CLASS 6 SCIENCE · CHAPTER 9 · STUDY NOTES
Methods of Separation in Everyday Life
Choose methods by properties, follow each component and combine steps when needed.
01 / EXPLORE & UNDERSTAND
Choose a method from the difference
Separation is useful when we want one or more parts of a mixture apart.
1. Say what you want to keep
We may remove unwanted stones from grain, or collect two useful materials separately. “Unwanted” depends on the task; it is not a permanent property of the substance.
2. Find a property that differs
Size, response to wind, solubility and magnetic attraction can help. A method works because of a useful difference between the components, not because its name sounds suitable.
Your turn
Question
Why might two useful substances still need separating?
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02 / EXPLORE & UNDERSTAND
Handpick what you can recognise and grasp
Handpicking suits small amounts of easily recognised pieces.
1. Use visible differences
A few stones in a bowl of grain differ in shape, size or colour. You can pick them out individually. The task becomes slow when there are many tiny pieces.
2. Know its limits
You cannot handpick dissolved salt from water. The method needs pieces large enough to identify and grasp. Use safe classroom materials, not sharp fragments or unknown waste.
Your turn
Question
Why is handpicking a poor way to separate a spoon of fine sand mixed through flour?
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03 / EXPLORE & UNDERSTAND
First free the grain from the stalk
Grains attached to stalks need a different step from grains already mixed with loose husk.
1. Identify what is attached
Threshing loosens and removes grains from the harvested stalks. It does not automatically produce completely clean grain. Loose husk can remain mixed with it.
2. Separate the jobs inside a machine
A farm machine can perform threshing and further cleaning together. Even when one machine does both, freeing grain and separating loose husk remain different jobs.
Your turn
Question
After threshing, grain and loose husk are together. Why is more separation still needed?
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04 / EXPLORE & UNDERSTAND
Let moving air separate husk and grain
Husk and grain respond differently when falling through moving air.
Trace the two paths from the tray
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1. Follow the two landing places
When the mixture falls from a tray, the light husk is carried farther sideways by air. The heavier grain falls nearer the tray. The collected piles are in different places.
2. Check the air and the mixture
Without sufficient moving air, the separation is poor. This method is useful for suitable dry mixtures; it is not a way to remove dissolved substances from water. The particles’ shape and response to air matter as well as mass.
Your turn
Question
Why do the two piles not form well when a dry grain–husk mixture is dropped in still air?
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05 / EXPLORE & UNDERSTAND
Match the holes to the particle sizes
A sieve separates by size, so choosing its holes matters.
The fine part passes through
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1. Compare three sizes
For coarse pieces mixed with finer particles, choose holes larger than the fine particles but smaller than the coarse pieces. The fine portion passes through; the coarse portion stays.
2. Explain a failed separation
If the holes are larger than both components, both pass. If smaller than both, both remain. Similar-sized components cannot be separated well by size alone.
Your turn
Question
A sieve lets both sand and the unwanted small pebbles through. What is wrong with the choice?
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06 / EXPLORE & UNDERSTAND
Recover the dissolved solid
Filtering salt water through ordinary paper does not remove the dissolved salt. Evaporation can leave it behind.
Evaporation over a wide surface
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1. Track what leaves and what remains
As water evaporates from salt solution, salt remains. In salt works, shallow ponds expose seawater to sun and air; further purification is needed to obtain common salt from the remaining mixture.
2. Collect water only if you trap and condense vapour
Open evaporation loses water to the air. To recover it too, vapour must be collected and cooled into liquid. Heating apparatus is a teacher demonstration, not a home experiment for children.
Your turn
Question
A learner evaporates a salt solution in an open dish and says both salt and water were collected. What is incorrect?
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07 / EXPLORE & UNDERSTAND
Let particles settle, then pour carefully
Sedimentation and decantation are two linked actions, not one name for the same thing.
1. Wait without stirring
Heavier insoluble particles can settle at the bottom when a mixture is left still. This settled material is sediment. Very fine particles may take longer or remain suspended.
2. Pour without disturbing the bottom
Gently pour the clearer liquid into another vessel, leaving sediment behind. Some particles may still pass over. Decantation can also separate a layer of oil from water, but needs care to avoid mixing the layers again.
Your turn
Question
A jar is shaken just before pouring off the clear water. Why might decantation fail?
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08 / EXPLORE & UNDERSTAND
Follow residue and filtrate
A filter’s pores must be small enough to trap the particles we want to remove.
Keep track of both outputs
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1. Connect pore size to the result
A tea strainer holds leaves, but smaller muddy particles may pass through its mesh. Fine filter paper can retain smaller particles. In the book setup, the paper lines a funnel and the liquid is collected below.
2. Clear does not mean safe or pure
Ordinary filtration does not remove dissolved salt, and not every filter removes microbes. Never drink a classroom filtrate just because it looks clear. Preventing pollution is better than assuming a simple filter can fix everything.
Your turn
Question
Muddy salt water is passed through ordinary filter paper. Where do mud and dissolved salt go?
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09 / EXPLORE & UNDERSTAND
Use a different property when size is not enough
Churning and magnetic separation solve different kinds of separation problems.
A magnet selects iron from sawdust
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1. Churning collects butter
Churning curd helps fat collect into butter, which is separated from the remaining buttermilk. This is not sieving grains or evaporating all the liquid. Different food mixtures need appropriate processes.
2. A magnet selects magnetic material
A magnet can collect iron pieces from dry sawdust because iron is attracted and wood is not strongly attracted. A magnet does not collect every metal: aluminium and copper do not behave like iron in this classroom test.
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Question
Would a magnet reliably remove copper pieces from sawdust in the same way as iron pieces?
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10 / EXPLORE & UNDERSTAND
Plan the order for a mixed mixture
More components may need several methods in sequence.
1. Remove what a magnet can select
Imagine a dry classroom mixture of iron washers, sand and salt. Use a magnet first to lift out the iron washers. Explain why this step works: the components differ in magnetic attraction.
2. Use solubility, then size, then evaporation
Add enough water to dissolve the salt. Filter to retain sand while salt solution passes through. Evaporating the water can recover salt; the teacher handles any heating. Track each component after every step so none is accidentally discarded.
Your turn
Question
After filtering the sand–salt mixture, a learner throws away the filtrate. Which wanted component is lost?
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Sign inNew here? Sign up freeCHAPTER RECAP
Take these ideas with you
- Choose a method by a difference between components.
- Threshing frees grain from stalks; winnowing separates loose husk using air.
- Sieving uses different particle sizes and suitable openings.
- Sedimentation settles solids; decantation pours off a layer.
- Filtration retains residue; filtrate passes through. Dissolved salt can pass too.
- Evaporation, churning and magnetic separation each rely on different behaviour.
Use your understanding in a new situation
Question
Why is a sieve ineffective for two kinds of dry grains with almost the same size?
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Sign inNew here? Sign up freeQuestion
After filtering a salty muddy sample, can you call the clear filtrate pure water? Explain.
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