Mixtures and methods of separation
When your mother cleans dal, she picks out tiny stones. When tea is poured through a strainer, the tea leaves stay behind. Dal with stones and tea with leaves are mixtures, and each is cleaned by a method that suits it.
A mixture (मिश्रण) has two or more substances, called components (घटक), mixed together. To separate them we use a difference in their properties, such as size, weight, shape, colour or magnetism.
In the figure : In the figure the yellow liquid (X) floats on the blue liquid (water, Y), because it is lighter than water, like oil.
Rule 1: Mixtures are everywhere — Mixtures can be solid + solid, solid + liquid or liquid + liquid.
- Easy : Dal and stones (solid + solid).
- Medium : Muddy water (solid + liquid).
- Exam-type : Oil and water (liquid + liquid): oil floats because it is lighter.
In the figure : The four mixtures are rice and stones, sand and iron nails, muddy water and sea water. Each is separated by using a difference in the properties of its components.
Rule 2: Choose the method by the property — Size → sieving. Weight → winnowing. Magnetism → magnet. Insoluble solid in a liquid → filtration.
- Easy : Iron nails from sand: use a magnet.
- Medium : Light husk from heavy grain: use wind (winnowing).
- Exam-type : Salt dissolved in water: the salt can be got back by evaporation, not by filtration.
Separation uses a difference in properties of the components.
Using filtration for salt dissolved in water. Dissolved salt passes through the filter paper.
Memory clue: Ask first: How do the parts DIFFER?
Spot the difference
| Mixture | Difference | Method |
|---|---|---|
| Dal + stones | Shape, size | Handpicking |
| Sand + iron nails | Magnetism | Magnet |
| Muddy water | Insoluble mud | Filtration |
Practice questions
- 1What is a mixture?
- 2What are the parts of a mixture called?
- 3Why do we separate the components of a mixture?
- 4Why does oil float on water?
- 5Which method separates iron nails from sand?
- 6Is tea with leaves a mixture? Name its components.
- 7A mixture has sugar dissolved in water. Can filtration separate it? Why?
- 8Meena says every mixture can be separated by the same method. Is she right?
Show answers (try them yourself first)
- 1Two or more substances mixed together.
- 2Components
- 3To get a useful or clean substance, like cleaned dal.
- 4Oil is lighter than water.
- 5Using a magnet.
- 6Yes. Tea liquid and tea leaves.
- 7No. Dissolved sugar passes through the filter paper.
- 8No. The method depends on the property that differs.
Winnowing, handpicking and sieving
After harvest, a farmer pours wheat from a height on a windy day and the light husk flies away. A mother runs flour through a sieve to remove lumps. A shopkeeper picks out bad grapes by hand.
Winnowing (उफणणे) uses wind to separate heavy grains from light chaff. Handpicking (वेचणे) picks out a few components by shape and colour. Sieving (चाळणे) separates solids of different sizes with a mesh.
In the figure : In winnowing the wind blows the light husk far away (heap Y), while the heavy grains fall near the tray (heap X).
Rule 1: Winnowing — Heavy grains fall near; light husk is blown far.
- Easy : Winnowing rice at harvest time.
- Medium : It works because husk is lighter than grain.
- Exam-type : On a day with no wind, winnowing does not work well.
Rule 2: Handpicking — Use it when only a few unwanted pieces are present.
- Easy : Taking stones out of dal.
- Medium : Picking bad grapes from a bunch.
- Exam-type : Handpicking is slow for large amounts.
In the figure : In sieving the bigger pieces P stay on the mesh and the smaller sand grains fall through the holes and collect below (Q).
Rule 3: Sieving — Small particles pass through the holes; big ones stay.
- Easy : Wheat flour is sieved to remove bran.
- Medium : Builders sieve sand to remove stones.
- Exam-type : The size of holes decides which particles pass.
Winnowing → difference in weight. Sieving → difference in size. Handpicking → shape and colour.
Sieving a mixture whose particles are all of the same size. Sieving needs a size difference.
Memory clue: Wind – Weight; Sieve – Size; Hand – shape and colour.
Spot the difference
| Method | Property used | Example |
|---|---|---|
| Winnowing | Weight | Wheat and husk |
| Sieving | Size | Flour and bran |
| Handpicking | Shape, colour | Stones in dal |
Practice questions
- 1What is winnowing?
