1. Pure Substances And Impurities -
ü Unwanted substances present in mixed state with wanted or useful substances are called impurities.
ü The substance of our use which is free from impurities is called pure substance. It usually consist only one type of material.
ü The material that has low level of impurity is called as good quality material whereas the material which has large amount of impurities present is called as poor quality material.
ü Example - Rice and pulses consist of stones. These stones are impurities which must be removed before cooking.
2. Handpicking -
ü Method of handpicking can be used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses.
ü The quantity of such impurities is usually not very large. In such situations, we find that handpicking is a convenient method of separating substances.
3. Threshing -
ü The process that is used to separate grain from stalks etc. is threshing.
ü In this process, the stalks are beaten to free the grain seeds.
4. Winnowing -
ü Method of separating components of a mixture is called winnowing.
ü Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.
5. Sieving -
ü It allows the separation of impurities based on size difference.
ü Larger substances are trapped while smaller pass through.
ü Commonly used to separate flour and bran.
6. Sedimentation And Decantation -
ü When the heavier component in a mixture settles after water is added to it, the process is called sedimentation.
ü When the water (along with the dust) is removed, the process is called decantation.
7. Filtration -
ü The process of separation of impurity from liquid purity is called as filtration.
ü Example - method of separating tea leaves from prepared tea.
8. Evaporation And Condensation -
ü The process of change of liquid into vapor (gas) is called as evaporation.
ü The process of change of vapor (gas) into liquid is called as condensation.
9. Solubility And Saturated Solution -
ü The maximum amount of substance (salt or sugar) that can completely dissolve in water is called as solubility.
ü When more substance (salt or sugar) can not be dissolved into water then solution is called as saturated solution.
NCERT PRACTICE QUESTIONS
1. Why do we need to separate different components of a mixture? Give two examples.
Ans. - When two or more substances are mixed together they form a mixture. Components of a mixture should be separated because some components may not be useful or may spoil the useful component of the mixture.
2. What is winnowing? Where is it used?
Ans. - The method of separating the components from a mixture. In this method, heavier and lighter components of a mixture are separated by wind or by blowing air. This method is used to separate grains from husk.
3. How will you separate husk or dirt particles from a given sample of pulses before cooking?
Ans. - Husk and dirt particles are separated from pulses by handpicking.
4. What is sieving? Where is it used?
Ans. - Sieving is a method in which fine particles are sieved through holes of the sieve while the bigger impurities remain on the sieve. Sieving is used in a flour mill to separate impurities like husk and stones from wheat before grinding it.
5. How will you separate sand and water from their mixture?
Ans. - Sand and water are separated from their mixture by the following steps:
a) The mixture is allowed to stand without any disturbances
b) Now sand settles down
c) Slowly pour the water into another container to obtain sand in the bottom
6. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
Ans. - Yes it is possible to separate sugar mixed with wheat flour by the following method
a) Mix sugar and wheat flour in water
b) Stir the solution to allow sugar to dissolve
c) Now filter the mixture
d) Filtrate contains sugar solution and residue will be wheat flour.
7. How would you obtain clear water from a sample of muddy water?
Ans. - The following process should be carried out to obtain clear water from muddy water
i) Allow muddy water to stand
ii) Mud gets settled down in the water
ii) Slowly pour water to another container
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 ___________.
Ans. - (a) threshing. (b) filtration (c) evaporation (d) decantation.
9. True or false?
(a) A mixture of milk and water can be separated by filtration. ( False)
(b) A mixture of powdered salt and sugar can be separated by the process of winnowing. ( False)
(c) Separation of sugar from tea can be done with filtration. ( False)
(d) Grain and husk can be separated with the process of decantation. ( False)
Junior Science Topic - Separation Of Substances. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 6, CBSE syllabus, chapter 05)
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