Handpicking, threshing and winnowing
Before cooking, we pick stones out of dal; after harvest, farmers beat the crop to free the grain and let the wind blow away the husk.
A mixture has two or more things mixed together. Handpicking removes visible pieces by hand. Threshing frees grains from the stalks. Winnowing uses wind to blow away the light husk while the heavy grain falls down.
In the figure: Wind carries the light husk away; the heavy grain falls down.
Rule 1: Handpicking — Use it when the pieces are big enough to see and few in number.
- Easy: Picking stones from rice or dal.
- Medium: Removing bad fruit from a basket.
- Exam-type: It is too slow for large amounts.
Rule 2: Threshing and winnowing — First free the grain, then blow away the husk.
- Easy: Threshing: beating the harvested crop to release grains.
- Medium: Winnowing works because husk is lighter than grain.
- Exam-type: It needs a breeze; on a still day it fails.
Choose the method by what is different between the parts: size, weight or looks.
Using winnowing on a windless day or for heavy impurities.
"Pick the visible, beat to free, wind for light."
Practice questions
- 1Which method uses wind or blowing air?
- 2Picking out unwanted particles by hand from a mixture is called —
- 3Handpicking is done on the basis of differences in —
- 4Nani removes small stones from grains so that the grains are —
- 5Traditionally, a farmer uses a soop for winnowing. A soop is a —
- 6When roasted peanuts are rubbed and blown over, the component blown away is —
- 7Handpicking is convenient when the particles to be removed are —
- 8Malli separating whole black peppers from the pulao is an example of —
Show answers (try them yourself first)
- 1Winnowing
- 2handpicking
- 3size, colour and shape of particles
- 4fit for cooking
- 5bamboo tray
- 6the removed peanut skins
- 7present in small quantities and easily picked by hand
- 8handpicking
Sieving, churning and magnetic separation
Mother sifts flour to remove lumps, churns curd to take out butter, and a magnet picks pins out of a heap of sand.
Sieving uses a sieve with holes: small pieces pass through, big ones stay. Churning spins a liquid quickly so the lighter part, like butter, separates and rises. Magnetic separation uses a magnet to pull out iron from a mixture.
In the figure: A sieve separates by size; a magnet pulls only iron.
Rule 1: Sieving — The holes must be smaller than the big pieces.
- Easy: Sifting flour and sand at a building site.
- Medium: Different sieves have different hole sizes.
- Exam-type: Tea strainer is a small sieve.
Rule 2: Churning and magnet — Match the method to the property.
- Easy: Churning separates butter from curd or cream.
- Medium: A magnet picks iron, nickel and cobalt only.
- Exam-type: Used in scrap yards and to remove iron filings.
A magnet cannot lift sand, plastic or wood; try it only for iron.
Thinking a magnet attracts every metal.
"Holes by size, spin for light, magnet for iron."
Practice questions
- 1What is left behind after butter separates during churning?
- 2In sieving, the fine flour particles —
- 3Bigger particles such as bran and small stones —
- 4At construction sites, sieves are used to separate —
- 5A common example of a magnetic substance is —
- 6Sieving is used when the components of a solid–solid mixture have —
- 7Sieving will not work if the holes of the sieve are —
- 8To remove bran from wheat flour, Mami uses —
Show answers (try them yourself first)
- 1Buttermilk (chhach)
- 2pass through the holes of the sieve
- 3remain on the sieve
- 4pebbles and stones from sand
- 5iron
- 6different sizes
- 7larger than all the particles of the mixture
- 8a sieve
Separating salt by evaporation
Seawater is let into shallow pans on the coast; after some days the water is gone and white salt remains.
When salty water is left in the sun, the water turns into vapour by evaporation, but the salt cannot evaporate and stays behind as crystals. This separates a dissolved solid from its liquid. The process is faster in a wide shallow pan with sun and wind.
In the figure: Water leaves as vapour; salt crystals remain in the pan.
Rule 1: How it works — Only the liquid evaporates, not the solid.
- Easy: Heat and wind speed up evaporation.
- Medium: A wide pan gives more surface and dries faster.
- Exam-type: The salt left is solid crystals you can collect.
Rule 2: Where it is used — Works for any dissolved solid in a liquid.
- Easy: Salt pans on the sea coast.
- Medium: Making salt from a salty solution at home in a dish.
