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What are the common methods of separating mixtures?

Class 6 ScienceNCERT chapter: Methods of Separation in Everyday Lifeइसे हिंदी में पढ़ें

Exam-ready answer

Common methods of separation are handpicking, threshing, winnowing, sieving, sedimentation and decantation, filtration, evaporation and churning. Each method uses a difference between the components of a mixture, such as size, weight, colour or whether a substance dissolves in water. We separate mixtures to remove unwanted or harmful parts, or to obtain a useful component.

Explanation

Handpicking removes stones, husk or spoilt grains from rice and pulses because they differ in size, colour or shape. Threshing separates grain from stalks by beating the harvested stalks. Winnowing separates heavier grain from lighter husk: when the mixture is dropped from a height, wind carries the husk away while the grain falls close by. Sieving separates particles of different sizes, such as bran from flour.

When muddy water is left undisturbed, the heavier soil particles settle at the bottom; this is sedimentation. Pouring off the clear water above without disturbing the settled layer is decantation. Filtration removes fine insoluble particles by passing the mixture through a filter, such as filter paper or a cloth, which lets the liquid through but holds back the solid; tea leaves are separated from tea in this way.

Evaporation separates a dissolved solid from water. Heating salt water drives off the water as vapour and leaves the salt behind, which is how salt is obtained from seawater in shallow pans. Churning separates butter from curd: stirring it hard makes the lighter butter collect and float on top. Often two or more methods are used one after another.

Points to remember

  1. Handpicking and sieving use differences in size, colour or shape of particles.
  2. Threshing separates grain from stalks; winnowing separates heavier grain from lighter husk using wind.
  3. Sedimentation: heavier insoluble particles settle down; decantation: pouring off the liquid above.
  4. Filtration: insoluble solids are held back by a filter while the liquid passes through.
  5. Evaporation recovers a dissolved solid such as salt; churning separates butter from curd.

Exam tip

For each method, write one line on the property it uses and one everyday example, such as 'winnowing: husk is lighter than grain'. Drawing the filtration set-up with labels earns easy marks.

Questions students also ask

Why do we need to separate mixtures?
We separate mixtures to remove unwanted parts, such as stones from rice, to remove harmful parts, such as mud from drinking water, or to obtain a useful substance, such as salt from seawater or butter from curd.
Can salt be separated from salt water by filtration?
No. Salt dissolves completely in water, so its particles pass through the filter paper along with the water. Filtration only removes insoluble particles. Salt is recovered by evaporation, which removes the water as vapour and leaves the salt behind.
Why is winnowing done in a breeze?
Winnowing works because husk is much lighter than grain. When the mixture is dropped from a height, the moving air carries the light husk to a distance, while the heavier grain falls straight down. Without wind, both would fall in the same heap.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.