Separation of Substances

Q19. How will you separate husk or dirt particles from a given sample of pulses before cooking?

Ans. Husk or dirt particles from a given sample of pulses can be removed by washing the pulses with water. Being heavier, pulses will settle down in the bottom of the container whereas lighter particles will keep floating in the water. This is called sedimentation. Dirty water can be removed by the process of decantation by leaving behind pulses in the bottom of the container.

Q20. What is sieving? Where is it used?

Ans. Sieving is a simple and convenient technique of separating particles of different sizes by allowing the smaller particles to pass through the holes of a sieve leaving the bigger particle in the sieve.

Uses of sieving

                      i.        Used in homes to separate flour from impurities such as husk, stalks and small pieces of stones.

                     ii.        Used in flour mill to separate broken particles of grain from flour.

                    iii.        Used at the construction sites to separate small pieces of stones from sand.

Q21. How will you separate sand and water from their mixture?

Ans. Sand is insoluble in water. So we can use two methods to separate sand and water from the mixture.

     1.   Sedimentation & Decantation – Allow the mixture to stand undisturbed for some time. Being heavier sand settles down at the bottom of the container. This process is called sedimentation. Now slowly pour the water into another container. This process is called decantation.

     2.   Filtration – Pour water on strainer or a piece of cloth or a filter paper so that water passes through the strainer and sand remains on the strainer.

 
Q22. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?

Ans. Yes, it is possible to separate sugar mixed with wheat flour by the process of sieving. Allow the mixture to pass through the sieve. Fine particles of wheat flour passes through the holes of the sieve whereas the bigger particles of sugar would remain on the sieve.

Q23. 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 sugar before adding ice as sugar dissolves faster in warm water than in cold water. We can dissolve more sugar in case of warm water.

Q24. How would you obtain clear water from a sample of muddy water?

Ans. We can obtain clear water from a sample of muddy water in the following ways:

    1.   Sedimentation and Decantation: Allow mixture to stand still for sometimes so, that mud settles down at the bottom. This process is called sedimentation. Now gently pour the water in another container. This process is called decantation.

    2.   Filtration: Allow the mixture to pass through the filter paper. Water will pass through the filter paper and mud will get collected on the filter paper. This process is called filtration.

Q25. How will you separate the components of the following?

     a.   Green Chillies from pulao

Handpicking

     b.   Green gram from Chick pea

Handpicking

     c.   Pebbles from rice

Hand picking or sieving

     d.   Tea leaves from tea

Sieving or straining

     e.   Wheat bran from wheat flour

Sieving

     f.    Sand and husk

Winnowing

     g.   Wheat, sugar and stalks

Stalks being lighter can be separated by winnowing. Wheat and sugar can be separated by sieving.

     h.   Water and kerosene

Separating funnel

     i.     Rice and sugar

Sieving