substances, such as iron nails, from non-magnetic substances using a magnet.

How would you separate a mixture of more than two components?

A mixture with more than two components needs a combination of several methods of separation, applied in a suitable sequence based on the properties of the components.

Methods of Separation in Everyday Life

Q: What is winnowing?

Winnowing is the method of separating heavier grains from lighter husk by dropping the mixture in a flow of wind so that the wind blows the husk away.

Class 6 Science · Curiosity · Chapter 9

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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.

Handpicking, threshing, winnowingSievingEvaporation and obtaining saltSedimentation, decantation, filtrationChurning and magnetic separation

Key terms

Handpicking

Separating small quantities of one component from a mixture by hand, based on differences in size, colour, and shape.

Threshing and winnowing

Threshing beats stalks to separate grains; winnowing separates heavier grains from lighter husk using wind or by blowing air.

Sieving

Separating the components of a solid mixture by their different particle sizes using a sieve.

Evaporation

Separating a dissolved solid from a liquid by letting the liquid turn to vapour, as in obtaining salt from seawater.

Sedimentation and decantation

Sedimentation is the settling of a heavier insoluble component at the bottom of a liquid; decantation is gently pouring off the liquid above it.

Filtration and magnetic separation

Filtration separates insoluble solids from a liquid using a filter's pores; magnetic separation uses a magnet to pick out magnetic substances.

Extra questions & answers

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Picking small stones from grains by hand, based on size, colour, and shape, is called:

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