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Page No 59:

Question A:

Solve the following crossword puzzle:
Figure

Across
1. Wheat bran is removed from flour using this method
3 It is the clear liquid obtained after filtration
4. It is the major component of a solution
5. The process of separating grains from chaff of husk

Down
1. A homogeneous mixture of solute and solvent
2. It is the minor component of a solution

Answer:

Page No 59:

Question B.1:

A mixture of wheat and husk can be separated by
(a) hand-picking
(b) sieving
(c) threshing
(d) winnowing

Answer:

(c) winnowing
Farmers use this method to separate grain (here wheat) from husk. The mixture of grain and husk are dropped from a height. The heavier grain particles falls straight down while the lighter husk particles are taken away by wind and collected separately at a short distance.

Page No 59:

Question B.2:

A mixture of water and sulphur can be separated by
(a) evaporation
(b) filtration
(c) decantation
(d) sieving

Answer:

(b) filtration
The insoluble sulphur particles are separated from water by filtration method.



Page No 60:

Question 1:

Why is frozen carbon dioxide called dry ice? Is it because it does not change into liquid on warming?

Answer:

Yes, because dry ice, placed at room temperature, gets converted to gas directly without getting converted to liquid. Hence, frozen or solid carbon dioxide is called dry ice. This process of conversion of solid to gas directly without getting converted to liquid is called sublimation. Thus, dry ice is stored under high pressure.

Page No 60:

Question 2:

Why do we call sea water a mixture?

Answer:

Seawater comprises 96.5% water, 2.5% salts and small quantities of dissolved inorganic and organic materials. It comprises a mixture of salts. It consists of various types of constituents mixed up in different proportions. Thus, it is considered a mixture and not a pure substance.

Page No 60:

Question 3:

Why do some people tie a thin piece of cloth on the mouth of water taps?

Answer:

Tap water is not comprised of only one substance. It is a mixture of water and other substances (contaminants). It may contain dissolved chemicals, undissolved substances, sand, small stones, dead insects, worms, etc. Thus, in order to filter the water from contaminants, some people tie a thin piece of cloth on the mouth of water taps. 

Page No 60:

Question B.3:

A best option to obtain salt from sea water is
(a) evaporation
(b) filtration
(c) decanation
(d) sedimentation

Answer:

(a) evaporation
Evaporation is the most appropriate method to collect solids dissolved in water. Seawater gets evaporated and leaves behind solid salt.

Page No 60:

Question B.4:

Which one of the following in an example of pure substance?
(a) air
(b) salt
(c) water
(d) gold

Answer:

(d) gold
Gold is an element and it is made up of only one kind of atoms. Hence, gold is a pure substance.

Page No 60:

Question B.5:

Fresh juice of fruit is sieved by fruit vendors by
(a) strainer
(b) sieve
(c) hands
(d) machine

Answer:

(a) strainer
 Strainer separates fruit seeds and other non-edible particles from fruit juice.

Page No 60:

Question C:

Fill in the blanks:
1. ......................... is used to separate chaff from food grains.
2. A ......................... substance has definite composition and properties.
3. Separation of liquid after sedimentation is called ......................... .
4. ......................... is obtained from sea water by the process of evaporation.
5. ......................... is the process of changing liquid into vapour.

Answer:

1. Winnowing is used to separate chaff from food grains.

2. A pure substance has definite composition and properties.

3. Separation of liquid after sedimentation is called decantation.

4. Common salt
is obtained from seawater by the process of evaporation.

5. Evaporation is the process of changing liquid into vapour.

Page No 60:

Question D:

Match the items is Column A with the items in Column B

Column A Column B
1. Separation of husk from grains (a) Hand-picking
2. Conversion of liquid into vapour (b) Filtration
3. Separating pebbles from pulses (c) Threshing
4. Separating chalk powder from water (d) Evaporation
5. Separating grains from the stalk (e) Winnowing
  (f) Sieving

Answer:

 

Column A Column B
1. Separation of husk from grains (e) Winnowing
2. Conversion of liquid into vapour (d) Evaporation
3. Separating pebbles from pulses (a) Hand-picking
4. Separating chalk powder from water (b) Filtration
5. Separating grains from the stalk (c) Threshing

