At Nani's house, grains are cleaned of stones and husk by hand. Why bother — and are there faster ways?
Key idea
Handpicking
Picking out unwanted particles from a mixture by hand
based on differences in size, colour, and shape.
When it works best
When the unwanted particles are few in number and easy to spot — like picking stones or husk out of grain, or black pepper out of pulao.
Key idea
Threshing and Winnowing
1
Threshing
Separating grains from harvested stalks by beating them — traditionally on a wooden log, or with a threshing machine today.
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2
Winnowing
Tossing threshed grain into the wind using a soop (bamboo tray) — lighter husk blows away while heavier grains fall close by.
Key idea
Sieving
A sieve has holes of a certain size. Fine particles pass through, while larger particles stay on top.
When to use it
Best when a solid-solid mixture's parts differ in size — like flour and bran, or pebbles and sand at a construction site.
Key idea
Evaporation: Getting Salt from Seawater
Seawater is kept in shallow pits exposed to sunlight and air. After some days the water evaporates completely, leaving salt behind.
Sambhar Lake, RajasthanA well-known natural source of common salt made this way — evaporation recovers the salt, but not the water, since it escapes as vapour.
Key idea
Sedimentation and Decantation
1
Sedimentation
A heavier, insoluble part of a mixture settles at the bottom of a liquid — like tea leaves settling in a pan.
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2
Decantation
Gently tilting the vessel to pour off the liquid above the settled solid — like pouring tea without disturbing the leaves. A few particles may still escape, so it isn't a complete separation on its own.
Key idea
Filtration
1
A porous material
filter paper, cloth, sand, or charcoal — traps solid particles while liquid passes through.
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2
Residue
The solid trapped on the filter.
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3
Filtrate
The clear liquid that passes through.
Key idea
Churning and Magnetic Separation
1
Churning
Using a mathni (churner) to separate butter — which floats to the top — from curd, leaving buttermilk behind.
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2
Magnetic separation
A magnet pulls out magnetic substances like iron nails from non-magnetic ones. Recyclers use large crane-mounted magnets to pull scrap iron from waste heaps.
Key idea
Why Do We Separate Mixtures?
1
To remove the unwanted
Getting rid of one or more components we don't want or can't use — like stones from grain.
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2
To use both parts
Getting two different useful components separately — like butter and buttermilk from curd. Real mixtures often need several methods applied in sequence.
Key idea
Methods of Separation, Side by Side
Method | Basis | Example
Handpicking
Size, colour, shape — Stones out of grain
Winnowing
Wind / weight — Husk from grain
Sieving
Particle size — Flour from bran
Key idea
Methods of Separation, Side by Side — continued
1
Evaporation
Boiling point — Salt from seawater
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2
Decantation
Settling + pouring — Tea from tea leaves
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3
Filtration
Particle size, using a filter — Mud from muddy water
Chapter · Key terms to remember
Key Terms
Mixture
Two or more substances mixed together.
Handpicking
Sorting by hand.
Threshing / Winnowing
Separating grain from stalk / husk.
Chapter · Key terms to remember
More Key Terms
Sieving
Separating by particle size.
Sedimentation
Heavier solid settles at the bottom.
Decantation
Pouring off the liquid on top.
Chapter · Key terms to remember
More Key Terms
Filtration
Trapping solids with a porous filter.
Residue / Filtrate
What's trapped / what passes through.
Questions for your notebook
Write these down, then discuss
1
What purpose does handpicking serve? (i) Filtration (ii) Sorting (iii) Evaporation (iv) Decantation
2
Which method commonly separates cream from milk? (i) Oil from water (ii) Sand from water (iii) Cream from milk (iv) Oxygen from air — by churning
3
Which factor is essential for filtration? (i) Apparatus size (ii) Presence of air (iii) Pore size (iv) Temperature of the mixture
Project as-is — students copy the questions, then the class discusses answers together.