- 2What is sieving?
- 3When is handpicking used?
- 4Which property does winnowing use?
- 5Which method removes stones from sand?
- 6Why does the husk fly farther than the grain?
- 7Why does flour pass through a sieve but bran does not?
- 8Rice is mixed with a lot of sand. Is handpicking a good choice? Why?
Show answers (try them yourself first)
- 1Separating heavy grains from light chaff using wind.
- 2Separating solids of different sizes using a mesh.
- 3When only a few unwanted components are present.
- 4Difference in weight.
- 5Sieving
- 6It is lighter.
- 7Flour particles are smaller than the holes; bran pieces are bigger.
- 8No. Sand is too much and too small to pick by hand; sieving is better.
Filtration, sedimentation and decantation
Pond water after rain is muddy. If you leave it undisturbed in a bucket, the mud sinks and the water above becomes clear. You can then pour off the clear water slowly. Or you can pour it through a cloth.
Filtration (गाळणे) separates an insoluble solid from a liquid with a strainer or filter paper. Sedimentation (गाळ बसवणे) lets heavy insoluble particles settle. Decantation (निवळी ओतणे) is pouring off the clear liquid. Alum makes soil settle faster.
In the figure : In filtration the muddy water is poured through the filter paper in the funnel (A). The solid stays on the paper and the clear liquid collects in the beaker (B).
Rule 1: Filtration — Insoluble solid stays on the paper; liquid passes through.
- Easy : Tea strainer holds tea leaves back.
- Medium : A coffee filter holds back coffee grounds.
- Exam-type : A filter cannot remove dissolved salt.
In the figure : In sedimentation the heavy mud particles settle at the bottom of the jar with time, and the water above becomes clear.
Rule 2: Sedimentation — Heavy particles settle; alum makes this faster.
- Easy : Muddy pond water in a bucket becomes clear after some time.
- Medium : Adding a piece of alum makes the mud settle faster.
- Exam-type : Sedimentation is slow; do not shake the jar.
In the figure : In decantation the clear liquid is poured off slowly from jar P into beaker Q, while the settled mud stays behind in the jar.
Rule 3: Decantation — Pour off slowly so the settled solid stays behind.
- Easy : Pouring clear water off muddy sediment.
- Medium : Sedimentation and then decantation are used together.
- Exam-type : For cleaner water, decant first, then filter.
Filtration, sedimentation and decantation all separate insoluble solids from liquids.
Thinking filtration separates anything dissolved. It only removes insoluble solids.
Memory clue: Sit → Pour → Strain (sediment, decant, filter).
Spot the difference
| Method | What happens | Needs |
|---|---|---|
| Sedimentation | Heavy particles settle | Time, alum |
| Decantation | Clear liquid poured off | Slow pouring |
| Filtration | Solid stays on paper | Funnel, filter paper |
Practice questions
- 1What is filtration?
- 2What is sedimentation?
- 3What is decantation?
- 4What does alum do to muddy water?
- 5Name two things used in filtration.
- 6What stays on the filter paper?
- 7Write the order to clean muddy water well: filtration, sedimentation, decantation.
- 8Raju shakes the jar while pouring to decant. What is wrong?
Show answers (try them yourself first)
- 1Separating an insoluble solid from a liquid using a strainer or filter paper.
- 2Heavy insoluble particles settling at the bottom.
- 3Pouring off the clear liquid slowly.
- 4It makes the mud settle faster.
- 5Funnel and filter paper.
- 6The insoluble solid.
- 7Sedimentation → decantation → filtration.
- 8The settled mud rises again and gets poured off with the water.
Churning and evaporation
Cream from curd is stirred in a churner and a lump of butter rises above the buttermilk. Wet clothes dry in the sun and water disappears from them. A salt farm lets sea water dry in the sun to leave salt behind.
Churning (घुसळणे) separates butter, which floats, from buttermilk. Evaporation (बाष्पीभवन) is the change of a liquid into vapour due to heat. It is used to get salt from sea water.
In the figure : In evaporation the water of a salt solution turns into vapour and the salt is left in the dish. The dish over a flame (A) dries up faster than the dish in the sun (B).
