Saturday, May 12, 2012

6th Science : Cleaning of food or Separation of Substances solved question

Q. What is substance?
Ans: A kind of matter that cannot be separated by physical methods.
Q. What is pure substance?
Ans: Clean and diseases free substance are called pure elements.
Q. what is matter?
Ans: Everything around us having mass and volume is called matter. it is of three types element compound and mixture.
Q. What is compound?
Ans: Ans: The substance containing two or more types of substance mixed together in fix ratio is called salt, sugar and water
Q. What is mixture?
Ans: The substance containing two or more types of substance mixed together in any ratio is called air , food  grain, milk, sea water. A mixture can be separated by physical methods.
Q. Give two properties of mixtures.
Ans. (i) The ratio of their constituents is not fixed.
(ii) Mixtures do not have definite melting point or boiling point.
Q. Why we need to separate mixture?
Ans:  The following are the reasons for the separation:
(i) to remove the undesirable constituents from mixture. (ii) To obtain desirable substances from mixture.  (iii) To obtain highly pure substance.
Q. What is Chaff or husk?
Ans: the debris arising from agriculture processing of food grain like maize, rice wheat is called chaff.
Q. Differentiate between hand picking & winnowing.
Ans. Hand picking: the process of cleaning mixture by picking out with hand.
It is used when the constituents of the mixture are big in size & visibly differently .For example: separating stones from rice.
Winnowing: The process of cleaning mixture like husk from grain with the help of wind which blow lighter husk.
It is used when one of the constituents is lighter and  the other is heavier, For example:  shaff from grain.
Q. Define sieving
Ans: The process of separating fine lighter particles from larger particles using sieve. Eg husk, gravel, dust ,tea leaves etc .
Size of the holes of sieve or mash depends on the size of particles separated.
if the solid mixture is stirred or shaken on a mesh. Particles smaller than the holes of the mesh fall & the bigger ones remain on the mesh.
Q. what is sedimentation and decantation?
Ans: The process of separating heavier insoluble solid particles mixed in liquid. For separating we left mixture u disturbed for some time.  The heavier particles settle down at bottom is called sediment.
The method of collecting clear liquid from sediment is called decantation.

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