Class-6 Science, Chapter-5 Separation of Substances, Solutions and additional exercises in line with NCERT book / CBSE Syllabus

Chapter 5
Separation of Substances
=========================================================

Additional Exercises

Exercises from Textbook

Tables from Textbook

Additional Exercises

Choose the correct answer:

1-    If we can not dissolve more salt in the given amount of water, now the solution is said to be

a.    Saturated (√)

b.    Evaporated

c.    Filtered

2-    Which of the following methods cannot be used to separate salt, sand and water from their mixture

a.    Decantation

b.    Evaporation

c.    Winnowing

3-    Churning of milk or curd  to separate butter is called

a.     Boiling

b.    Centrifugation (√)

c.     Filtration

4-    Device or apparatus used to extract cream from milk is called-

a.    Separating funnel

b.    Filter paper

c.    Magnet

d.    Centrifuge (√)

5-    Which technique is used to purify dirty water?

a.    Centrifugation

b.    Evaporation

c.    Sedimentation (√)

d.    Decantation

Match the column:

A	B
Separation of wheat and husk from their mixture	Threshing
Separation of grains from stalks	Centrifugation
Separation of butter from curd	Decantation followed by sedimentation
Separation of sand from water	Winnowing with bamboo winnower

Ans-

A	B
Separation of wheat and husk from their mixture	Winnowing with bamboo winnower
Separation of grains from stalks	Threshing
Separation of butter from curd	Centrifugation
Separation of sand from water	Decantation followed by sedimentation

Science Class-7

Answer the following in one word:

1-    The process of conversion of water vapour into its liquid form.
Condensation

2-    The process of conversion of water into its vapour.
Evaporation

3-    The method of separating tea leaves from prepared tea through a strainer.
Filtration

4-    Method to separate two liquids that do not mix with each other.
Decantation

5-    Method to separate pebbles And stones from sand at a construction site.
Sieving

6-    The machine used by farmers to separate grain from stalks et cetera.
Thresher

Fill in the blanks

1-    Threshing is the process in which stalks are beaten to free the grain seeds.

2-    Fruits and vegetable juices are filtered before drinking to separate seeds and solid particles of pulp.

3-    We use the process of evaporation to separate salt from a mixture of water and salt.

4-    Clouds are formed by condensation of water vapours.

5-    A solution is said to be saturated if it can not dissolve more of the substance in it.

6-    Large quantities of salt can be dissolved in water on heating.

Define following terms

(a)  Hand picking

(b)  Threshing

(c)  Winnowing

(d)  Sieving

(e)  Sedimentation

(f)   Decantation

(g)  Condensation

Hand picking- Hand picking is the process for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses.

The quantity of such impurities is not very large.

Threshing- The process in which stalks are beaten to free the grain seeds is called threshing.

Machine called thresher is used to thresh large quantities of grain.

Winnowing- Winnowing is the process of separating heavier and lighter components of a mixture by wing or by blowing air.

Sieving- Sieving is the process of separating components of a mixture which are different in size. Mixture is poured on a sieve and fine particles pass through the whole of sieve while the bigger particles remain on sieve.

Sedimentation- When the heavier component in a mixture settles after water is added to it, the process is called sedimentation.

Decantation- After the sedimentation of insoluble substance at the bottom, upper part is carefully poured in a separate container. This process is called decantation.

Condensation- The process of conversion of water vapour into its liquid form is called condensation.

Answer these questions:

Q. Write four examples of separation from day to day life.
Ans- Four examples of separation from day to day life are as follows:

1-    Tea leaves are separated from the liquid with a strainer while preparing tea.

2-    Grain is separated from stalks while harvesting.

3-    Milk or curd is churned to separate the butter.

4-    We gin cotton to separate its seeds from the fibre.

Q. Why is the sea water salty?
Ans- The seawater is salty because of the continuous evaporation of water from sea surface.