Rule 1: Churning — Light butter floats on heavier buttermilk.
- Easy : Butter from cream.
- Medium : Buttermilk stays below; butter is collected from the top.
- Exam-type : Churning uses the difference in weight.
Rule 2: Evaporation — Heat turns the water to vapour; the dissolved solid is left behind.
- Easy : Salt from sea water in salt pans.
- Medium : Heating on a flame is faster than drying in the sun.
- Exam-type : Dissolved sugar or salt can be recovered, but not by filtration.
Churning separates butter from buttermilk. Evaporation separates a dissolved solid from its liquid.
Thinking the salt also goes away with the water. Only water changes to vapour; salt stays.
Memory clue: Vapour leaves, solid stays.
Spot the difference
| Method | Used for | Example |
|---|---|---|
| Churning | Butter from buttermilk | Cream |
| Evaporation | Dissolved solid from liquid | Salt from sea water |
| Speed | Faster with heat | Slow in shade |
Practice questions
- 1What is churning?
- 2What is evaporation?
- 3How is salt obtained from sea water?
- 4What floats on buttermilk?
- 5Which dries faster: a dish over a flame or in the sun?
- 6What is left in the dish after the water evaporates from salt solution?
- 7Why do wet clothes dry faster on a hot sunny day?
- 8Sita says salt goes into the air with water vapour. Correct her.
Show answers (try them yourself first)
- 1Separating butter from buttermilk by stirring.
- 2Change of a liquid into vapour due to heat.
- 3By evaporation in salt pans.
- 4Butter
- 5The dish over a flame.
- 6Salt
- 7Heat makes water evaporate faster.
- 8Only water changes to vapour. Salt is left behind.
Magnetic separation and applications
In a scrap yard a crane with a big magnet lifts old iron pieces from a pile of mixed waste. The plastic, glass and wood stay behind. Magnetic separation uses the property of magnetism.
Iron, cobalt and nickel are attracted by a magnet. Magnetic separation (चुंबकीय पृथक्करण) uses a magnet to remove such materials from a mixture, for example from garbage.
In the figure : A magnet attracts only the iron nails (A). The plastic beads, sand and wooden sticks are not magnetic, so they are not attracted.
Rule 1: Magnetic materials — Iron, cobalt and nickel are attracted. Plastic, wood, glass and sand are not.
- Easy : An iron pin sticks to a magnet.
- Medium : A plastic button does not stick.
- Exam-type : A steel paper clip sticks, because steel is mostly iron (stainless steel usually does not stick).
Rule 2: Uses — Magnetic separation removes iron from garbage and from grain or sand at factories.
- Easy : Scrap yards lift iron with big magnets.
- Medium : Dr. Uddhab Bharali of Assam invented over 160 machines.
- Exam-type : Mixtures with iron and sand: use a magnet first, then sieve.
Magnetic separation works only when one component is magnetic.
Using a magnet on salt and sand. Neither is magnetic.
Memory clue: Magnet attracts I-C-N: Iron, Cobalt, Nickel.
Spot the difference
| Material | Attracted? |
|---|---|
| Iron nail | Yes |
| Plastic bead | No |
| Sand | No |
Practice questions
- 1Name three materials attracted by a magnet.
- 2What is magnetic separation?
- 3Is a plastic bead attracted by a magnet?
- 4Where is magnetic separation used?
- 5Who invented over 160 machines?
- 6Can a magnet separate salt from sand? Why?
- 7A mixture has iron nails, sand and wooden sticks. Suggest the steps to separate all three.
- 8A steel paper clip sticks to a magnet. Why?
Show answers (try them yourself first)
- 1Iron, cobalt and nickel.
- 2Using a magnet to remove magnetic materials from a mixture.
- 3No
- 4In scrap yards and to remove iron from garbage.
- 5Dr. Uddhab Bharali
- 6No. Neither is magnetic.
- 7Magnet takes the nails; sieving separates sticks from sand.
- 8Steel is mostly iron, which is magnetic.
Quick revision
- Winnowing (wind), sieving (size), filtration (insoluble solid), sedimentation and decantation, evaporation (salt), magnet (iron).
Quick revision
In the app you can move this figure with your finger.
Open in the app