Separation of Substances (part -1) class 6


Separation of Substances

Q.1. What do we mean by the term 'mixture'? Give some instances from real life when we notice a substance being separated from a mixture of materials.
Ans. A mixture is made up of two or more pure substances. The pure substances  which are present in mixture are called components of a mixtures.
There are many instances from real life when we notice a substance being separated from a mixture of materials. For example:
  • Tea leaves are separated from the liquid with a strainer, while preparing tea.
  • Grain is separated from stalks, while harvesting.
  • Milk or curd is churned to separate the butter.
  • we gin cotton to separate its seeds from the fibre.
  • Separating green chillies from food if we don’t want to eat them.
Q.2.  Why do we separate substances?
Ans.  Before we use a substance,
  • We need to separate harmful substances that may be mixed with it.
  • We need to separate non-useful substances that may be mixed with it.
  • Sometimes, we separate even useful components if we need to use them separately. 
Q.3. Match the following:
                                 
Ans. (1)-(c)-(ii)
       (2)-(a)-(iii)
       (3)-(b)-(i)

Q.4. What basic idea should we keep in mind for separation of substances?
Ans. To separate a mixture, we have to use some property that one component of mixture has but other component does not have.

 Q.5. Why can’t we use same method for all mixtures?
Ans.  We can't use same method for all mixtures because

  • The substances to be separated may be particles of different sizes or materials.
  • These may be solids, liquids or even gases.

Q.6. Write a short note on each:
    Handpicking, Threshing, winnowing, sieving and Magnetic separation.
Ans. 
(a) Handpicking

  • Hand picking is a method of separation of solid which involves picking out substances by hand and separating them from others. 
  • Hand picking can be used when the components to be separated are:
    •  big enough to handle
    • different in size, colour and shape
    • in a small quantity in the mixture
  • For example, Removal of the pieces of dirt, stone, and husk from wheat, rice or pulses is done by handpicking.
(b) Threshing
  • Threshing is the process that is used to separate by beating the mixture.
  • For example,  loosening the edible part of grain from the chaff to which it is attached by beating the pile of stalks on a large stone.
(c)Winnowing
  • Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.
  • The lighter particles are carried away by the wind while heavier particles get separated and form a heap near the platform for winnowing.
  • For example, This method is commonly used by farmers to separate lighter husk particles from heavier seeds of grain.
(d) Sieving
  • Sieving is used when components of a mixture have different sizes.
  • Sieving allows the fine particles to pass through the holes of the sieve while the bigger impurities remain on the sieve.
  • For example, Pebbles and stones are removed from sand by sieving.

(e) Magnetic separation
  • Removing out the magnetic components from a mixture by a magnet is called magnetic separation.
  • For example, Picking up pieces of iron from waste.




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