Topic outline

    • Separation of Substances

      Q26. How can we convert a saturated solution into an unsaturated solution?

      Ans. We can convert a saturated solution into an unsaturated solution in the following ways:-

                   i.        by heating the solution

                  ii.        by adding more solvent to the solution


      Q27. How do we get salt from sea water?

      Ans. The salt can be obtained from sea by the process of evaporation.

      Sea water is collected in shallow pits and heat of the sun slowly turns water into water vapor and in few days through evaporation, the water evaporates completely leaving behind solid common salt.


      Q28. You must have often noticed that sky becomes clear after the first rain. Explain why?

      Ans. Rain drops attach themselves to dust particles suspended in air, make them heavy and bring them down to the earth that is why sky becomes clear.

      Q29. Differentiate between homogeneous and heterogeneous mixtures? Give an example of each.

      Ans. Difference between homogeneous and heterogeneous mixture

      Homogeneous mixture

      Heterogeneous mixture

      1. ‘homo’ means same

      1. ‘hetero’ means different

      2. It has uniform composition

      2. It has non uniform composition

      3. It can’t be separated physically

      3. It can be separated physically

      4. Examples of homogeneous mixtures are: salt in water, sugar in water.

      4. Examples of heterogeneous mixtures are: water and sand, oil and water.


      Q30. What should the size of the pores in a sieve depend upon?

      Ans. The size of the pores in a sieve depends upon the size of the substance to be separated and the impurities of the mixture.


      Q31. What are colloids? Give few examples of colloids that you see in your daily life.

      Ans. A colloid is mixture where at least two types of substances that are not as small as a solution and not as large as a suspension are mixed together.  Each substance retains its own properties. Examples: whipped cream, milk, butter, gelatin, jelly, muddy water, plaster, colored glass, and paper.

      Q32. What is the importance of threshing to the farmers?

      Ans. The essence of threshing is separation of a cereal grain from the shaft. Threshing is done after harvesting of the crops. This may be carried out in the field or on the farm, by hand or with the help of animals or machines.


      Q33. What is the function of candles in home water filters?

      Ans. Ceramic candle filters are simple devices made out of clay and used to filter drinking water in order to removes cloudiness, suspended materials and pathogens.

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