- Exam-type: It does not recover the water; condensation would be needed.
Never boil a hot salt solution carelessly; let the sun do the work, or ask an adult.
Thinking that salt also evaporates with the water.
"Water goes, salt stays."
Practice questions
- 1Which process helps to get water back from water vapour?
- 2Common salt is obtained from —
- 3Seawater is a mixture of —
- 4Common salt is obtained from the solid left in the pits by —
- 5In Activity 9.3, the salt solution is heated in a —
- 6Drying herbs in the shade helps —
- 7To obtain salt, seawater is kept in —
- 8When the water in the pits evaporates completely, what is left behind?
Show answers (try them yourself first)
- 1Condensation
- 2seawater
- 3salts and other substances dissolved in water
- 4further purification
- 5china dish
- 6evaporation of excess water
- 7shallow pits exposed to sunlight and air
- 8A solid mixture from which salt is purified
Sedimentation, decantation and filtration
Muddy rainwater left in a bucket becomes clear on top after a while, and we can then pour off the clear water or pass it through a cloth.
Sedimentation lets heavy insoluble particles settle at the bottom. Decantation carefully pours off the clear liquid on top. Filtration passes the liquid through a filter paper or cloth that holds back fine particles. Together they clear muddy water.
In the figure: Settle, pour the top water off, then filter what is left.
Rule 1: Settle and pour — Be patient and do not shake the container.
- Easy: Heavier mud sinks first.
- Medium: Pouring slowly keeps the sediment behind.
- Exam-type: Used for separating water and oil too.
Rule 2: Filtration — Fine particles need a filter.
- Easy: Filter paper, cloth or a tea strainer works.
- Medium: The liquid that passes is the filtrate.
- Exam-type: A filter cannot remove dissolved salt.
Filtering clears insoluble dirt but does not make water safe to drink.
Expecting a filter to remove dissolved salt or sugar.
"Settle, pour, filter."
Practice questions
- 1The settling of a heavier insoluble component at the bottom of a liquid is called —
- 2Removing the liquid by tilting the vessel gently, leaving the settled solid, is called —
- 3Filtration is used to separate —
- 4In filtration, the clear liquid collected in the flask is the —
- 5A fisherman's net draining water through the mesh is similar to —
- 6Decantation does not completely separate the tea leaves because —
- 7Pouring tea through a strainer to separate the leaves is —
- 8A piece of cloth can act as a filter because it has —
Show answers (try them yourself first)
- 1sedimentation
- 2decantation
- 3insoluble solid components from a liquid
- 4filtrate
- 5filtration
- 6a few tea leaves can still come with the tea
- 7filtration
- 8very small pores between woven threads
Choosing methods and everyday uses
A cook washes rice (settle and pour), sifts flour, and removes tea leaves with a strainer: each job uses a different method.
Pick the method from the difference in properties: size (sieving), weight (winnowing), magnetism (magnet), solubility (filtration, evaporation). A mixture with several parts needs several steps, each removing one part.
In the figure: Iron + sand + salt: magnet, then water and filter, then evaporate.
Rule 1: Match property to method — Ask what differs between the parts.
- Easy: Size differs: sieving.
- Medium: Iron present: magnet.
- Exam-type: Dissolved solid: evaporation.
Rule 2: Order of steps — Remove the part that is easiest first.
- Easy: Take iron out with a magnet before adding water.
- Medium: Add water, then filter out the sand.
- Exam-type: Evaporate the clear salty water last for the salt.
Write the steps in order and name the property each step uses.
Choosing evaporation before removing sand, which leaves the salt dirty.
"Different property, different method, in order."
Practice questions
- 1For a mixture of potatoes, salt and sawdust, which step is best done first?
- 2Which method separates grains from harvested stalks?
- 3Why do we separate substances from a mixture?
- 4Sorting sawdust and iron nails from building material is done by —
- 5Separating pebbles from sand is done by —
- 6Churning curd to obtain butter separates —
- 7Nasal hair helps by —
- 8Picking marigold flowers from a heap of flowers to make a garland is —
Show answers (try them yourself first)
- 1Handpick the potatoes
- 2Threshing
- 3To remove unwanted components or to separate two useful components
- 4magnetic separation
- 5sieving
- 6two useful components, butter and buttermilk
- 7trapping dust from the air we breathe, like a filter
- 8handpicking
Choosing methods and everyday uses
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