NCERT Exemplar Solutions Class 6 Science Separation of Substances

Question 1:  Paheli bought some vegetables such as French beans, lady’s finger, green chilies, brinjals and potatoes all mixed in a bag. Which of the following methods of separation would be most appropriate for her to separate them?

a)      Winnowing

b)      Sieving 

c)       Threshing

d)       Hand-picking

Solution 1:  The right thing for which selection is made is d) Hand-picking.

She can be easily picked up vegetable one by one through hands and separate them. So hand picking method would be most appropriate for her to separate mixed vegetables.

Question 2: Boojho’s grandmother is suffering from diabetes. Her doctor advised her to take ‘lassi’ with less fat content. Which of the following methods would be most appropriate for Boojho to prepare it?

a)      Filtration

b)      Decantation

c)       Churning

d)      Winnowing

Solution 2:  The right thing for which selection is made is c) Churning.

Churning method would be most appropriate for Boojho to prepare ‘lassi’ with less fat content for his grandmother. Churning is the process of shaking up cream or whole milk to make butter and using this method Boojho can easily separate fat content (butter or cream) from ‘lassi’.

Question 3:  Which of the following mixtures would you be able to separate using the method of filtration?

a)      Oil in water

b)      Cornflakes in milk

c)       Salt in water

d)      Sugar in milk

Solution 3:  The right thing for which selection is made is b) Cornflakes in milk.

Filtration is a physical, biological or chemical operation that separates solid matter and fluid from a mixture with a filter medium that has a complex structure through which only the fluid can pass. In the above given mixtures, salt in water and sugar in milk are completely dissolve solution. And oil in water mixture, they both are liquid. So we cannot separate them by filtration method. But by using filtration method on Cornflakes in milk mixture, we can separate both of them because cornflakes are insoluble in milk.

Question 4:  Which amongst the following methods would be most appropriate to separate grains from bundles of stalks?

a)      Hand-picking

b)      Winnowing

c)       Sieving

d)      Threshing

Solution 4: The right thing for which selection is made is d) Threshing.

Threshing methods would be most appropriate to separate grains from bundles of stalks.

Threshing is the process of loosening the edible part of grain (or other crop) from the straw to which it is attached. Threshing may be done by beating the grain using a flail on a threshing floor.

Question 5:  Four mixtures are given below:

1. Kidney beans and chickpeas
2. Pulses and rice
3. Rice flakes and corn
4. Potato wafers and biscuits

Which of these can be separated by the method of winnowing?

a)      (1) and (2)

b)      (2) and (3)

c)       (1) and (3)

d)      (3) and (4)

Solution 5:  The right thing for which selection is made is d) (3) and (4).

Winnowing is an agricultural method developed by ancient cultures for separating heavier and lighter components of a mixture. In its simplest form, it involves throwing the mixture into the air so that the wind blows away the lighter components, while the heavier components fall back down. In above given mixtures, Rice flakes and potato wafers are lighter substances in the mixture, so these can be easily separated from the mixture by the method of winnowing.

Question 6:  While preparing chapattis, Paheli found that the flour to be used was mixed with wheat grains. Which out of the following is the most suitable method to separate the grains from the flour?

a)      Threshing

b)      Sieving

c)       Winnowing

d)      Filtration

Solution 6:  The right thing for which selection is made is b) Sieving.

Sieving is the most suitable method to separate the grains from the flour.

Sieving is the process of separating solid mixture particles by size.

Question 7:  You might have observed the preparation of ghee from butter and cream at home. Which method(s) can be used to separate ghee from the residue?

1. Evaporation
2. Decantation
3. Filtration
4. Churning

Which of the following combinations is the correct answer?

a)      (1)and (2)

b)      (2) and (3)

c)       (2) and (4) 

d)      Only (4) 

Solution 7:  The right thing for which selection is made is b) (2) and (3).

Decantation and then Filtration method(s) can be used to separate ghee from the residue.

Decantation is a process for the separation of mixtures of immiscible liquids (not forming a homogeneous mixture when mixed.) or of a liquid and a solid mixture. To put it in a simple way decantation is separating an immiscible solution by transferring the top layer of the solution to another container.

