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Question 1:

Write one word for the following.

1. The process of beating harvested crops to separate grains from stalk. ...................
2. Separation of insoluble solids suspended in a liquid by allowing them to settle down ...................
3. The precess of pouring out the clear upper liquid without disturbing the sediments ...................
4. Changing of a liquid into gaseous form ...................
5. The substance that gets dissolved. ...................
6. The substance in which the solute dissolves ...................
7. The ability of a substance to dissolve in a given liquid ...................

Answer:

1. The process of beating harvested crops to separate grains from stalk Threshing
2. Separation of insoluble solids suspended in a liquid by allowing them to settle down Sedimentation
3. The process of pouring out the clear upper liquid without disturbing the sediments Decantation
4. Changing of a liquid into gaseous form Evaporation
5. The substance that gets dissolved Solute
6. The substance in which the solute dissolves Solvent
7. The ability of a substance to dissolve in a given liquid Solubility

Page No 46:

Question 1:

Grains or seeds are separated form the stalk by
(a) hand-picking
(b) winnowing
(c) sieving
(d) threshing

Answer:

(d) threshing
 

Grains or seeds are separated from the stalk by beating harvested crops, and this process is called threshing.

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Question 2:

Winnowing is used to separate the grain from the
(a) solvent
(b) sediment
(c) stalk
(d) chaff

Answer:

(d) chaff

Threshed grains may contain seed coverings and tiny pieces of stem or leaves collectively called chaff, which can be separated by winnowing.

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Question 3:

Hand picking is preferred when
(a) the quantity of the mixture is small
(b) the unwanted substance is present in large quantities
(c) the unwanted substance can dissolve
(d) the size or colour of the unwanted substance is the same as the useful one

Answer:

(a) the quantity of the mixture is small

Hand-picking is preferred when the quantity of the mixture is small, the unwanted substance is present in smaller quantities, and the size, shape and colour of the unwanted substance are different from those of the useful one.

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Question 4:

Condensation takes place only when
(a) water vapour hits a cold surface
(b) water vapour hits a hot surface
(c) a hot surface hits a warm surface
(d) water is heated

Answer:

(a) water vapour hits a cold surface

Condensation is the process by which water vapour condenses to form a liquid, and this happens when water vapour hits a cold surface.

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Question 5:

Which of the following is soluble in water?
(a) Chalk
(b) Sugar
(c) Sand
(d) Wood

Answer:

(b) Sugar

Chalk, sand and wood can be filtered from water through filtration, but sugar cannot be filtered. Sugar is soluble in water and dissolves in it.

Page No 46:

Question 1:

Fill in the blanks with the correct words.
1. The particles of the insoluble solid should be .................. (bigger/smaller) than the holes in the filtering device.
2. Chalk and sand are .................. (soluble/insoluble) in water.
3. The substance in which the solute dissolves is called a .................. (solution/solvent).
4. The quantity of a substance that can dissolve in .................. (hot/cold) water is much more as compared to .................. (hot/cold) water.
5. Sugar in the .................. (powdered/solid) form dissolves first.

Answer:

1. The particles of the insoluble solid should be bigger than the holes in the filtering device.

(This is because the particles of the insoluble solid would remain in the filtering device if they are bigger than the holes of the filtering device, and the filtered substance will pass through the holes and get separated.)

2. Chalk and sand are insoluble in water.

(Chalk and sand are insoluble in water and can be separated by filtration.)

3. The substance in which the solute dissolves is called a solvent.

(A solute dissolves in a solvent to give a solution.)

4. The quantity of a substance that can dissolve in hot water is much more as compared to the quantity of the substance that can dissolve in cold water.

(Heating water increases the solubility of a solute in it.)

5. Sugar in the powdered form dissolves first.

(A powdered solute is more soluble than the solute in the crystal form.)



Page No 47:

Question 1:

Name the different methods of separation.

Answer:

The various methods of separation are as follows.

  1. Threshing: This process is used to separate grains or seeds from the stalk by beating the crops on hard surface or with the help of machines.
  2. Winnowing: It is the process used to separate grains from chaff by blowing air through them or by allowing the wind to blow through them.
  3. Hand-picking: When a small number of impure particles are present in a small quantity of a mixture, and the impure particles are distinguishable from the useful substance, they can be separated by hand-picking.
  4. Sieving: Small substances pass through the pores of a sieve, but large impurities remain in the sieve. Thus, the difference in the sizes of the impurities and the useful material helps in this method of separation known as sieving.
  5. Sedimentation and decantation: Separating insoluble solids suspended in a liquid by settling them is called sedimentation. After sedimentation is complete, the upper liquid, which is pure, is poured out without disturbing the sediment. This process is known as decantation.
  6. Filtration: In this process, an insoluble solid and a liquid in a mixture can be separated by passing the mixture through a filtering device.
  7. Evaporation and condensation: Heating a mixture of a liquid and a soluble solid changes the liquid into gas by evaporation, leaving behind the solid. The vapours of the liquid change back into the liquid state after coming in touch with a cold surface (by the process of condensation), thereby separating the soluble solid and the liquid in the original mixture.

