Separation of Substances
Q19. How will you separate husk or dirt particles from a given
sample of pulses before cooking?
Ans. Husk or dirt particles from a given sample of
pulses can be removed by washing the pulses with water. Being heavier, pulses
will settle down in the bottom of the container whereas lighter particles will
keep floating in the water. This is called sedimentation. Dirty water can be
removed by the process of decantation by leaving behind pulses in the bottom of
Q20. What is sieving? Where is it used?
Ans. Sieving is a simple and convenient technique of
separating particles of different sizes by allowing the smaller particles to
pass through the holes of a sieve leaving the bigger particle in the sieve.
Uses of sieving
i. Used in
homes to separate flour from impurities such as husk, stalks and small pieces
ii. Used in
flour mill to separate broken particles of grain from flour.
iii. Used at the construction sites to
separate small pieces of stones from sand.
Q21. How will you separate sand and water from their mixture?
Sand is insoluble in water. So we can use two methods to separate sand and
water from the mixture.
Sedimentation & Decantation – Allow the
mixture to stand undisturbed for some time. Being heavier sand settles down at
the bottom of the container. This process is called sedimentation. Now slowly
pour the water into another container. This process is called decantation.
Filtration – Pour water on strainer or a
piece of cloth or a filter paper so that water passes through the strainer and
sand remains on the strainer.
Q22. Is it possible to separate sugar mixed with wheat flour? If
yes, how will you do it?
Yes, it is possible to separate sugar mixed with wheat flour by the process of
sieving. Allow the mixture to pass through the sieve. Fine particles of wheat
flour passes through the holes of the sieve whereas the bigger particles of
sugar would remain on the sieve.
Q23. 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?
We should add sugar before adding ice as sugar dissolves faster in warm water
than in cold water. We can dissolve more sugar in case of warm water.
Q24. How would you obtain clear water from a sample of muddy
We can obtain clear water from a sample of muddy water in the following ways:
Sedimentation and Decantation: Allow
mixture to stand still for sometimes so, that mud settles down at the bottom.
This process is called sedimentation. Now gently pour the water in another
container. This process is called decantation.
Filtration: Allow the mixture to pass
through the filter paper. Water will pass through the filter paper and mud will
get collected on the filter paper. This process is called filtration.
Q25. How will you separate the components of the following?
Green Chillies from pulao
Green gram from Chick pea
Pebbles from rice
Hand picking or sieving
Tea leaves from tea
Sieving or straining
Wheat bran from wheat flour
Sand and husk
Wheat, sugar and stalks
Stalks being lighter can be separated
by winnowing. Wheat and sugar can be separated by sieving.
Water and kerosene
Rice and sugar