Educational Galaxy

Methods of Separation in Everyday Life — EG's own notes, in simple words

Book: Curiosity (CBSE, Class 6)  |  Chapter 9  |  Medium: English

Diagram (labels are printed on the image): Filtration: solid grains stay in the filter paper while clear liquid drips into the flask below. A general teaching picture of a laboratory set-up.

A farmer winnowing grain — light husk blows away while heavy grain falls. A general picture about separation in daily life.

Diagram (labels are printed on the image): Choose the method by the property that differs: size (sieving), weight in wind (winnowing), solubility (evaporation vs filtration), or magnetism (magnetic separation).

What the chapter is about

Many things around us are mixtures — two or more substances mixed together without a chemical change, so each part keeps its own properties and can be separated by a physical method. Salt in water, sand in rice, tea leaves in tea and mud in water are all mixtures. We separate them to remove something harmful or unwanted, to get a useful part out, or to purify a substance.

Handpicking is the simplest method. When the unwanted part is small in amount and differs in size, shape or colour, it can be picked out by hand — stones from rice or wheat, or insects from grain. It is slow, so it suits only small quantities.

Threshing and winnowing come from farming. Threshing beats harvested crops so grains separate from stalks; modern threshers do threshing and winnowing together. Winnowing separates lighter and heavier parts using wind or blowing air: the farmer drops the mixture from a height or shakes a bamboo tray (soop) in the wind, the light husk is blown away, and the heavy grains fall straight down. Winnowing needs moving air — it cannot be done well in a closed room.

Sieving separates by size. A sieve has holes of one size: fine particles pass through, bigger ones stay back. Flour is sieved to remove bran and small stones; sand is sieved to remove gravel. The key property is particle size.

For a solid mixed in a liquid, first ask whether the solid dissolves. If it does not dissolve and is heavy, sedimentation and decantation work: leave muddy water undisturbed, the mud settles at the bottom (sedimentation), then pour out the clear water carefully without disturbing the sediment (decantation). If the solid must be removed completely, filtration is better: pour the mixture through filter paper or cloth, the solid stays on the filter as residue, and the clear liquid, the filtrate, passes through. Filtration depends on pore size — the pores must be smaller than the solid particles but let the liquid through. Nature uses the same idea: nose hair filters dust from inhaled air, and face masks filter tiny particles from the air we breathe.

If the solid is dissolved, filtration cannot help, because the dissolved solid passes through the filter with the liquid. Evaporation is the answer: heat salt water, the water turns to vapour and the salt is left behind. Salt is made from sea water this way, using the Sun's heat in shallow pans. Note the pair: filtration separates an insoluble solid from a liquid; evaporation recovers a soluble solid from a liquid.

Two more methods complete the set. Churning separates cream or butter from milk or curd by vigorous stirring or shaking — the lighter fat collects together. Magnetic separation uses a magnet to pull iron out of a mixture, for example iron powder from sawdust. And when water must be made safe to drink, several methods combine: let muddy water stand (sedimentation), filter it through cloth or paper (filtration), then boil it to kill germs — each step removes a different problem.

What you should learn

• Define mixture and give three reasons for separating one.
• Choose a method by the property that differs: amount, size, weight, solubility, magnetism.
• Tell sedimentation, decantation and filtration apart, and say when each is used.
• Explain why filtration cannot separate a dissolved solid, and why evaporation can.
• Combine methods in order for a multi-part mixture and for making muddy water safe.

Chart / Table: Choosing a separation method

Table: Choosing a separation method

Table: Filtration vs evaporation — do not mix them up

Practice set — try it yourself

1. Why can we not filter salt out of salt water?
   Hint: Think about dissolved versus undissolved.
2. Which method separates husk from grain? What property does it use?
   Hint: Think about wind and weight.
3. How would you separate sand from water in the lab?
   Hint: Think about filter paper.
4. Give one example of separation used at home.
   Hint: Think about tea, rice or flour.
5. How is common salt obtained from sea water?
   Hint: Think about sun and evaporation.

