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b) Separating oil from water decantation
c) Chalk from water filtration
d) Bran from flour sieving
e) Pulses from rice hand picking
Q7. Why filtration is preferred over decantation?
Ans. Sometimes in decantation the liquid is not completely
separated from an insoluble liquid then we
apply the method of decantation.
Q8. Define supernatant liquid.
Ans. The liquid above the sediment is known as supernatant
liquid.
Q9. Why do we employ the method of loading sometimes after
sedimentation & decantation?
Ans. Loading helps sedimentation. Sometimes very fine solid
particles do not sink to the bottom, they
remain suspended in water so these fine particles can be
separated from loading.
Q10. What is the need for separation?
Ans. The following are the reasons for the separation:
to remove the undesirable constituents from mixture.
To obtain desirable substances from mixture.
To obtain highly pure substance.
Q11. Define sieving
Ans. The particles are separated on the basis of their size 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.
Q12. a boy has got a mixture containing salt , tea leaves &
oil. How will he separate the components?
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Ans. First he will sieve the solution to obtain tea leaves. Then
the solution would be left with salt & oil ,
now he will use distillation to separate salt & oil.On
heating oil will go from one beaker to another &
then decantationis employed to separate oil from mixture.
Q13. Identify the following as pure substances &
mixtures:
Silver, salt, sharbat & jam.
Ans. Silver Pure substance
Salt Pure substance
Sharbat mixture
Jam mixture
Q14. A boy has prepared a saturatyed solution of sugar in water
by dissolving 50g sugar in water. What
will happen
he will add more of sugar in the solution at the same
temperature.
He will add more of sugar in that solution at high
temperature.
He will allow the solution to coll.
Give explaination for each of these.
Ans. a) Sugar will not dissolve any more .
B) at high temperature , sugar will start dissolving.
C) When he will allow the above obtained solution to cool, the
crystals of sugar will be formed & settle
down.
