NCERT Solutions for Class 6 Science Chapter 5 Separation Of Substances

Q1 ) Why do we need to separate different components of a mixture? Give two examples.

Answer :

(1) When two or more substances are mixed together we call it a mixture.

(2) Separating the mixture is necessary because some components may not be useful or may spoil the useful component of the mixture.

(3) Therefore, it is necessary to separate the mixture to obtain the pure substance.


Example:

(a) Stone pieces from wheat, rice, or pulses are picked out by hand.

(b) Sand mixed in water is separated by sedimentation.

(c) Tea leaves are separated from the liquid with a strainer while preparing tea.

Q2 ) What is winnowing? Where is it used?

Answer :

(1) The method of separating the components from a mixture is known as winnowing.

(2) In this method, heavier and lighter components of a mixture are separated by wind or by blowing air.

(3) This method is used by farmers to separate lighter husk particles from heavier seeds of grain.

Q3 ) How will you separate husk or dirt particles from a given sample of pulses before cooking?

Answer :

(1) Husk or dirt particles can be separated by the winnowing method.

(2) Undesirable substances such as pieces of stone in the pulse or rice can be separated by hand-picking but the husk is mixed with the pulse then we separate it by winnowing.

(3) It is used to separate the heavier and lighter components of a mixture by wind or by blowing air.

(4) In this method, the mixture of husk and seeds of grains are taken on a plate and are made to fall down from a height up to our shoulders.

(5) As the mixture falls down, the lighter husk is taken away by blowing air and the heavier grain seeds fall down to make a heap.

Q4 ) What is sieving? Where is it used?

Answer :

(1) Sieving is a method in which fine particles are sieved through holes of the sieve while the bigger impurities remain on the sieve.

(2) Sieving is used in a flour mill to separate impurities like husk and stones from wheat before grinding it.

(3) It is also used at construction sites to separate pebbles and stones from sand.

(4) The size of the pore in the sieve depends on the size of the particles of the constituents to be separated.

Q5 ) How will you separate sand and water from their mixture?

Answer :

Sand and water can be separated by any of the following two methods:


(a) Sedimentation and decantation:

Mixture is kept undisturbed for some time. After some time, sand being heavier and insoluble in the water settles down at the bottom of the container. Now, water is poured into another container to separate it from the sand.


(b) Filtration:

Mixture of sand and water is passed through a filter paper (a filter with very fine pores). Sand particles being larger in size are retained by the filter paper and get separated from the water.

Q6 ) Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?

Answer :

Yes, it is possible to separate sugar mixed with wheat flour by following methods :


(1) Sieving method :

Sugar particles being larger in size are retained by the sieve whereas wheat flour will pass through it.


(2) Filtration method :

Mix sugar and wheat flour in water.Stir the solution to allow sugar to dissolve.Now filter the mixture. Filtrate contains sugar solution and residue will be wheat flour.

Q7 ) How would you obtain clear water from a sample of muddy water?

Answer :

We obtain clear water from a sample of muddy water by sedimentation, filtration, or decantation method.

1. Leave the muddy water for some time. And after some time, take a circular piece of filter paper and fold it. And make a cone.

2. Place the filter paper cone in a funnel.

3. Keep a beaker below that funnel.

4. Pour the muddy water slowly into a cone, using a glass rod clear water flows down the funnel and collects in the beaker below.

5. Take out the filter paper cone and open it out. Mud particles are seen on the paper.

Q8 ) Fill up the blanks.

(a) The method of separating seeds of paddy from its stalks is called ___________.
(b) 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 ___________.
(c) Salt is obtained from seawater by the process of ___________.
(d) 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 separation used in this example is called ___________.

Answer :

(a) The method of separating seeds of paddy from its stalks is called \( threshing \) .

(b) 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 \( filtration\) .

(c) Salt is obtained from seawater by the process of \( evaporation\) .

(d) 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 separation used in this example is called \( decantation \) .

Q9 ) True or false?

(a) A mixture of milk and water can be separated by filtration.
(b) A mixture of powdered salt and sugar can be separated by the process of winnowing.
(c) Separation of sugar from tea can be done with filtration.
(d) Grain and husk can be separated with the process of decantation.

Answer :

(a) A mixture of milk and water can be separated by filtration.\(\rightarrow \) FALSE

REASON: No, filtration is used for the separation of solid components of the mixture from the liquid. But here both the components are liquids.


(b) A mixture of powdered salt and sugar can be separated by the process of winnowing. \(\rightarrow \) FALSE

REASON: No, winnowing is used to separate heavier particles from the lighter particles which can be blown away by the wind. But here both sand and sugar are heavy particles.


(c) Separation of sugar from tea can be done with filtration. \(\rightarrow \) FALSE

Reason: No, separation of sugar from tea can not be done with filtration because sugar is soluble in water.


(d) Grain and husk can be separated with the process of decantation. \(\rightarrow \) FALSE

REASON: No, decantation is used to separate insoluble solid components from the liquid component.

Q10 ) 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?

Answer :

(1) We should add ice to the lemonade after dissolving sugar.

(2) It is possible to dissolve more sugar before adding ice because as the temperature is decreased, the dissolving power of water also gets decreased.