Page No 60:

Question E:

Write True (T) or False (F) against the following statements in the given brackets:
1. Supernatant is the liquid found above the sediment. ( )
2. A pure substance has a fixed specific gravity. ( )
3. Threshing is following by winnowing. ( )
4. The process of winnowing is used to remove pebbles form grains. ( )
5. Sugar can be separated from sugar solution by decantation. ( )

Answer:

1. True

2. True

3. False
Winnowing is followed by threshing.

4. False
Hand-picking is the method used to remove pebbles from grains. Winnowing is the method used to separate husk from grains.

5. False
Sugar is separated from sugar solution by evaporation. The water content in the sugar solution gets evaporated, leaving behind sugar.



Page No 61:

Question A.1:

What type of mixtures can be separated by hand-picking?

Answer:

Mixtures in which the components differ in size, shape and colour are separated by hand-picking.

Page No 61:

Question A.2:

What is the importance of a thresher to a farmer?

Answer:

Threshers are machines used for threshing (separating grains from stalks by beating them). When the fields are big, threshing helps in cheaper, quicker and more efficient separation of grains, compared to treading with animals.

Page No 61:

Question A.3:

What properties would you look for to prove whether a particular substance is pure of impure?

Answer:

The properties that help us to prove whether a particular substance is pure or impure are boiling point, melting point and specific gravity.



Page No 62:

Question A.4:

Name the process by which pebbles and stones are removed from sand.

Answer:

Sieving is the process used to remove pebbles and stones from sand. The impurities in sand such as pebbles and stones differ in size and can be easily removed by sieving.

Page No 62:

Question A.5:

What is a mixture?

Answer:

Mixture is a substance that consists of two or more components or constituents mixed up in different proportions.

Page No 62:

Question B.1:

What is threshing and how is it done?

Answer:

Threshing is a method of separating grain from the stalk.
The reaped crop is beaten so that the grain is separated from the stalk and grain's outer cover called husk or chaff is loosened. Usually, threshing is done by beating the reaped crop by sticks and allowing animals like bullocks and buffaloes to tread the crop. In case of big fields, threshing is done with the help of machines called threshers.

Page No 62:

Question B.2:

What is sieving and where do we use it?

Answer:

Sieving is a method of separating the components of a mixture if they differ in size.
We use this method to separate wheat flour from its bran. Here, fine powdered particles of wheat flour pass through the â€‹sieve and the huge bran particles stay on the sieve. Sieving is also used to separate tea leaves from the liquid and seeds from fruit juice with the help of a strainer.

Page No 62:

Question B.3:

What principle do we use in the separation of mixtures?

Answer:

The principle used in the separation of a mixture employs a special property of one of the components of the mixture. For example, iron pieces mixed with sand can be separated using a magnet, as iron gets attracted towards the magnet.

Page No 62:

Question B.4:

How is winnowing done?

Answer:

Winnowing is a process of separating grains from husks.
In this process, the mixture of grain and husk is dropped from a height. The heavier grain particles fall down
straight to the ground while the lighter husk particles are taken away by wind and are collected separately at a small distance from the pile of grains.

Page No 62:

Question B.5:

How will you separate sugar and chalk powder?

Answer:

A mixture of sugar and chalk powder would be separated by mixing them in water.
Sugar is soluble in water, whereas chalk powder is not. Chalk powder can be obtained from the mixture by filtration wherein chalk powder stays on the filter paper as residue and sugar solution is filtered out. Sugar can be separated from water by evaporation. When the solution becomes concentrated, the sugar gets crystallized on cooling the solution.

Page No 62:

Question B.6:

Why do we need to separate different components of a mixture?

Answer:

We need to separate different components of a mixture as to:

  • Eliminate unnecessary constituents present in the mixture
  • Obtain pure substances from the mixture
  • Collect useful components from the mixture
 
 

Page No 62:

Question B.7:

How will you separate salt from brine solution?

