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Subjects /Class 6 / Science.6 / Separation of Substances

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INTRODUCTION
25 Sep 2021

Meaning of Separation

On a day-to-day basis, we are faced with various instances after we are required to separate substances from one another.

The removal of substances from a mix of two or more substances.

For Example:

  • Churning milk to obtained butter
  • Separating stones from rice and wheat.


Reasons to Separate Substances

We carry out the separation of the components of a mix or an impure substance with the

following purposes:

  • To remove the not useful or harmful component
  • To obtain the useful component
  • To remove impurities for getting a pure sample

Two Types of Substances

Pure Substance and Impure Substances

The substance which contains only one kind of particle are called Pure substances.

  • For Example: Water

The substance which contains more than one kind of particles is called Impure substances.

  • For Example: A plate of rice is mixed with some stones.

Methods of Separation

Some of the methods of separation of substances are:

  • Handpicking
  • Threshing
  • Winnowing
  • Sieving
  • Sedimentation
  • Decantation
  • Filtration
  • Evaporation

Handpicking:

  • This method is used for separating small particles of dirt, stone, husk, etc., from the grains of wheat, rice, pulses, etc.
  • It is used by people working in small industries.
  • You may have seen your mother cleaning dal or rice by using handpicking method.

Threshing:

  • Grains or seeds of plants like rice and wheat serve as sources of food.

  • The flour (atta) that's used for creating chapattis is formed from wheat grains.

  • After these crops are harvested or cut, the grains got to be separated from the stalks (the dried stems). this can be done by threshing.

  • This method is mainly used in agriculture.

Winnowing:

  • Winnowing are often used to separate lighter and heavier components of a mixture.
  • For Example: To separate husk from grain with the help of air.

Sieving:

  • Sieving may be a very simple, convenient and time-saving process.
  • In this particles of varying sizes may be separated from one another with the help of a sieve.
  • A sieve is nothing but an easy device with small pores in it which permit finer materials like flour to pass through leaving behind any impurities it would contain.

Sedimentation:

  • The process of separating insoluble solids, suspended during a liquid, by allowing them to settle down is termed sedimentation.
  • The solid particles that settle down during sedimentation are called sediments.

Decantation:

  • The process of pouring out the clear upper liquid without disturbing the sediments is termed decantation.
  • The liquid above the sediments is termed a superannuate.

Filtration:

  • The process by which two substances (an insoluble solid and a liquid) are separated by passing the mixture through a filtering device is termed filtration.
  • Filtration is usually utilized in our homes. For example, after preparing tea, we filter the tea leaves using a strainer.
  • Filtration is also done to get rid of pulp from fresh fruit juice.
  • Water may also contain solid impurities, which may be removed by filtration.

Evaporation:

  • The process during which a liquid changes into a gas is termed evaporation.


Define Condensation?

  • The process in which gas changes into liquid is termed condensation.

  • Condensation is the opposite of evaporation.

  • In nature, water vapour in the air condenses to make its liquid form, the dew.

  • Condensation takes place only if water vapour hits a chilly surface.

Solution

  • When a soluble substance is dissolved completely in a liquid (say sugar in water), a homogeneous mixture is made. it's called a solution.
  • A solution in which no more soluble substance may be dissolved at room temperature is termed saturated solution.

NCERT SOLUTIONS

1. Why do we need to separate different components of a mixture? Give two examples.

Solution:

When two or more substances are mixed together they form a combination. Components of a mixture should be separated because some components might not be useful or may spoil the useful component of the mixture.

Examples:

  • Tea leaves are separated from the liquid with a strainer, while preparing tea
  • Removal of stone pieces from wheat, rice or pulses by hand

2. What is winnowing? Where is it used?

Solution:

Winnowing are often used to separate lighter and heavier components of a mixture. This method is used by farmers to separate lighter husk particles from heavier seeds of grain.

3. How will you separate husk or dirt particles from a given sample of pulses before cooking?

Solution:

Husk and dirt particles are separated from pulses by winnowing.

 

4. What is sieving? Where is it used?

Solution:

  • Sieving may be a very simple, convenient and time-saving process through which particles of varying sizes may be separated from one another with the help of a sieve.
  • A sieve is nothing but an easy device with small pores in it which permit finer materials like flour to pass through leaving behind any impurities it would contain.
  • It is utilized in a flour mill to separate impurities like husk and stones from wheat before grinding it. It’s also used at construction sites to separate pebbles and stones from sand.

 

5. How will you separate sand and water from their mixture?

Solution:

The mixture is allowed to stand without any disturbances. Now sand settles down. Slowly pour the water into another container to get sand within the bottom.

6. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?

Solution:

Yes, it is possible to separate sugar mixed with wheat flour by the following method:

  • Mix wheat flour and in water.
  • Stir the solution to allow sugar to dissolve.
  • Now filter it.
  • After that filtrate contains sugar solution and residue will be flour.

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

Solution:

  • We use a filter paper that's fixed within the funnel.
  • Then the mixture is poured on the filter paper.
  • Mud particles being larger in size will remain on the filter paper whereas clear water will undergo it.

