SEPARATION OF SUBSTANCES
                                      Separation of Substances


1.    Pure substances : Many substances around us contain only one type of constituent particles. Elements and compounds are pure substances. These are called pure substances. For example, iron, copper, water, salt, etc.

2.    Impure substances :Substances containing more than one type of constituent particles are called impure substances for example, pond water, milk, etc.

3.   
Impurities : These are the unwanted particles present in a substance making it impure.

4.   
Mixtures :Substances which contain more than one component mixed in any ratio are called mixtures. For examples : air is a mixture of many gases like Nitrogen, Oxygen, Carbon dioxide and dust particles, etc.

5.   
Homogeneous mixtures :Mixture in which the particles of the substance present cannot be seen are called homogeneous mixtures. For example, solution of sugar and water, air, cold drinks.

6.   
Heterogeneous mixtures : Mixture in which particles of the substances present can be seen easily are called heterogeneous mixtures. For example, water in oil, dust in air.

7.   
Solution : When a soluble substance is dissolved completely in a liquid (say sugar in water). A homogeneous mixture is formed. It is known as solution.

8.   
Saturated solution : A solution in which no more soluble substance can be dissolved at room temperature is called saturated solution.

9.   
Need for separation : We carry out the separation of the components of a mixture or an impure substance with the following purposes :
(i)            To remove the unuseful or harmful component.
(ii)          To obtain the useful component.
(iii)         To remove impurities for getting a pure sample.

10.
Principle of separation
1.    The substances present in a mixture retain their original properties like particle size, density, melting point, boiling point, volatility, etc.
2.    We use the difference in anyone of these properties in the components of a mixture to separate them.

11.
Methods of separation : Hand picking, winnowing, sieving, magnetic separation, sedimentation, decantation, loading, filtration, evaporation, sublimation, distillation, churning, etc. are some common methods of separation.

12.
Handpicking :This method is used for separating small particles of dirt, stone, husk etc. from the grains of wheat, rice, pulses, etc.

13.
Sieving
(i)            Sieving is used when two component of a mixture have different particle size.
(ii)          Sieving allows the fine particles to pass through the holes of the sieve, while the bigger particles remain on the sieve. For examples, sieving of wheat flour, sieving of sand at construction sites.

14.
Winnowing : Winnowing can be used to separate lighter and heavier components of a mixture. For example : to separate husk from grain with the help of air.

15.
Threshing : The process that is used to separate grain from stalks is threshing.

16.
Decantation :It is the transfer of clean liquid from one vessel to other vessel without disturbing the settled (sedimented) particles.

17.
Loading : It is the process of faster sedimentation by suspending alum to a liquid.

18.
Filtration :Filtration is used to separate solid particles from liquid by passing the mixture through a filter paper.

19.
Evaporation :It is the process of removing water (or moisture) from a mixture either by heating on flame or direct sunlight. For example : salt from sea water is obtained by this method.

20.
Condensation :The process of conversion of water vapour into its liquid form is called condensation.

21.
Churning (or centrifugation) :It is the process of separation of the lighter particles of a suspended solid from a liquid. For example : to obtain butter from the curd or milk.

22.
Crystallisation :The process of crystallization is used for obtaining pure crystallive substance from impure sample.

23.
Sedimentation :It is the process of settling of heavy solid particles in a mixture at the bottom of the vessel.
 

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

Ans.
We carry out the separation of substances for the following purposes :
1.    To remove the unuseful or harmful component : For example, removing tea leaves after making tea.
2.    To obtain the useful component :For example, getting wheat, rice grains after separating husk, dirt etc.
3.    To remove impurities for getting a pure sample :For example, obtaining sugar crystals from jiggery (gur) or salt from sea water.

Q.2. What is winnowing ? Where is it used ?


Ans.
Winnowing is the process of separating wheat or rice grains from the husk. Wheat grains and husk are different in weight, husk being lighter than wheat. When the mixture is allowed to fall down from a height the wind carries the lighter husk with it and the heavy wheat grains fall vertically down on the ground.
 



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

Ans.
Husk or dirt particles from pulses can be separated by hand picking method.

Q.4. What is sieving? Where is it used?

Ans. Sieving is the method to separate particles of different sizes. Undesirable particles can be separated from grains by this method. The size of holes in the sieves depends upon the size of the particles. In cashewnut factories, the cashewnuts of different sizes are separated, by sieving. Jewellers also separate pearls of different sizes by this method.

Sieving flour before consuming is not a good practice. We should consume it along with the husk because husk provides roughage which is useful for our body in proper bowel movement.

