NCERT Science Class-VI Chapter-5: Separation of Substances Solutions

 

Exercises

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

 Ans: Before using a substance, we need to separate harmful or non-useful substances that may be mixed with it. Sometimes, we separate even useful components if we need to use them separately.

For example:

• Milk or curd is churned to separate the butter
• Rice or pulses are usually washed before cooking. When we add water to these, the impurities like dust and soil particles get separated.

 

Q 2: What is winnowing? Where is it used?

Ans: Winnowing is the method of separating components of a mixture containing heavier and lighter components by wind or by blowing air. This method is commonly used by farmers to separate lighter husk particles from heavier seeds of grain.

 

Q 3: How will you separate husk or dirt particles from a given sample of pulses before Cooking?

 Ans: Husk or bigger pieces of dirt particles can be removed from a sample of pulses by handpicking.

 

Q 4: What is sieving? Where is it used?

Ans: Sieving is the process of filtering components of a mixture of different sizes. Sieving allows fine particles to pass through the holes of the sieve, while the bigger impurities remain on the sieve.

Sieving is used in flour mills to separate broken particles of grains from flour.  It is used at home, construction sites to separate pebbles and stones from sand.

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

 Ans: To separate sand and water from their mixture, we follow the following steps:

• Leave mixture to stand undisturbed for some time in a container.
• Sand settles at the bottom of the container. It is called sedimentation.
• Gently pour the water in another container (called decantation).
• We may also use filter paper to remove fine particles of sand (called filtration)

 

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

 Ans: Yes, it is possible to separate sugar mixed with wheat flour. This can be done through the process of sieving The mixture of sugar and wheat flour is allowed to pass through a sieve. The fine wheat flour passes through the sieve while sugar remains on the sieve.

 

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

Ans: Following steps are required to obtain clear water from muddy water:

• Allow muddy water to stand undisturbed in a container.
• After sometime, mud settles at the bottom of the container. This process is called sedimentation.
• Upper layer is clear water.
• Pour the clear water gently in another container. This process is called decantation.
• To remove finer impurities we can filter this water again with the help of filter paper. This process is called filtration.

 

Q 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 ___________.

Ans:

(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 sedimentation and decantation.

 

Q 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.

 Ans:

(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)

 

Q 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?

Ans: We should add ice after dissolving sugar because the dissolving power of water decreases with decrease in temperature. So, if we add ice before dissolving sugar, less amount of sugar will get dissolved.

 

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