Separation of Substances

NCERT Solution

Fill in the blanks
  1. The method of separating seeds of paddy from its stalks is called---------.

    Answer: Threshing
  2. 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 -------

    Answer: Filtration
  3. Salt is obtained from sea water by the process of -------

    Answer: Evaporation
  4. 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 separations used in this example is called------------

    Answer: Sedimentation and decantation

True or false?

  1. A mixture of milk and water can be separated by filtration.
  2. A mixture of powdered salt and sugar can be separated by the process of winnowing.
  3. Separation of sugar from tea can be done with filtration.
  4. Grain and husk can be separated with the process of decantation.

Answer; 1 False, 2 False, 3 False, 4 False

Answer the following questions

Why do we need to separate different components of a mixture? Give two examples.

Answer: A mixture may contain one or more unwanted substances which may be harmful. These impurities are harmful for our health so, we need to separate different components of a mixture. Examples: Pebbles are separated from rice and pulse. Petrol, diesel, kerosene, etc. are obtained from crude oil by a method called distillation.

What is winnowing? Where is it used?

Answer: The process of separation of grains from husk and hay with the help of wind is called winnowing. Farmers use this method for separating the grains from husk and hay.

Answer the following questions

How will you separate husk or dirt particles from a given sample of pulses before cooking?

Answer: For this, winnowing can be used.

What is sieving? Where is it used?

Answer: The process of separating solid constituents of different particle sizes; through a sieve is called sieving. Sieving is used while separating bran from flour. It is also used while separating pebbles from sand.

How will you separate sand and water from their mixture?

Answer: The mixture of sand and water can be separated by sedimentation and decantation.

Is it possible to separate sugar mixed with wheat flour? If yes, how will do it?

Answer: Yes, it is possible to separate sugar mixed with wheat flour. It can be done by the process of sieving.

How would you obtain clear water from a sample of muddy water?

Answer: We can get clear water from a sample of muddy water by the process of sedimentation, decantation and filtration. Coarser particles of soil would settle down at the bottom and partially clean water can be separated by decantation. The water thus obtained can be further clarified by filtration.

Lemonade is prepared by mixing lemon juice and sugar in water. You wish to add ice to cool it. Should you add to the lemonade before or after dissolving sugar? In which case would it be possible to dissolve more sugar?

Answer: Ice should be added after dissolving the sugar. Saturation level increases with increase in temperature and vice-versa is also true. So, it is possible to dissolve more sugar in water at room temperature rather than at lesser temperature.

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