Questions with Answers

1. What is a mixture? Give two examples.
   A mixture is made by mixing two or more substances together without any chemical joining, so the parts keep their own properties and can usually be separated. Examples are salt dissolved in water, and sand mixed with rice.
2. How would you separate sand from water? Explain the method.
   Sand is insoluble in water, so filtration is used. The mixture is poured through filter paper in a funnel. The water passes through as filtrate, while the sand stays behind on the filter paper as residue.
3. Why is evaporation, not filtration, used to get salt from salt water?
   Salt dissolves in water, so it is not caught by filter paper — it passes through with the water. On heating, the water evaporates away and the salt is left behind, so evaporation recovers the dissolved solid.
4. Explain winnowing and say where it is used.
   In winnowing, a mixture of grain and husk is dropped from a height in moving air. The light husk is blown away by the wind while the heavier grain falls straight down. Farmers use it after threshing to clean grain.
5. A mixture contains stones, sand and salt. Suggest steps to separate all three.
   First, handpick the large stones. Next, stir the rest in water — the salt dissolves while the sand does not — and filter to get the sand on the paper. Finally, evaporate the filtrate to get the salt back.

More NCERT-exercise questions — extra practice

1. What purpose does handpicking serve? Choose: filtration, sorting, evaporation, decantation.
   Sorting — handpicking sorts out the unwanted part by hand. It is not filtration, evaporation or decantation.
2. Which substances are commonly separated using the churning method? Choose: oil from water, sand from water, cream from milk, oxygen from air.
   Cream from milk (and butter from curd). Churning stirs the liquid vigorously so the lighter fat collects together.
3. Which factor is usually essential for filtration? Choose: apparatus size, presence of air, pore size, temperature of the mixture.
   Pore size. The pores must be smaller than the solid particles so the solid stays back, while the liquid passes through.
4. State True or False, with reasons, correcting the false ones: (i) Salt can be separated from salt solution by keeping it under the Sun. (ii) Handpicking should be used only when the quantity of one component is less. (iii) A mixture of puffed rice and rice grains can be separated by threshing. (iv) A mixture of mustard oil and lemon water can be separated by decantation. (v) Sieving is used to separate rice flour and water.
   (i) True — the Sun's heat evaporates the water, leaving salt behind. (ii) True — handpicking is slow, so it suits only small quantities. (iii) False — threshing separates grains from stalks; puffed rice and rice grains differ in weight and size, so winnowing or sieving fits better. (iv) True — oil and water do not mix, and oil floats, so the water can be decanted from below or the oil poured off. (v) False — sieving separates solids of different sizes; rice flour mixed in water is separated by filtration or sedimentation, not sieving.
5. Match: (i) gram flour mixed with black gram, (ii) chalk powder mixed with water, (iii) corn mixed with potatoes, (iv) iron powder mixed with sawdust, (v) oil mixed with water — with handpicking, magnetic separation, decantation, sieving, filtration.
   (i) Sieving — flour passes through, gram stays back. (ii) Filtration — chalk stays on the filter. (iii) Handpicking — corn and potatoes differ in size and shape. (iv) Magnetic separation — the magnet pulls out iron. (v) Decantation — oil floats on water and can be poured off.
6. In what situations would you use decantation instead of filtration?
   When a quick, simple separation is enough and no filter is available, and when the solid has settled well so the clear liquid can be poured off without disturbing it. Filtration is chosen when a clearer liquid is needed.
7. Can you relate nose hair to any separation process? How?
   Yes — filtration. Nose hair acts like a filter, trapping dust and tiny particles from inhaled air while letting air pass through, just as filter paper traps solids while letting liquid pass.
8. Face masks are usually made of what kind of material, and what is their role?
   Masks are made of fine, layered cloth or non-woven fabric with tiny pores. Their role is filtration: they trap dust, droplets and tiny particles while letting air through for breathing.
9. Outline a stepwise procedure to separate a mixture of potatoes, salt and sawdust.
   Step 1: Handpick the potatoes — they are large and differ in size and shape. Step 2: Add water and stir — salt dissolves, sawdust does not. Step 3: Filter — sawdust stays on the filter as residue, salt water passes through as filtrate. Step 4: Evaporate the salt water by heating — water turns to vapour and salt is left behind. All three parts are now separate.

How to use this page: Read the summary, say the Key Terms in your own words, then try the practice set without looking. Use the Questions with Answers to check yourself afterwards. Ask your teacher or parent to check your answers.