 

8. Fill up the blanks

 

(a) The method of separating seeds of paddy from its stalks is called threshing.

(b) 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.

(c) Salt is obtained from seawater by the process of evaporation.

(d) Impurities settled at the bottom when muddy water was kept overnight in a bucket. The clear water was then poured off from the top. The process of separation used in this example is called decantation.

9. True or false?

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

(b) A mixture of powdered salt and sugar can be separated by the process of winnowing

(c) Separation of sugar from tea can be done with filtration.

(d) Grain and husk can be separated with the process of decantation.

Solution:

a) False    b) False    c) False    d) False

10. 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?

Solution:

Ice should be added to lemonade after dissolving sugar. It’s possible to add more sugar before adding ice.

Slow and Fast Changes

Slow change:

  • Those changes which happen during a long period of time.
  • These changes take place slowly and gradually.

For Example:

  • Rusting of iron
  • germination of seeds

Fast change:

  • Those changes which occur in a very short time.
  • These changes occur very fast.

For Example:

  • Bursting a balloon
  • Burning of paper

Chemical and Physical changes

Chemical changes:

  • These are the changes within which chemical properties of a substance change, and a brand new substance is made .
  • For instance , cooking of food.

For Example:

  • Baking a chapatti
  • Burning of paper
  • Burning of candle
  • Rusting of iron

What are the Characteristics of chemical changes:

  • Properties of products are different from the properties of reactants.
  • Most of the chemical changes are irreversible.
  • These changes always lead to energy changes.

Physical changes:

  • These are the changes during which only physical property of a substance changes and no new substance is created.

For Example:

  • Tearing of paper
  • Melting of wax
  • Melting of ice
  • Crushing can

What are the Characteristics of physical changes?

  • No new substances are formed.
  • Products are similar to the reactants.
  • These changes are reversible.

Reversible and Irreversible Changes

Reversible changes:

  • These are the changes that may be reversed.

For Example:

  • Stretching of rubber
  • Melting of ice
  • Water turning into vapour
  • Inflation of baloon etc.

Irreversible changes:

  • These are the changes which can't be brought back to its original state.

For Example:

  • Burning of paper

  • Ripening of fruits

  • blooming of flowers.

Other Important Concepts

Contraction:

  • A process in which an object becomes smaller or shrinks is termed contraction.

Evaporation:

  • A process during which liquid changes into vapour is named evaporation.

Expansion:

  • A process in which an object becomes bigger in size, e.g., metals expand on heating.

Melting:

  • A process during which a solid melts to become a liquid on heating is called melting.

Melting point:

  • A constant temperature at which a solid starts melting.
  • This temperature is termed the melting point of that solid.

Freezing:

  • A process during which liquid changes into solid form is named freezing.

Force and Temperature

Force:

  • A push or a pull acting on a body which tends to vary its state of rest or motion is termed a force.

Temperature:

  • It brings changes by causing increase or decrease in temperature.

NCERT SOLUTIONS

1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

Yes, this change can be reversed.

It is a physical change where we are changing the shape of the dress.

2. You accidentally dropped your favorite toy and broke it. This is a change you did not want. Can this change be reversed?

No, this change can’t be reversed.

It is an irreversible change.

Toy is made in a factory and cannot be joined again.

3. Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.

Sl No

Change

Can be reversed Yes/No

1

The sawing of a piece of wood


2

The melting of ice candy


3

Dissolving sugar in water


4

The cooking of food


5

The ripening of a mango


6

Souring of milk


SOLUTION:

Sl No

Change

Can be reversed Yes/No

1

The sawing of a piece of wood

No

2

The melting of ice candy

Yes

3

Dissolving sugar in water

Yes

4

The cooking of food

No

5

The ripening of a mango

No

6

Souring of milk

No

 

4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?

  • If the picture is created by pencil on drawing sheet, we can erase the drawing by using an eraser, it's a reversible change.
  • But if draw a picture using the sketch pens or ink pen, then we cannot erase such picture. Thus it becomes an irreversible change.

5. Give examples to explain the difference between changes that can or cannot be reversed.

Solution:

Examples of Reversible Changes:

  • Filling glass with juice
  • Melting of Ice into water. By freezing the water we can obtain ice again.
  • Folding a paper: By unfolding it, we can undo the change.
  • Hot milk to cold milk: By boiling milk, we can make it warm.
  • Open and Close the door

Examples of Irreversible Changes:

  • Burning of paper
  • Curdling of milk
  • Bursting a balloon
  • Bud to flower
  • Cutting a wood into wood pieces
  • Ripening of fruit

6. A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilized. Can the change in POP be reversed?

  • No, the change in POP can't be reversed.
  • When water is added to POP, it undergoes a chemical change.
  • Its composition changes and is converted into another substance.

7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?

  • No, the changes which have occurred in the cement couldn't be reversed.
  • Cement sets into a hard mass on mixing with water.
  • The hard mass obtained can't be converted back to cement.
  • Therefore, it's essential to keep cement faraway from rain otherwise it'll become a hard mass which is of no use.