Answer:

Separation of salt from brine solution is done by evaporation. In this method, brine solution is heated until all the water gets evaporated from it. The crystals of salt are left behind after cooling the solution.

Page No 62:

Question B.8:

Differentiate between saturated and unsaturated solutions.

Answer:

Saturated solution Unsaturated solution
A solution in which no more solute can be dissolved in the solvent is called saturated solution. A solution in which the solvent is capable of dissolving more solute than it already has is called unsaturated solution.

Page No 62:

Question B.9:

What do you understand by supersaturated solution? Give an example.

Answer:

A solution that contains more amount of solute than what could be dissolved by the solvent at normal temperature is called supersaturated solution, for example, carbonated water present in carbonated drinks.

Page No 62:

Question C.1:

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

Answer:

We can obtain clear water from a sample muddy water by sedimentation and decantation. It can be done by following steps:

  • First, set aside the mixture of mud and water container undisturbed for sometime.
  • After a while, we can examine that the mud particles start to settle at the base of the container, forming sediment. This process is called sedimentation.
  • The clear liquid above the sediment is called supernatant. This supernatant is transferred to another container without disturbing the sediment. This process of shifting clear liquid from the container without disturbing the sediment is called decantation.
In this way, clear water is separated from muddy water.

Page No 62:

Question C.2:

How will you separate a mixture of common salt, sand and iron fillings?

Answer:

Mixture of common salt, sand and iron filings can be separated as follows:

  • Iron filings are magnetic in nature and are removed with the help of a magnet. Iron filings get attracted to the magnet and are collected separately from common salt and sand.
  • Now, add water to salt and sand mixture. Salt gets dissolved in water, whereas sand remains undissolved. Sand can be obtained from the mixture by filtration wherein sand is left on the filter paper as residue and salt solution is filtered out.
  • Salt can be separated from water by evaporation. When the solution becomes concentrated, salt gets crystallized on cooling the solution.

Page No 62:

Question C.3:

What are pure substances?

Answer:

Pure substances consist of only one type of particles and have similar composition. All elements and compounds are examples of pure substances.
Properties like
boiling point, melting point and specific gravity help us to determine the purity of a particular substance.

Page No 62:

Question C.4:

Describe an activity to separate a mixture of sand and water.

Answer:

Take an empty beaker and fill water to about half the level of beaker. Now, add some sand in the beaker containing water. Stir the mixture of sand and water well. Set it aside for some time.

After some time, sand particles will start settling at the base of the beaker, forming sediment. This process is called as sedimentation.

Now, transfer the supernatant (water) through a glass rod to another beaker without disturbing the sediment. This process is called decantation.

You will observe that clear water and sand get separated from the mixture of sand and water.

Page No 62:

Question C.5:

How will you separate a mixture of water and sulphur?

Answer:

A mixture of water and sulphur is separated by filtration. Sulphur is insoluble in water; therefore, it is separated easily with the help of filtration. Sulphur is obtained as residue on the filter paper and water is collected as filtrate in a beaker.

Page No 62:

Question C.6:

What is filtration? How is it useful to us?

Answer:

Filtration is a process of separating suspended particles from a liquid. It is carried out with the help of a filter paper.
Filtration process is very useful to us in the following ways:

  • It is used in making cottage cheese. Here, solid paneer is separated from its liquid by filtering it through muslin cloth.
  • Water that we receive is also filtered by passing through gravel, sand and charcoal.

Page No 62:

Question C.7:

What do you understand by solution? Explain it in terms of solute and solvent.

Answer:

A uniform (homogeneous) mixture of one or more materials (solute) dissolved in another material (solvent) is called solution. The component that gets dissolved in the solution is called solute and the component that dissolves the solute is called solvent.
For example, sugar dissolves in water and forms sugar solution. Here, sugar is the solute and water is the solvent.

Page No 62:

Question C.8:

Give two differences between pure substance and mixture.

Answer:

Pure substances Mixtures
Pure substances consist of only one type of constituents. Mixtures consist of two or more types of constituents.
Pure substances have specific and definite characteristics with uniform composition. Mixtures do not have specific and definite characteristics and the constituents are mixed up in different proportions.



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