NCERT Exemplar Problems Class 6 Science – Separation of Substances

Question 1:
Paheli bought some vegetables such as french beans, lady’s finger, green chillies, 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:
(d) Hand-picking method would be most appropriate for her to separate vegetables because vegetables can be picked up easily by hand one by one, and can be separated.

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:
(c) Churning is the method by which cream (fat content) from the milk is separated. So, he should prepare ’Lassi’ by the process churning.

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:
(b) Filtration method is used for separating insoluble substance from a liquid. But mixture of two liquids such as oil in water cannot be separated by this method. Also salt in water and sugar in milk are completely dissolved so, cannot be separated by filtration. So, cornflakes in milk can be separated by filtration.

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:
(d) The grains are separated from stalks (on which they grow) by the process of threshing. In this process stalks (of wheat, paddy, etc) are beaten to separate grains from the bundle of stalks.
Note: This method is based on the fact that the stalks (or stems) of the crop plant are soft material whereas the grains themselves are very hard.
Being soft, stalks can be broken into pieces on beating but the grains remains unaffected.

Question 5:
Four mixtures are given below:

1. Kidney beans and chickpeas
2. Pulses and rice
3. Riceflakes 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:
(d) Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air. Rice flakes and potato wafers are lighter substances in the mixture, so these are separated from the given mixture by 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:
(b) The most suitable method to separate the grains from the flour is by sieving.
Sieving is used to separate those solid mixture which have components of different sizes.

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:
(b) By decantation and then by filtration ghee can be separated from the residue.
Note Decantation is the process of pouring out the liquid without disturbing the sediment.

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:
(b) By the process of evaporation we can get back solid copper sulphate from the solution. The process of evaporation for separating a mixture is based on the fact that liquids vaporise easily whereas solids do not vaporise easily.

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:
(c) The droplets of water on the inner surface of bottle were formed due to evaporation and condensation.
Note The process oj conversion oj water vapour into liquid form is called condensation.

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 vapour
(d) Condensation of atmospheric water vapour
Solution:
(d) Water droplets on the outer surface of glass is formed due to condensation of atmospheric water vapour. Actually the water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

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:
Ravi would win the game because Ravi took hot boiling milk and hot milk at higher temperature would dissolve more amount of sugar and also solubility increases with temperature. So, Ravi would be able to dissolve maximum amount of sugar in milk.

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:

1. hand-picking
2. Grains (seeds)
3. sieving
4. sedimentation
5. solute (solid), 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:
(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:
Winnowing is used to separate lighter husk particles from heavier seeds of grains by wind or by blowing air.
This method is based on the fact that husk is very light whereas wheat grains are comparatively heavy. The mixture is allowed to fall from a height by shaking winnowing basket continuously. The husk particles are carried away by the wind to a greater distance. The wheat grains, being heavy, fall down vertically to the ground and form a heap of wheat grains.

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

Solution:
(c) The correct matching is as given:
(a)—(iii), (b)—(iv), (c)—(v), (d)—(ii), (e)—(i)

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:
(a) They will mix salt with water within a certain amount to make salt solution. Hence, Sarika will make a better salt solution.
(b) Saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amount of that substance will appear as a precipitate. Mohan’s solution would be saturated because in Mohan’s case, some salt would remain undissolved and settled at the bottom of the glass.

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

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:

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

They got a good price as they used appropriate methods of separation to get good quality of flour (atta).

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:
Steps for the separation of salt, sand, oil and water
First we will use decantation method to separate oil and water. Water being heavier, forms the lower layer and oil being lighter, forms the upper layer in the beaker. We can decant off the upper layer of oil into another beaker carefully.
Then by the process of filtration sand can be separated from water. The filtrate obtained contains the mixture of salt and water. The salt dissolved in water can be separated by the process of evaporation.
The water present in salt solution will form water vapour and then the salt is left behind.
(a) Decantation

(b) Filtration

(c) Evaporation

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:
Steps for the separation of iron nails, salt, oil and water
Iron nails are separated from the mixture by using magnets. Then by using decantation oil and water is separated. Oil being lighter forms the upper layer in the beaker and we can decant off the upper layer of oil.
Now, the mixture contains dissolved salt and water. Salt can be obtained from the water by the process of evaporation. The water present in salt solution will form water vapour and then the salt is left behind.