Chapter 5 Separation of Substances

NCERT Solutions for Chapter 5 Separation of Substances for Class 6

Question 1 Why do we need to separate different components of a mixture? Give two
examples.

Answer: The mixture are separated into their components for various purposes such as:

1) To remove an undesirable component.

2) To remove harmful components.

3) To obtain the pure sample of a substance

4) To obtain a useful component.

For Example:

1) Stones are picked out by hand from wheat, rice.

2) Milk or curd is churned to separate the butter.

Question 2 What is winnowing? Where is it used?

Answer:

Winnowing is the method of separating husk from grains with the help of wind. Husk is very light whereas wheat grains are heavy.

The method of winnowing is used to separate husk from various types of grains like wheat, rice.

Question 3 How will you separate husk or dirt particles from a given sample of pulses before cooking.

Answer : Pulses bought from the market usually have dust or husk particles as impurities in them. So, pulses are always washed before cooking. When we add water to pulses taken in a vessel , then the impurities such as dust and husk particles get separated and go into water. Due to this the water becomes a little dirty. The pulses, being heavy, remain at the bottom of the vessel and dirty water is separated by decantation by tilting the vessel to one side.

Question 4 What is sieving? Where is it used?

Answer : A sieve is a shallow vessel having small holes at its bottom. The method of separating a mixture by using sieve is called Sieving.

Sieving is used to separate those solid mixtures which have components of different sizes. The mixtures having components of different sizes is put in sieve and the sieve is moved back and forth continuously. The smaller particles of the mixture cannot pass through the small holes of the sieve and remain behind in the sieve. The mixture gets separated into two components : one having small particles and the other having larger particles. The size of the holes of a sieve to be used depends on the size of the particles of the material to be separated from the mixture. Sieves of different sizes of holes are used for separating different substances.

For Example: The wheat flour which we bring from a flour mill is sieved by using sieve having very small holes.

Question 5 How will you separate sand and water from their mixture?

Answer : The sand and water mixture is taken in a beaker. It contains sand particles scattered throughout water. Allow the mixture of sand and water to stand undisturbed for some time. On keeping ,the heavier sand particles will settle down at the bottom of the beaker. This layer of sand is called sediment. The deposition of sand at the bottom of a beaker is called sedimentation. When the sand settles down , clear water is left above the layer of sand. We pour the clear water into another beaker gently with the help of a glass rod, without disturbing the sediment of sand. This process is called decantation. When all the clear water has been poured out, only sand is left at the bottom of the beaker. In this way a mixture of sand and water has been separated into sand and clear water by decantation.

Question 6 Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?

Answer : Yes, we can separate sugar mixed with wheat flour by the method of sieving.

The mixture of sugar and wheat flour is allowed to pass through a sieve. The sieve is then moved back and forth continuously. The wheat flour particles being smaller in size passes through the sieve whereas the sugar particles being larger in size remains on the sieve.

Question 7 How would you obtain clear water from a sample of muddy water?

Answer:  By the method of filtration, we can obtain clear water from muddy water. The muddy water is allowed to pass through filter paper. Solid mud particles will remain on the filter paper and the filtrate consist of clear water.

Question 8 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 churning.

(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 and sedimentation.

Question 9 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.
10. 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 :

(a) A mixture of milk and water can be separated by filtration. (False)

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

(c) Separation of sugar from tea can be done with filtration. (False)

(d) Grain and husk can be separated with the process of decantation. (False)

Question 10 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 : We should add sugar before adding ice. Sugar dissolves in warm water more quickly than in cold water. We can dissolve more sugar before mixing ice in water.