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Question 2:

When can sieving be done?

Answer:

Sieving can be done when the components of a mixture are of different sizes. The smaller size particles pass through the pores of the sieve and the larger components remains in the sieve. This method is used in homes to separate wheat bran from flour and in construction sites to separate stones and pebbles from sand.

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Question 3:

Why is it not advisable to sieve wheat flour?

Answer:

It is not advisable to sieve wheat flour because, on sieving, wheat bran, which is rich in nutrients and fibre, is removed. It is better to hand-pick and remove the impurities.

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Question 4:

Differentiate between sedimentation and decantation.

Answer:

Sedimentation Decantation
Sedimentation is the process by which insoluble solids suspended in a liquid are separated by allowing them to settle. Decantation is the process of pouring out the clear upper liquid from a solution without disturbing the sediments.

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Question 5:

What is filtration? Give two common examples of filtration.

Answer:

Filtration is the process of separating insoluble solid impurities from a liquid by passing it through a filtering device. Insoluble solid particles are retained in the filtering device but the liquid passes through it.
Examples: Filtration of tea leaves after preparation of tea using a strainer, and filtration of water to remove solid impurities.

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Question 6:

How is a solute different from the solvent? Give two examples of a common solute.

Answer:

A solute is the substance that dissolves, and a solvent is the substance in which the solute dissolves to form a solution. Examples of two common solutes are salt and sugar, which dissolve in water.

Page No 47:

Question 1:

What is threshing? Explain the ways in which threshing is commonly done.

Answer:

The process of beating harvested crops to separate the grains from the stalks (the dried stems) is called threshing. Threshing is of two types: manual threshing and threshing using machines.
Manual threshing is done by holding a bundle of crops and beating it on a hard surface. This process loosens and separates the grains from the stalk. Sometimes, threshing is also done by crushing stalks under the feet of bullocks.

Threshing can also be done by using machines such as the combine harvester.

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Question 2:

What is winnowing? How is it done?

Answer:

Threshed grains may still contain seed coverings and tiny pieces of leaves or stem collectively called chaff, which is removed by winnowing. Winnowing is a method by which chaff is removed from the grains by blowing air or wind through them.
In winnowing, the grain and chaff mixture is taken in a winnowing basket. The mixture is allowed to fall to the ground from a height. The chaff, being lighter than the grains, is easily carried away by the wind, allowing the chaff to form a separate heap from the grains. In this process, the direction of the wind plays an important role.

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Question 3:

What is hand picking? When is this method used?

Answer:

Hand-picking is a method of separation by which impurities that are different from the useful material in a mixture are hand-picked and removed. For example, rice, wheat, pulses, etc., contain impurities such as small stones or unwanted grains. These impurities look different from the useful material and are easily hand-picked and removed.
This method is used when these following conditions are fulfilled.

  1. The quantity of the mixture is small.
  2. The unwanted material is present in smaller quantities.
  3. The size, shape and colour of the impurities are different from those of the useful substance.

Page No 47:

Question 4:

Define saturated solution. How would you prepare a saturated solution of sugar in water?

Answer:

A saturated solution is a solution in which no more of the solute can be dissolved.
A saturated solution of sugar in water can be prepared by continuously adding spoonfuls of sugar to water and stirring the solution each time to dissolve the sugar crystals. After some time, some grains of the sugar will be left at the bottom and does not dissolve in the water even after stirring. This solution is called a saturated solution of sugar.

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Question 5:

How can the solubility of a substance be increased?

Answer:

The solubility of a solute can be increased by the following ways:

  1. Heating: The solubility of a solute increases on heating the solution. For example, more sugar can be dissolved in hot water than in cold water.
  2. Stirring: Stirring will dissolve more solute in a solvent. Here is an example. Add sugar to water in two glasses. Letting one solution remain undisturbed, stir the other. More sugar dissolves in the glass that is stirred.
  3. Solute in powdered form: Powdered solute dissolves more than the solute in crystal form. For example, crushed sugar dissolves more in water than sugar cubes.



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