STD-6, CHAPTER - 4: SEPARATION OF SUBSTANCES, EXERCISE QUESTION ANSWERS

A.     FILL IN THE BLANKS.

1.      Housewives sometimes use the method of ______ to remove unwanted substances from eatables like rice and pulses.

Ans: handpicking

2.      Common salt is prepared on a large scale through the process of _____.

Ans: evaporation

3.      Separation of tea leaves from tea is done by a process called ______

Ans: Filtration

4.      The process of ______ can be used to increase the rate of sedimentation of the suspended particles in a solid-liquid mixture.

Ans: loading

5.      The method, used to separate the fine particles, suspended in a liquid, by rotating the mixture at high speed, is known as _____

Ans: Centrifugation

B.      MATCH THE FOLLOWING:

 

1.      Wind                                                           a. hand picking

2.      Chalk powder and water                        b. winnowing

3.      Oil and water                                            c. sedimentation

4.      Separating peas from cooked Pulao    d. filtration

5.      Muslin Cloth                                             e. separating funnel

6.      Camphor and Salt                                    f. sublimation

      Ans:

1.      Wind                                                           b. winnowing

2.      Chalk powder and water                        c. sedimentation

3.      Oil and water                                            e. separating funnel

4.      Separating peas from cooked Pulao    a. handpicking

5.      Muslin Cloth                                              d. filtration

6.      Camphor and Salt                                     f. sublimation

 

C.      TICK THE CORRECT OPTION.

 

1.      Which of the following is an example of a heterogeneous mixture?

(a)    Sugar in water       (b) Pebbles in rice          (c) an aerated drink        (d) salt in water

      Ans: pebbles in rice

2.      Which one of the following is not an example of a pure substance?

(a)    oxygen             (b) air         (c) copper          (d) carbon dioxide

      Ans: air

3.      The process of loading helps to-  

(a)   Slow down the rate of sedimentation

(b)   Speed up the rate of sedimentation

(c)    Speed up the rate of decantation

(d)   Slow down the rate of decantation       

       Ans: speed up the rate of sedimentation

4.      Transferring the clear liquid, into another container, leaving behind the residue, is called–

(a)    sedimentation                                  (b)  decantation

(c)    Condensation                                    (d)   crystallisation

      Ans: decantation

5.      A substance, that sublimes easily, is-

(a)   naphthalene                                     

(b)   salt

(c)    sugar

(d)   chalk

      Ans: Naphthalene

D.     ANSWER THE FOLLOWING QUESTIONS IN BRIEF.

 

1.      Name any three methods used for separating a solid-solid mixture.

Ans: Three methods used for separating a solid-solid mixture are, sieving, threshing, sublimation.

2.      What is winnowing? Give an example of a mixture whose components can be separated by this method.

Ans: Winnowing is a process in which lighter substance are separated from heavier substances with the help of wind energy. The lighter husk are separated from the heavier wheat grains by the process of winnowing.

3.      Some iron pins get scattered on the carpet when you are expecting guests. How can one collect all the pins in the shortest possible time?

Ans: By using a magnet we can take out the iron pins quickly.

4.      Name any three substances which sublime on heating.

Ans: Three substances that sublime on heating are, ammonium chloride, camphor and iodine.

5.      What is crystallisation? Name any three substances which can be purified using this technique.

Ans: Crystallisation is a process which separates a pure solid, in the form of its crystals, from a saturated solution. Salt, sugar and washing soda can be purified using this technique.

E.      ANSWER THE FOLLOWING QUESTIONS.

 

1.      Differentiate between a pure substance and a mixture. Give two examples of each.

Ans: Pure Substance: A substance consisting of only one kind of particles is called a pure substance. Ex- Oxygen, Copper

Mixture: Mixture consists of two, or more, substances mixed together in any proportion. Ex- milk, air

2.      State the difference between heterogeneous and homogeneous mixtures

Ans: Heterogeneous Mixture: A mixture, having different compositions, over its different parts is called as heterogeneous mixture.

Examples: mixture of sand in water, iron nails in sulphur powder

Homogeneous Mixture: A mixture, having the same composition, over all its parts is called as homogeneous mixture.

Examples: Alloys, soft drinks

3.      Can a mixture of iodine and camphor be separated by the sublimation method? Give reason for your answer.

Ans: i) Sublimation is a method to separate solids, which sublime (changes to gaseous form) easily from substances which do not sublime.

ii) In this case, iodine and camphor both will sublime on heating. So, it is not possible to separate these two by the process of sublimation.

4.      Why does the size of naphthalene balls, put in open, keep on reducing with time?

Ans: i) We know that, naphthalene sublimes (changes directly into gaseous form).

ii) When naphthalene balls are kept in open, they continue to absorb the heat from the surrounding and sublime. So, their size goes on reducing with time.

5.      After a dust storm, how does rain help in making air clear?

Ans: i) In a storm, the dust particles being lighter in weight float in the air, and we cannot see anything around us.

ii) After this, if rain occurs, the dust particles along with the water droplets become heavy and come down to earth surface. Thus the atmosphere becomes clear.

6.      Sawdust, mixed in water, cannot be separated by the sedimentation method. Why?

Ans: i) Sedimentation is a process in which substances mixed in water settle down (sink in it) after some time.

ii) But as sawdust is lighter in weight, it will float on the surface of water and will not settle down. So it is not possible to separate sawdust, mixed in water by the process of sedimentation.

7.      The filtration method cannot be used to separate sugar and salt mixed in water. Why?

Ans: i) Filtration is done to separate the insoluble solids mixed in water with the help of cotton cloth or filter paper.

ii) But as sugar and salt are soluble in water, they pass through the filter paper (or cotton cloth) and thus cannot be separated through the process of filtration.

8.      Describe the method of centrifugation using an appropriate example.

Ans: Centrifugation is used to separate the fine particles suspended in a liquid, by rotating the mixture at high speeds.

       Take the example of separating cream from milk. In this process the milk is churned (rotated at a high speed). The heavier particles (cream) tend to settle down at the bottom of the container while the lighter ones stay at the top.