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


Ans.
Take a beaker (100 ml) half filled with given sample of water. Stir the water thoroughly. Now keep the beaker undisturbed for sometime. Sand gets settled down at the bottom of the beaker. After sometime water can be separated by decantation process and sand is left in beaker.


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


Ans.
Yes, We can separate sugar from wheat flour by sieving. In the mixture of sugar and wheat flour, sieving allows the fine flour particles to pass through the holes of the sieve, while the sugar particles remain on the sieve.

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

Ans.
We can purify the muddy water by loading. Firstly, we take a beaker (100 ml) half filled with muddy water. Now take a piece of alum (phitkari) and a thread (about 30 cm in length). Tie firmly one end of the thread with alum and hold the other end of the thread with hand.
Now dip the alum in the water and move it slowly in a circular path for about one minute. Remove the alum and keep the beaker undisturbed for some time. During this process we will find that the dust particles get loaded and become heavier and settle down, the water becomes clear. The clear water is then decanted into another beaker.

Q.8. Fill up the blanks :


a)   
The method of separating seeds of paddy from its stalks is called ……… .
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 ………… .
c)    Salt is obtained from seawater by the process of ………. .
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 ……….. .

Ans.
a) threshing
         b) filtration
         c) evaporation
         d) decantation


Q.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.

Ans.
a) False
         b) False
         c) False
         d) False

Q.10. Lemonade is prepared by mixing lemon juice and sugar in water. You with to add ice to cool it. Should you add ice to the lemonade before or after dissolving sugar? In which it be possible to dissolve more sugar?


Ans.
We should add ice to lemonade after dissolving sugar. Without ice, sugar dissolves easily in lemon juice, because solubility depends on the temperature. If sugar is added to ice-cold solution of sugar and lemon juice, the solubility of sugar will be decreased.
 
IMPORTANT QUESTIONS

Q.1. Which type of separation is used in cashew-nut factories?


Ans.
Sieving.

Q.2. Name three mixture commonly found in nature.


Ans.
Three natural type of mixtures are milk, sea water and jiggery (Gur).

Q.3. Name the method by which you can separate butter from milk.


Ans.
Centrifugation.

Q.4. Name some materials that are used as filters.


Ans.
Cotton, ceramic, filter cloth, filter paper.

Q.5. Name the process of separating two immiscible liquids.


Ans.
By using separating funnel or by decantation.

Q.6. Which substance is used for loading?


Ans.
Alum.

Q.7. What is the use of alum in loading?


Ans.
Alum is used to make the sedimentation faster. By adding alum the clay particles settle down rapidly.

Q.8. During centrifugation, which particles settle down at the bottom?


Ans.
Heavy particles settle down at the bottom and lighter particles float at the top of the liquid.

Q.9. Which process is used to separate bacteria from water?


Ans.
Filtration, by using special filters.

Q.10. What is the drawback of evaporation?


Ans.
The liquid in the mixture is evaporated off into the air and is not recovered.

Q.11. Name the process to obtain salt from sea water.


Ans.
Evaporation.

Q.12. Which type of mixtures are separated by evaporation?


Ans.
Evaporation is used to separate solids dissolved in liquid.

Q.13. Name the device by which cream can be separated
from milk at home.

Ans.
A mixer-grinder is the very important device by which cream can be separated from milk.

Q.14. Give one example of sieving used in everyday life.

Ans.
Separation of barn (choker) from flour.

Q.15. When hand-picking is used?


Ans.
Hand-picking is used to separate undesirable component, when present in small amount.

Q.16. What is a mixture? Give two examples of a mixture.

Ans.
A mixture is a substance which is made up of two or more components mixed in any ratio, example : soil, air, etc.

Q.17. Name two pure substance that you know.


Ans.
Silver, sodium chloride are pure substances.

Q.18. Mention
the harmful components present in the following mixtures:
(i)    Water from an abandoned well.
(ii)  Argemone oil and mustard oil.

Ans.
(i)Small insects and rotten leaves.
         (ii)Argemone oil.

Q.19. Why does visibility increase after rains?


Ans.
After rains, the objects at a distance are seen more clearly, because the fine dust particles that are present in air settle down due to loading by rain drops.

Q.20. Describe the method to obtain pure salt from rock salt.


Ans.
First the mixture is crushed and grinded. Water is then added and filtered. Pure salt is collected as filtrate which is heated. Water evaporates off and pure salt is left.

Q.21. How will you separate pure water from a solution of salt in water?


Ans.
We can separate pure water from a solution of salt in water, by the process of distillation that is by evaporation followed by condensation.

Q.22. What is the use of decantation?


