Introduction
Before trying to attempt to answer the NCERT exercise questions, you should have a thorough understanding of class 6 Science chapter 3 i.e. ‘Separation of Substances’.
If you haven’t understood the chapter yet, then worry not you can go through it easily and develop a crystal clear understanding of various concepts from our notes whose link has been provided below
NCERT Exercise Questions & Answers
Que. 1 Why do we need to separate different components of a mixture? Give two
examples.
Ans. 1 When two or more than two different substances are mixed together they form a mixture. Not all the components of a mixture are of our use. So sometimes we need to separate the useful component(s) from the non-useful or non-required or even harmful components.
Examples: I) Separating grains from the stalk.
II) Separating tea leaves from the liquid tea.
III) Separating rotten bananas from the ripened ones from a bunch.
Que. 2 What is winnowing? Where is it used?
Ans. 2 Winnowing is a method of separation that is used to separate the similar-sized heavier and lighter components of a mixture with the help of wind or blowing air.
Winnowing is used by farmers to separate lighter husk particles from the heavier grain seeds.
Que. 3 How will you separate husk or dirt particles from a given sample of pulses before
cooking?
Ans. 3 If the number of husk particles is less, then we can separate them out by handpicking method of separation.
But, if the number of husk particles is more, then we can separate them from the pulses by winnowing.
We can separate dirt particles either by winnowing or by sedimentation & decantation.
Que. 4 What is sieving? Where is it used?
Ans. 4 Sieving is a method of separation of components of a mixture that has differences in size.
A mixture is separated by using a tool (sieve or mesh). The mixture is poured onto the sieve and the
finer component sieves out and the larger components remain on the sieve.
Sieving can be used: I) For Separating wheat flour from bran and other impurities.
II) Before grounding the wheat in flour mills, impurities like stones and husks are separated from grains using a sieve.
III) For construction purposes, sieving is used to separate pebbles and stones from the sand.
Que. 5 How will you separate sand and water from their mixture?
Ans. 5 We can employ two different ways to separate sand and water from their mixture.
The first one is based on sedimentation & decantation
- Put the mixture into a beaker.
- Let it stand until all the sand settles down.
- Decant the water into another beaker to obtain sand at the bottom of the beaker.
The second one is based on vaporisation & condensation
- Pour the mixture into a beaker.
- Put the beaker onto a hot plate or heater and start heating.
- Take a metal plate and put some ice on it.
- Keep the metal plate near the top of the beaker that is being heated and tilt it towards a new beaker that is being used to collect the condensed water vapour.
- Boil off all the water from the mixture and you will be left with sand into that beaker and the water is collected into another beaker with the help of condensation.
Que. 6 Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
Ans. 6 We can separate sugar from the sugar and wheat flour mixture by sieving. As there is a difference between the size of sugar granules or particles and wheat flour particles. With sugar particles being the larger in size will remain on the sieve and wheat flour will sieve out.
Que. 7 How would you obtain clear water from a sample of muddy water?
Ans. 7 We can obtain clear water from a sample of muddy water by employing this integrated approach of separation involving sedimentation, decantation and filtration.
Here is the procedure to be followed for the separation of clear water from a sample of muddy water.
- Collect the muddy water sample in a beaker or other vessel.
- Allow it to stand till all the mud sediments.
- Then decant the water into another beaker.
- Now, once we have collected water which is much less turbid.
- We will now filter it through a muslin cloth or a very fine cloth to remove most of the dirt or mud.
- Now the water that we have collected after filtering through the muslin cloth will be almost free of dirt.
- But if you still want to filter it and want to remove most of the dirt then filter it through the filter paper.
- Now clear water has been obtained from the sample of muddy water.
Que. 8 Fill up the blanks
(a) The method of separating the seeds of paddy from its stalks is called—–.
(b) When milk, cooled after boiling, is poured onto a piece of cloth the cream
(malai) is left behind on it. This process of separating cream from milk is an
example of ——-.
(c) Salt is obtained from seawater by the process of ——.
(d) Impurities settled at the bottom when muddy water was kept overnight in a
bucket. The clear water was then poured off from the top. The process of
separation used in this example is called ——.
Ans. 8 (a) The method of separating the seeds of paddy from its stalks is called threshing.
(b) When milk, cooled after boiling, is poured onto a piece of cloth the cream
(malai) is left behind on it. This process of separating cream from milk is an
example of filtration.
(c) Salt is obtained from seawater by the process of evaporation.
(d) Impurities settled at the bottom when muddy water was kept overnight in a
bucket. The clear water was then poured off from the top. The process of
separation used in this example is called sedimentation and decantation.
Que. 9 True or false?
(a) A mixture of milk and water can be separated by filtration.
(b) A mixture of powdered salt and sugar can be separated by the process of
winnowing.
(c) Separation of sugar from tea can be done with filtration.
(d) Grain and husk can be separated with the process of decantation.
Ans. 9 (a) False. A mixture of water and milk cannot be separated by the filtration method.
(b) False. A mixture of salt and sugar cannot be separated by the winnowing method.
(c) False. As sugar cannot be separated from tea by filtration method.
(d) False. As grain and husk cannot be separated by decantation method.
Que. 10 Lemonade is prepared by mixing lemon juice and sugar in water. You wish to
add ice to cool it. Should you add ice to the lemonade before or after dissolving
sugar? In which case would it be possible to dissolve more sugar?
Ans. 10 Ice should be added after dissolving sugar as we know with a decrease in temperature the solubility of solute (sugar) in solvent (water) decreases. So more sugar will dissolve in normal water than in icy cold water.
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