Exercise :
1. Why do we need to separate different components of a mixture? Give two examples.
Ans : Separation of different components from a mixture is necessary o remove useful and no useful or harmful components.
For example: a) stones are separated from rice. b) Waters are evaporated from seawater forming solid salt.
2. What is winnowing? Where is it used?
Ans : Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air. This method is commonly used by farmers to separate lighter husk particles from heavier seeds of grain.
3. How will you separate husk or dust particles from a given sample of pulses before cooking?
Ans : The husk or dust particles are lighter, carried away by the wind. Therefore they can be separated by winnowing.
4. What is sieving? Where can it be used?
Ans : Sieving is a process which allows the fine particles to pass through the holes while the bigger impurities remain on the sieve. Sieving is used in the construction sites to remove pebbles and stones from the sand.
5. How will you separate sand and water from their mixture?
Ans : We will have to leave the mixture of sand and water for some time in a glass. After sometime, the sand will settle at the bottom. Then pour terminated water into the glass. Thus the mixture will be separated.
6. 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. Sieving allows wheat flour to pass through the holes while sugar remains on the sieve.
7. How would you obtain clear water from a sample of muddy water?
Ans : By the process of filtration we will obtain clear water from a sample of muddy water. Take a filter paper, fold it in the form of a cone and fix it onto a funnel. Then pour the mixture on the filter paper. Sold particles in terminated mixture will remain on the filter.
8. Fill in the blanks :
1. The method of separating seeds of paddy fro 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 the cream from mile is an example of filtration .
3. Salt is obtained from seawater 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 sedimentation and decantation.
9. True of False :
1. A mixture of milk and water can be separated by filtration – FALSE
2. A mixture of powdered salt and sugar can be separated by the process of winnowing – FALSE
3. Separation of sugar from tea can be done with filtration – FALSE
4. Grain and husk can be separated with the process of decantation – FALSE
10. 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 to the lemonade after dissolving sugar. It is possible to dissolve more sugar before adding ice, because the sugar does not dissolve when terminated temperature decreases.
Suggested Projects and Activities :
1) Visit a nearby dairy and report about the processes used to separate cream from milk.
Ans : The process by which cream is separated from milk is called centrifugation. The milk is poured in a big centrifuge machine. The milk is rotated at a very high speed in a container. In this process milk separates into cream and skimmed milk.
You have tried a number of methods to separate impurities like mud from water. Sometimes the water obtained after employing all these processes could still be a little muddy. Let us see if we can remove even this impurity completely.
2. Take this filtered water in a glass. Tie a thread to a small piece of alum. Suspend the piece of alum in the water and swirl. Did the water become clear? What happened to the mud? This process is called loading. Talk to some elders in your family to find out whether they have seen or used this process.
Ans : The alum is add to the muddy water and stir up the water. Wait for abut 30 to 40 mins and the sediments , mud will sink down to the bottom, leaving a clean water that you can filter with your water filter.