5. SEPARATION OF SUBSTANCES

 

SOME IMPORTANT QUESTIONS

 

Q. 1. What is a mixture ?

Ans. A substance which is made of two or more kinds of particles (molecules) of different substances in such a way that the particles can be separated by physical means is called a mixture.

 

Q. 2. Give five examples of mixtures ?
Ans.
(1) A glass of neembu-pani is a mixture of water, sugar and citric acid.
(2) Smoke is a mixture of carbon particles and air.
(3) Sea water is a mixture of water and a large number of salts of metals.
(4) Air is a mixture of oxygen, nitrogen, carbon dioxide and water vapour.
(5) Vinegar is a mixture of acetic acid and water.

 

Q. 3. What is the need of separation of the components of a mixture ?

Ans. We carry out the separation of the components for the following purposes :
(a) To remove the unuseful or harmful component.
(b) To remove impurities for getting a pure sample, and
(c) To obtain the useful component.

 

Q. 4. What is the name of the method used to separate butter from milk ?

Ans. Centrifugation or churning method.

 

Q. 5. Give two properties of mixtures.

Ans. (i) The ratio of their constituents is not fixed.
(ii) Mixtures do not have definite melting point or boiling point.

 

Q. 6. What do you mean by winnowing ?

Ans. It is the process of separation of grains from husk and hay with the help of wind.

 

Q. 7. Name the harmful components in the following mixtures.
(i) Argemone oil and mustard oil, (ii) A mixture of Kesri and Arhar dal.

Ans. (i) Argemone oil, (ii) Kesri

 

Q. 8. Name the components in the following mixtures.
Petroleum and brass.

Ans. Petroleum—Petrol, kerosene and diesel oil.
Brass—Copper and Zinc.

 

Q. 9. What do you mean by evaporation ?

Ans. The process of removing water or moisture from a mixture either by heating on flame or by direct sunlight is called evaporation, e.g., salt from sea water is obtained by this method.

 

Q. 10. State whether the following statements are True or False ?
(1) A mixture of milk and water can be separated by filtration.
(2) A mixture of powdered salt and sugar can be separated by process of winnowing.
(3) Separation of sugar from tea can be done with diltration.
(4) Grain and husk can be separated with the process of decantation.

Ans. (1) False (2) True (If sugar particles larger in size)
(3) False (4) False.

 

Q. 11. Fill up the blanks :
(1) The method of separating seeds of paddy from its stalks is called ................... .
(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 ................... .
(3) Salt is obtained from sea water by the process of ................... .
(4) 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. (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 sea water by the process of evaporation .
(4) 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.

 

Q. 12. When is handpicking done ?

Ans. Handpicking is usually done to separate undesirable substances like small pebbles, dirt from wheat, rice and pulses. This method is used to remove unwanted particles, when the components of a mixture are different in colour, size and shape. However, it can be done only when one of the components is present in small quantities.

 

Q. 13. What is magnetic separation ?

Ans. The process of separating a magnetic substance from a non-magnetic substance, by using a magnet is called magnetic separation. For example, in industries, impurities of iron can be removed from several substances by using a magnet. In many big industrial units, scrap iron is separated from the heat of waste materials by using big electromagnets fitted to a crane.

 

Q. 14. How will you separate a mixture of iron fillings and sulphur ?

Ans. A mixture of iron fillings and sulphur can be separated by magnetic separation. For this first of all spread the mixture on a plane sheet of paper. Take a magnet and move it through the mixture till the whole of iron fillings are attracted by the magnet. Remove the iron fillings from the magnet and keep them separately. Sulphur powder is left beind on the sheet of paper. Thus, the component of the mixture is separated.

 

Q. 15. State how one cane separate a mixture of iodine and sand.

Ans. First of all, take mixture of iodine and sand in a china dish and put an inverted funnel over the dish. Now, insert some cotton in the funnel over the mixture and heat until the funnel is filled with violet vapours completely. Cool the funnel. The violet vapours will solidify on the inner wall of the funnel. The sand will be left on the dish as a residue. Thus the components of the mixture are separated.

 

Q. 16. How can the solids which ae insoluble in water and are heavier than the other components of the mixture be separated ?

Ans. Solids which are insoluble in water and are heavier than the other components of the mixture can be separated by sedimentation followed by decantation.
Sedimentation— It is the process of settling down of heavier insoluble particles in a mixture of water and insoluble substances.
Decantation—The process of transferring the clear liquid (after sedimentation) without disturbing the sediment (insoluble heavy particles).

 

Q. 17. What is loading ?

Ans. The process of increasing the rate of sedimentation in a suspension by adding some chemical to it is called loading.

 

Q. 18. How will you separate a mixture of iron filings, sand and common salt ?

Ans. Spread the mixture on a sheet of paper and roll in it a powerful horse shoe magnet. Remove the magnet from the mixture and scrape off the iron filings from it. Repeat the procedure till no iron filings are left in the mixture.
Now dissolve the mixture in 100 ml of water. The salt will dissolve, but not the sand. Filter the mixture. The sand is left on the filter paper, and the clear common salt solution collects as a filtrate. Wash the sand with distilled water so as to remove any traces of salt. Dry the sand in hot air.
Transfer the filtrate into a china dish and heat it over the Bunsen flame. In a few minutes, water evaporates, leaving behind dry common salt.
Thus we are able to separate the three components of the mixture.

 

Q. 19. Enlist the various common methods of separation.

Ans. The common methods employed for separation are :
(i) Hand picking (ii) winnowing
(iii) Magnetic separation (iv) Sieving
(v) Sedimentation (vi) Decantation
(vii) Evaporation (viii) Filteration
(ix) Loading (x) Distillation
(xi) Sublimation (xii) Churning.

 

Q. 20. What is sieving ?

Ans. This method is used to separate the components of a mixture which are of different sizes, e.g., undesirable materials are separated from the grain by using a sieve (chhanani in Hindi). The fine particles pass through the sieve while bigger particles remain on the sieve. This method is also employed when wheat flour is passed through the sieve so as to remove the chaff.

 

Q. 21. 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 what flour, sieving allows the fine flour particles to pass through the tiny holes of the sieve, while the sugar particles remain on the sieve.