Ans.
Decantation is used to separate insoluble solids from liquids. Two immiscible liquids are also separated by this process.

Q.23. What is strainer?


Ans.
 Wire mesh is commonly known as strainer. For example, while preparing tea, we separate tea leaves from water by using a filter such as wire mesh. Tea leaves are bigger in size than the holes of the mesh.


Q.24. How will you separate a mixture of common salt and chalk powder?


Ans.
We know that common salt is soluble in water while chalk is sparingly soluble. So on the basis of different solubility, we can separate the common salt and chalk powder as follows :
(i)    Firstly, some water is mixed with the mixture of common salt and chalk powder, stir the solution well. Filter the solution by using filter paper. On filtering, chalk powder is obtained as a residue on the filter paper and salt solution is obtained.
(ii)  Now filtrate is evaporated and dry common salt is left behind.

Q.25. What is threshing? How is it done?


Ans.
The process that is used to separate grain from stalks is threshing. In this process, the stalks are beaten to free the grain seeds . Sometimes, threshing is done with the help of bullocks. Machines are also used to thresh large quantities of grain.

Q.26. In the following list classify the substances into pure substance and mixtures.
Wheat with small stones, milk, rice with insects, tea leaves in water, rocks, sugar, distilled water, tap water.

Ans.
(i)Pure substances : Sugar and distilled water.
         (ii)Mixtures : Wheat with small pieces of stones, milk, rice with insects, tea leaves
              in water, rocks and tap water.
Q.27. Name two commonly known mixtures, the components of which are useful after separation.

Ans.
Two such mixtures are milk and sugarcane juice.
(i)    Milk can be separated into cream which is a useful thing. It can be used as fat. The remaining mixture is also useful.
(ii)  Jaggery is a component of sugarcane juice, which is a useful thing.

Q.28. Distinguish between pure and impure substances.


Ans.

Pure SubstancesImpure Substances
 
1.    They contain one or more type of particles combined in fixed ratio.
 
2.    They have fixed melting and boiling points.
 
3.    They are homogeneous.
 
 
4.    They have specific colour and taste.
1.    They contain more than one type of particles combined in any ratio.
 
2.    They do not have melting and boiling points.
 
3.    They may or may not be homogeneous.
 
4.    They do not have specific colour and taste.
 
Q.29. What is decantation?
Ans. Decantation is a process of separating insoluble solids from liquids. A suspension of solid particles in liquid is allowed to stand for sometime. Solid particles settle down at the bottom, due to their weight. This is called sedimentation. The clean water is transferred into another beaker, without disturbing the settled particles. This type of separation is called decantation. 

 

Q.30. What is the importance of centrifugation? How it is done?


Ans.
Centrifugation is the process of separating suspended particles from a liquid by rotating the liquid at a high speed.
The mixture is taken in a closed bottle and rotated at a high speed. The heavy particles settle at the bottom while light particles remain behind. This method is used to separate cream from milk. Cream collects at the centre and being lighter than milk, it floats at the top of the mixture.

 

Q.31. What is filtration?

Ans.
When one component of a mixture is soluble in water and other component is insoluble in water, the soluble component gets dissolved and insoluble one is separated by filtering the solution.
The process by which insoluble substance can be separated from a solution, by passing that solution through a porous paper (filter paper) is called filtration. During filtration, the solid insoluble substance is retained at the filter paper as residue while the liquid free from any suspended matter passes through the filter paper and is collected as filtrate. This filtrate may be warm to dry to obtain soluble component. 


 

Q.32. Name the property of the components used for separating the following mixtures :


(i)   
salt and camphor
(ii)  wheat and husk
(iii)magnetic separation
(iv)separating funnel

Ans.
(i)sublimation
        (ii)winnowing
        (iii)magnetic separation
        (iv) separating funnel

Q.33. How is common salt obtained from sea water?


Ans.
When sea water is allowed to stand in shallow pits, water gets heated by sunlight and changes into water vapour by the process of evaporation leaving behind impure solid salts. Now, the lumps of impure common salt are crushed to get powdered salt. The powdered common salt is dissolved in water to prepare a solution. Now the solution of common salt is filtered to remove insoluble impurities. The clear solution is evaporated by heating to remove the water content to obtain a concentrated solution of common salt. The hot and concentrated solution is allowed to cool. On cooling, crystallization takes place and crystals of pure common salt are obtained.


Q.34. Mention the methods that can be used for the separation of the following mixtures :

(i)   
wheat, sugar and husk
(ii)  rice, gram and iron fillings
(iii)sand, black gram (urad) and husk

Ans.