Question 8:  In an activity, a teacher dissolved a small amount of solid copper sulphate in a tumbler half-filled with water. Which method would you use to get back solid copper sulphate from the solution?

a)      Decantation  

b)      Evaporation

c)      Sedimentation

d)      Condensation

Solution 8:  The right thing for which selection is made is b) Evaporation.

Evaporation method would use to get back solid copper sulphate from the solution.

Evaporation is the process by which water changes from a liquid to a gas or vapor. Evaporation is a unit operation that separates a liquid from solids by means of heat transfer via vaporization or boiling.

Question 9:  During summer, Boojho carries water in a transparent plastic bottle to his school. One day, he left his bottle in the school. The bottle still had some water left in it. The next day, he observed some water droplets on the inner surface of the empty portion of the bottle. These droplets of water were formed due to:

a)      boiling and condensation

b)       evaporation and saturation

c)       evaporation and condensation

d)      condensation and saturation

Solution 9:  The right thing for which selection is made is c) evaporation and condensation.

He observed some water droplets on the inner surface of the empty portion of the bottle. These droplets of water were formed due to evaporation and condensation process.
Condensation is the change of the physical state of matter from the gas phase into the liquid phase, and is the reverse of vaporization.

Question 10:  Paheli asked for a glass of water from Boojho. He gave her a glass of ice cold water. Paheli observed some water droplets on the outer surface of the glass and asked Boojho, how these droplets of water were formed? Which of the following should be Boojho’s answer?

a)      Evaporation of water from the glass

b)      Water that seeped out from the glass

c)       Evaporation of atmospheric water vapor

d)      Condensation of atmospheric water vapor

Solution 10:  The right thing for which selection is made is d) Condensation of atmospheric water vapor.

Water droplets on the outer surface of glass are formed because of condensation of atmospheric water vapor.

Condensation can produce water droplets on the outside of glasses of cold water. When warm air hits the cold surface of glass, it reaches its dew point and condenses. This leaves droplets of water on the glass.

Very Short Answer Type Questions

Question 11:  Sheela, Saima and Ravi have to dissolve maximum amount of sugar in the same amount of milk, so as to win in a game. Ravi took hot boiling milk, while Saima took ice cold milk. Sheela managed to get milk at room temperature. Whom do you think would win the game and why? 

Solution 11:   Ravi would win the game because he   took hot boiling milk for dissolve sugar. Hot milk can dissolve sugar easily and quickly while in case of cold milk it takes time to dissolve because hot milk is at higher temperature and also solubility increases with temperature. 

Question 12:  Fill in the blanks. 

1. Small pieces of stones can be removed from rice by …………
2.  ………….. are obtained from stalks by threshing.
3. Husk from wheat flour is generally removed by …………..
4. The process of settling of heavier particles is called ………….
5. Filtration is helpful in separating an insoluble ………….. from a ………………  

Solution 12: 

1. Small pieces of stones can be removed from rice by Hand-picking.
2. Grains (seeds) are obtained from stalks by threshing.
3. Husk from wheat flour is generally removed by Sieving.
4. The process of settling of heavier particles is called Sedimentation.
5. Filtration is helpful in separating an insoluble Solute (solid) from a solution (liquid). 

Question 13:  State whether the following statements are true or false. 

a)      A mixture of oil and water can be separated by filtration. 

b)      Water can be separated from salt by evaporation. 

c)       A mixture of wheat grains and wheat flour can be separated by sieving. 

d)      A mixture of iron filings and rice flour can be separated by magnet. 

e)      A mixture of wheat grains and rice flakes can be separated by winnowing. 

f)       A mixture of tea leaves and milk can be separated by decantation.

Solution 13: 

a)      False (A mixture of oil and water can be separated by decantation.) 

b)      True 

c)       True 

d)      True 

e)      True 

f)       True 

Short Answer Type Questions

Question 14:  Name and describe briefly a method which can be helpful in separating a mixture of husk from grains. What is the principle of this method?

Solution 14:   Winnowing method can be helpful in separating a mixture of husk from grains by blowing air. Winnowing is an agricultural method developed by ancient cultures for separating heavier seeds of grain from lighter chaff or husk. The principle of this method involves throwing the mixture into the air so that the wind blows away the husk, while the grains fall back down for recovery. In this method, a shaped basket (Winnowing fan) shaken to raise the husk. 