Exercises from Textbook

Q. Why do we need to separate different components of a mixture? Give two examples.
Ans- We need to separate different components of a mixture because of the following reasons: 

1.    To separate harmful or non-useful substances.

2.    To separate even useful components if we need to use them separately.

Examples -

1.    Milk or curd is churned to separate the butter.

2.    We gin cotton to separate its seeds from the fibre.

Q. What is winnowing? Where is it used?
Ans- Winnowing is the process of separating heavier and lighter components of a mixture by wind or by blowing air.
Winnowing is used when a mixture has heavier and lighter components. For example separating husk from wheat.

Q. How will you separate husk or dirt particles from a given sample of pulses before cooking?
Ans- For separating husk and dirt particles from a given sample of pulses before cooking, we will use the following methods:

1-    Winnowing - it will help to remove husk from pulses.

2-    Sieving- sieving will help to remove fine dirt from pulses.

3-    Hand picking - slightly larger sized impurities like the pieces of dirt, stone and husk can be removed by hand picking.

Q. What is sieving? Where is it used?
Ans- Sieving is the process of separating components of a mixture, which are different in size. Fine particles pass through the holes of a sieve while the bigger impurities remain on the sieve.
Sieving removes pieces of stone, stock and husk that may still remain with wheat after threshing and winnowing.

Q. How will you separate sand and water from their mixture?
Ans- We will allow the mixture of sand and water to remain still for sometime. The sand will settle at the bottom (sedimentation). Now we will slightly tilt the vessel and collect water in a separate container. (Decantation).

Q. 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.
We will pour the mixture in a sieve. Fine particles of flour will pass through the holes of sieve while the bigger particles of sugar will remain on the sieve.

Q. How would you obtain clear water from a sample of muddy water?
Ans- We will obtain clear water from a sample of muddy water in the following steps:

1-    Let the muddy water stand still for half an hour. (soil will settle at the bottom)

2-    Let the water from the top flow into another glass. (decantation)

3-    If the water in the second glass is still muddy, we can use a filter paper to remove soil and get clear water.

4-    Further impurity can be removed by swirling a piece of alum in the water. (loading)

Fill up the blanks

1-    The method of separating seeds of paddy from its stalks is called threshing.

2-    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.

3-    Salt is obtained from seawater by the process of evaporation.

4-    Impurities settled at the bottom when muddy water was kept overnight in the bucket. A water was then poured off from the top. The process of separation used in this example is called decantation followed by sedimentation.

True or false?

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

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

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

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

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?
More sugar can be dissolved before adding ice to the lemonade. Larger quantities of solutes can be dissolved in water at a higher temperature.

Tables from Textbook

Table 5.1 why do we separate substances?
In column 1 of table 5.1, are given a few processes of separation. The purpose of separation and the way separated components are used is mentioned in Column 2 and 3 respectively. However, the information given in Column 2 and 3 is jumbled up. Can you match each process and the way separated components are used?

Separation Process	Purpose for which we do the separation	What to do with the separated components?
Separate stones from rice	To separate to different but useful components.	We throw away the solid component.
Churning milk to obtain butter	To remove non-useful components.	We throw away the impurities.
Separate tea leaves	To remove impurities or harmful components.	We use both the components.

Ans-

Separation Process	Purpose for which we do the separation	What to do with the separated components?
Separate stones from rice	To remove impurities or harmful components.	We throw away the impurities.
Churning milk to obtain butter	To separate to different but useful components.	We use both the components.
Separate tea leaves	To remove non-useful components.	We throw away the solid component.

Table 5.2

Substance	Number of spoons of substance that dissolves in water
Salt	2
Sugar	3

Activity / Project

1 - Visit a nearby dairy and make a report about the processes used to separate cream from milk.

2- How is butter prepared from curd at your home.

3-  What is the source of water supply at your home and which technique do you apply to separate out the impurities from it?

4 - You have tried a number of methods to separate impurities like mud from water. Sometimes, the water obtained after employing all these processes could still be a little muddy. Let us see if we can remove even this impurity completely. Take this filtered water in a glass. Tie a thread to a small piece of alum. The pieces of alum in water and soil. The water become clear? What happened to the mud? This process is called loading.

Back to Table of Contents