Goa Board Class 6 Solutions for Science – Separation of Substances (English Medium)
Page No. 44:
Question 1:
Why do we need to separate different components of a mixture? Give two examples?
Solution:
We need to separate different components of a mixture:
a.To separate two different but useful components.
b.To remove non useful components.
c.To remove impurities or harmful components.
Examples:
i.Through winnowing, we can separate grain from husk.
ii.Through evaporation, salt can be obtained from sea water.
Concept insight: Mixtures are separated to obtain individual components.
Question 2:
What is winnowing? Where is it used?
Solution:
Winnowing is a physical method of separation. It is used to separate heavier and lighter components of a mixture by wind. It is used by farmers to separate lighter husk particles from heavier seed grains.
Concept insight: When a mixture is made to fall down from a height due to wind, lighter particles fall far away and heavier particles fall near the winnowing platform. It is used to separate husk from wheat grains.
Question 3:
How will you separate husk or dirt particles from a given sample of pulses before cooking?
Solution:
To separate husk, winnowing is done. To separate dirt from pulses, we will add water to them. Dirt will get dissolved in water, husk being lighter will float on water and pulse grain will settle down.
Then, water with impurities can be removed by decantation.
Concept insight: Husk being light in weight can removed by winnowing and dust is soluble in water so, it can be separated by decantation.
Question 4:
What is sieving? Where is it used?
Solution:
Sieving is a process through which dirt impurities and bran present in grains and pulses are removed with the help of sieve. It is used at home, in flour mills and at construction sites.
Concept insight: Stones and bran cannot be separated by sedimentation or winnowing so, they are separated by sieving.
Question 5:
How will you separate sand and water from their mixture?
Solution:
We can separate a mixture of sand and water by:
i.Sedimentation and decantation.
ii.Filtration.
Concept insight: Sand is insoluble in water and being heavy, it settles down in the beaker thus, it can be separated by sedimentation and decantation. Also sand particles are big so they do not pass through a cotton cloth hence, sand and water can also be separated by filtration.
Question 6:
Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
Solution:
Yes. It is possible to separate a mixture of sugar and wheat flour. This can be done by the process of sieving. If the mixture of sugar and wheat flour is allowed to pass through a sieve, then the fine wheat flour particles would pass through the sieve, the sugar particles would be retained by the sieve.
Question 7:
How would you obtain clear water from a sample of muddy water?
Solution:
Clear water can be obtained from a sample of muddy water by the method of filtration. In this method, the sample of muddy water is passed through a cloth having fine pores or through a filter paper. Clear water will pass through the filtering medium, leaving behind the mud.
Question 8:
Fill up the blanks:
(a) The method of separating 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 ___________.
Solution:
(a) Threshing.
Concept insight: It is very difficult to take out each grain from the stalks so stalks are beaten to free the seeds. This process is called threshing.
(b) Filtration.
Concept insight: Cream particles being bigger do not pass through cloth.
(c) Evaporation.
Concept insight: Conversion of water into water vapour below its boiling point is called evaporation.
(d) Sedimentation and Decantation
Concept insight: Soil particles being heavy settle at the bottom of the container. After that, clear liquid can be removed by decantation.
Question 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.
Solution:
(a) False.
Concept insight: No, because both are liquids.
(b) False.
Concept insight: Winnowing is used to separate a mixture of solids of which one is light weight and other is heavy weight.
(c) False.
Concept insight: No, filtration can not be used to separate dissolved substances.
(d) False.
Concept insight: Decantation is used to separate a mixture of insoluble solid in liquid.
Page No. 45:
Question 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?
Solution:
We should add ice after dissolving sugar because the dissolving power of water decreases with decrease in temperature. So, if we add ice before dissolving sugar, less amount of sugar will get dissolved.
Concept insight: Dissolving power of water increases with temperature and vice versa.