Question 15:  Match the mixtures in Column I with their methods of separation in Column II.

Solution 15: The correct matching of the mixtures with their methods of separation is as follows:

Long Answer Type Questions

Question 16:  Both Sarika and Mohan were asked to make salt solution. Sarika was given a teaspoonful of salt and half a glass of water whereas; Mohan was given twenty teaspoonful of salt and half a glass of water.
(a) How would they make salt solutions?
(b) Who would be able to prepare saturated solution?

Solution 16: (a) they will make salt solutions by adding or mixing certain amount of salt in water and Sarika would be able to make better salt solution with a teaspoonful of salt and half a glass of water. (b)  A solution which cannot dissolve further amount of solute at a particular temperature is called saturated solution. So, Mohan would be able to prepare saturated solution. When Mohan keep adding twenty teaspoonsful of salt in half a glass of water, a time will reach when no more salt will dissolve in the water and salt will settle down at the bottom.

Question 17:  Paheli was feeling thirsty but there was only a pot of water at home which was muddy and unfit for drinking. How do you think Paheli would have made this water fit for drinking if the following materials were available to her? Alum, tub, muslin cloth, gas stove, thread, pan and lid.

Solution 17:  Paheli can make this water fit for drinking by working on following sequence:

Step 1: firstly, filter water by muslin cloth.

Step 2: take alum that tied with a thread and swirl in water then leave that water untouched for some time.

Step 3: Now, take another container or tub and the clear liquid above the impurities is pour into it through decantation process.

Step 4: boil this water on gas stove in covered pan with lid for at least 10 minutes.

Step 5: After boiling, let it cool. Now this water is fit for drinking. 

Question 18:  Read the story titled ‘Wise Farmer’ and tick the correct option to complete the story.
A farmer was sad/happy to see his healthy wheat crops ready for harvest. He harvested the crops and left it under the sun/rain to dry the stalks. To separate the seeds from the bundles of the stalk, he handpicked/threshed them.
After gathering the seed grains, he wanted to separate the stones and husk from it. His wife winnowed/ threshed them to separate the husk and later sieved/ hand-picked to remove stones from it. She ground the wheat grains and sieved/filtered the flour. The wise farmer and his wife got a good price for the flour. Can you tell why?

Solution 18:   The correct options to complete the story are as follows:

1. happy
2. sun
3. threshed
4. winnowed
5. hand-picked
6. sieved

The wise farmer and his wife got a good price for the flour because they used appropriate methods/process of separation to get good quality of flour.

Question 19:  You are provided with a mixture of salt, sand, oil and water. Write the steps involved for the separation of salt, sand and oil from the mixture by giving an activity along with the diagram.

Solution 19:   Steps for the separation of salt, sand, oil and water from the mixture with the diagram:

1. Decantation: - First, we will use decantation method to separate oil and water. Decantation method is separating an immiscible solution by transferring the top layer of the solution to another container.

In this case, Water being heavier, forms the lower layer and oil being lighter, forms the upper layer in the beaker. We will transfer the top layer of the oil to another container carefully.

2. Filtration: - Now, we can be separated sand from water by using filtration process. Filtration is a physical, biological or chemical operation that separates solid matter and fluid from a mixture with a filter medium that has a complex structure through which only the fluid can pass. The filtrate obtained contains the mixture of salt and water.

3. Evaporation: - now, evaporation process can be used to separate the salt dissolved in water. Evaporation is a unit operation that separates a liquid from solids by means of heat transfer via vaporization or boiling. The water present in salt solution will form water vapor and then the salt is left behind.

Question 20:  A mixture or iron nails, salt, oil and water is provided to you. Give step wise method to separate each component from this mixture?

Solution 20:   Step wise method to separate each component from the mixture of iron nails, salt, oil and water: -

1. Magnet: By using magnets, we will separate iron nails from the mixture.

2. Decantation method: Then by using decantation process, oil and water is separated from the mixture.  Oil being lighter, forms the upper layer in the beaker and we can carefully transfer it to another container.

3. Evaporation method: Now, the mixture only contains dissolved salt and water. Salt can be separated from the water by using the process of evaporation. We will boil the mixture of salt in water and after sometime form water vapor and then the salt is left behind.