(i)    Mixture of wheat, sugar and husk.
1.    For separating husk from the mixture, we should follow the winnowing method as husk is lighter than other two components.
2.    Wheat and sugar can be separated by sieving as they have different sizes.
(ii)  Mixture of rice, gram and iron fillings.
1.    For separating iron fillings, we can use a magnet.
2.    Rice and gram can be separated either by sieving or by hand-picking.
(iii)Sand, black gram (urad) and husk.
1.    For separating sand from the mixture, we can sieve the mixture.
2.    Black gram (urad) and husk can be separated by the method of winnowing.

Q.35. Write down the various components of the mixtures given in Table 1.


Table 1 : Components of Some Mixtures

S.No.MixtureComponents
 
1.
 
Sharbat 
2.
 
Rock salt 
3.
 
Wheat from field 
4.
 
Soft drink 
5.
 
Tap water 
 

Ans.

S.No.MixtureComponents
 
1.
 
SharbatWater, sugar, coloured and flavouring substances.
2.
 
Rock saltSome salts, soil and sand.
3.
 
Wheat from fieldDust particles, husk, insects, small pieces of stones, stem.
4.
 
Soft drinkCarbonated water, sugar, citric acid, flavours.
5.
 
Tap waterMixture of many salts, sand and clay particles.
 

Q.36. Name the components in the following mixtures :

          Pond water, milk, sugarcane juice, soil.

Ans.
Mixtures is an impure substance. It may contain many things. Various components of the following mixtures are :
(i)  Pond water : Pond water is a mixture of sand, clay, water and various impurities (salt of sodium, calcium or potassium).
(ii)Milk : Milk is a mixture of water, milk protein (casein), fat etc.
(iii)Sugarcane juice : Sugarcane juice is a mixture of sugar, water and many other substances.
(iv)   Soil : Soil is a mixture of sand, clay, various salts and remains of the plants and animals.

Q.37. Complete Table 2.


Table 2 : Separation of Mixtures

S.No.MixtureComponentsUnwanted/Harmful
Component, if any
1.Ice-cream
 
  
2.
 
Wheat (as obtained from field)  
3.
 
Lemon squash  
4.
 
Cooked vegetables  
 
Ans.
S.No.MixtureComponentsUnwanted/Harmful
Component, if any
1.Ice-cream
 
Milk, sugar, creamNil
2.
 
Wheat (as obtained from field)Wheat grain, husk, small pieces of stone
 
Small pieces of stone, husk
3.
 
Lemon squashLemon, sugar, waterNil
4.
 
Cooked vegetablesMixed vegetable, oil, spicesNil
 
Q.38. How will you separate a mixture of milk and cooking oil?

Ans. Firstly, we take about 25 ml of cooking oil and about 25 ml of milk and mix them together in beaker (100ml). Stir the liquid with a glass rod. After sometime, we observe that cooking oil forms a separate layer above milk. Separate the upper layer of the liquid by decantation process. Immiscible liquid can also be separated by a separating funnel.
Separation of milk and cooking oil can also be separated by using a separating funnel. In separating funnel add both milk and cooking oil. Now, on carefully opening the stop cock of the separating funnel, milk can be separated and collected in the beaker kept below the funnel.

Q.39. What is the basis for choosing the method of separating the components of a mixture?


Ans.
The basis for choosing the method of separating the components of a mixture depends upon the nature and composition of the mixture.
Commonly used methods for separating the components of a mixture are hand-picking, sieving, winnowing, magnetic separation, washing, filtration, sedimentation, decantation, evaporation, distillation etc. Once the compound is purified, its purity is tested by measuring as the criteria of purity because pure compound always possesses definite value of these properties.

OBJECTIVE TYPE QUESTIONS


Q.1. Match the following items given in Column A with that in Column B.

