Separation of Substances (part -3) class 6

Separation of Substances


Q.11. Write a short note on each:
           Evaporation and condensation
Ans. 
Evaporation
  • Evaporation is the process in which a liquid gets converted into its vapour. 
  • Evaporation can be used to separate a solid dissolved in a liquid.
  • The process of evaporation takes place continuously wherever water is present.
  • For example: 
    • Steam rises from wet clothes while they are ironed.
    • Blackboard dries up after wiping it.
    • The process of evaporation is used to separate a mixture of water and salt.
Condensation
  • The process of conversion of liquid vapour into its liquid form is called condensation.
  • For example:
    • Water drops appear on the outer surface of a glass containing cold water. 
    • We see water drops condensed under a plate that has been used to cover a vessel containing milk that has just been boiled.
Q.12. How do we get salt from sea water?
Ans. Sea water contains many salts mixed in it. One of these salts is the common salt.
  • When sea water is allowed to stand in shallow pits, water gets heated by sunlight and slowly turns into water vapour, through evaporation.
  • In a few days, the water evaporates completely leaving behind the solid salts. Common salt is then obtained from this mixture of salts by further purification.
Q.13. You are given a mixture of sand, salt and iron filling. How will you separate all these components?
Ans. A mixture of sand, salt and iron filling can be separated as following:
  • A strong magnet is moved through the mixture to attract iron filling.
  • Remaining mixture of sand and salt is put in water to get dissolved.
  • Sand will not dissolve and will settle down due to sedimentation but salt will dissolve in water.
  • Now we can separate salty water from sand by decantation or filtration.
  • Now salt can be separated from water by evaporation and water loss due to evaporation can be conserved by condensation of water vapours.
Q.14. How will you separate husk or dirt particles from a given sample of pulses before cooking?
Ans. We can wash the pulses with water. Pulses are heavier than husk or dirt. So by sedimentation, Pulses will settle down while husk or dirt will come up in water.
Now, we can separate this polluted water from pulses by decantation.

Q.15. What are saturated and unsaturated solutions?
Ans. A solution is said to be saturated if it cannot dissolve more of the substance into it. For example, adding more and more salt in water will lead to a condition when no further salt will get dissolve in water and settles at the bottom of the beaker.
On the other hand, A solution is said to be unsaturated if it can dissolve more of the substance into it. 

Q.16. How does solubility of a liquid get affected by temperature? 
Ans. The solubility of a liquid increases with increase in temperature and decreases with decrease in temperature.
That means, More of a substance can be dissolved in a solution by heating it.

Q.17. Does water dissolve equal amounts of different soluble substances?
Ans. No, Water dissolves different amount of soluble substances in it.

Q.18. 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?
Ans. We should add ice at last because ice will make it cool by decreasing the temperature of water. So, the solubility of water to dissolve sugar and lemon will also decrease. Hence, it will take long time and efforts to dissolve it.



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