Column AColumn B
 
(a)  Hand picking
 
(b)  Threshing
 
(c)  Winnowing
 
(d)  Sieving
 
(e)  Sedimentation
 
(f)   Evaporation
 
(g)  Condensation
 
(h)  Churning
 
(i)    Conversion of water vapours into liquids
 
(ii)  Separating bran from four
 
(iii)Separating larger size impurities
 
(iv)Separating butter from milk
 
(v)  Conversion of water into its vapours
 
(vi)Separating grains from its stalks
 
(vii)Settling of heavier components at bottom
 
(viii)  Separation by wind or by blowing air
 
Q.2. Fill in the blanks with appropriate words:
(i)          Peanuts are separated from a mixture of wheat and peanut by ………… .
(ii)        …………… is used to separate husk from wheat.
(iii)       Fine sand can be separated from longer particles is done by …………. .
(iv)       Glass is a ………… .
(v)        Compounds have ………… melting points.
(vi)       Milk has a ………… boiling point.
(vii)     Boiling point of pure water is ………… than that of impure water.
(viii)    Mixture may be solid, liquid or ………… .
(ix)       Butter is a component of ………… .
(x)        Sugarcane juice is a mixture of ……….., water and many other substances.
(xi)       Separation of components is done to obtain a ………… substance.
(xii)     Components retain their properties in a ………… .
Q.3. State whether the statements given below are True or False :
(i)          Butter is separated from butter milk by churning.
(ii)        Separation of components of a mixture is a useful process.
(iii)       Ink looses its properties when mixed in water.
(iv)       ‘Sharbat’ is a mixture of sugar and water.
(v)        Rocks are pure substances.
(vi)       Milk is a mixture.
(vii)     Common salt is a pure substance.
(viii)    Mixture has properties different from its components.
(ix)       Tap water and pond water are alike.
(x)        Elements are pure substances.
(xi)       A pure substance has a fixed melting and boiling point.
(xii)     Condensation method is used for separating substances which on heating change directly into vapour.
Q.4. Choose the correct option in the following questions:
(i)          Butter is separated from milk by
(a)sedimentation                             (b)filtration
(c)churning                                      (d)decantation
(ii)        Filtration is a method to separate the components of a
(a)solution
(b)mixture of a liquid and an insoluble substance
(c)both (a) and (b)
(d)pure substance
(iii)       Threshing is done by
(a)beating                                         (b)bullocks
(c)machines                                         (d)all these methods
(iv)       Which method is used to separate pebbles and stones from sand?
(a)Hand picking                                   (b)Winnowing
(c)Sieving                                             (d)Any of these
(v)        The components of a solution (say sugar in water) can be separated by
(a)filtration                                            (b)evaporation
(c)sedimentation                                  (d)decantation
(vi)       Sand from water is separated by
(a)sieving                                              (b)evaporation
(c)filtration                                             (d)sedimentation and decantation
(vii)     The process of conversion of water into liquid is called
    (a) condensation                                  (b)decantation   
    (c)sedimentation                                  (d)evaporation
     (viii)  The process of conversion of water into its vapours is called
   (a)evaporation                                       (b)condensation
   (c)guttation                                             (d)transpiration
     (ix)   A mixture of ammonium chloride and sand is separated by
             (a)evaporation                                         (b)decantation
             (c)sublimation                                          (d)fitration
     (x)   The property which forms the basis of sieving
            (a)difference in weight                            (b)difference in colour
            (c)difference in shape                             (d)difference in size
 
ANSWERS TO OBJECTIVE TYPE QUESTIONS
Q.1. Match the items in Column A with Column B :
Column AColumn B
 
(a)  Hand picking
 
(b)  Threshing
 
(c)  Winnowing
 
(d)  Sieving
 
(e)  Sedimentation
 
(f)   Evaporation
 
(g)  Condensation
 
(h)  Churning
(iii) Separating larger size impurities
 
(vi) Separating grains from its stalks
 
(viii) Separation by wind or by blowing air
 
(ii) Separating bran from flour
 
(vii) Settling of heavier components at bottom
 
(v) Conversion of water into its vapours
 
(i) Conversion of water vapours into liquids
 
(iv) Separating butter from milk
 
Q.2. Fill in the blanks :
       (i)hand picking                      (ii)winnowing                      (iii)sieving
       (iv)mixture                             (v)fixed                               (vi)variable
       (vii)less                                 (viii)gas                               (ix)butter milk
       (x)sugar                                (xi)pure                               (xii)mixture.
Q.3. True/False :
       (i) True                                   (ii) True                                (iii) False
       (iv) True                                 (v) False                              (vi) True 
       (vii) True                                (viii) False                            (ix)  False  
       (x) True                                  (xi) True                               (xii) False
Q.4. Choose the correct option :
(i)            (c) Butter is separated by churning.
(ii)          (b) Components of solution cannot be separated by this method.
(iii)         (d) All the three methods can be used for threshing.
(iv)         (c) Hand picking will require more time while winnowing is not fit at all.
(v)          (b) By evaporation the volatile component is evaporated which is then condensed.
(vi)         (d) It can be done by evaporation and filtration also but sedimentation and decantation is easier way.
(vii)        (a) Water vapours change into liquid is called condensation.
(viii)      (a) The conversion of water into vapours is called evaporation.
(ix)         (c) Ammonium chloride separated by sublimation process.
(x)          (d) Sieving method is used for separating solid constituents of a mixture which differ in their size.