Separation of substances

1. No 1- Why do we need to separate different components of a mixture? Give two examples. 

Ans. When two or more substances are mixed together we call it a mixture. Sometimes different components of a mixture are not useful or may even harmful for us 

So we need to separate different components of a mixture. For example 

1.To remove impurities for getting a pure sample Salt from SEA water. 

2.To obtain the useful components for getting wheat or rice grains after separating. 

1. No 2- What is winnowing? Where it is used?

Ans. The process of separating heavier and lighter components of a mixture by wind or by blowing air is called winnowing. This method is commonly used by farmers to separate lighter husk particles from heavier grains.

Q.No3- How will you separate husk or dirt particles from a given sample of pulses before cooking?

Ans. The husk or dirt particles from a given sample of pulses before cooking can be separated by hand picking. 

Q.No 4- What is sieving? Where is it used?

Ans .  Sieving is a method used to separate the components of a mixture which are of different size. Sieving allows the fine flour particles to pass through the holes of the sieve while the bigger impurities remain on the sieve. In a flour mill, impurities like husk and stones are remain from wheat by sieving.

Q.No 5- How will you separate sand and water from their mixture?

Ans. A mixture of sand and water can be separated by sedimentation method or decantation method. 

Take the mixture of sand and water in a beaker .Allow the mixture to stand for sometime undisturbed. You will observe that sand particles start settling down at the bottom of the beaker forming sediment. The process of settling down of heavier, insoluble particles from a mixture is called sedimentation. The clear liquid above the sediment is gently poured off into another beaker, without disturbing the sediment. This process of transferring the clear water without disturbing sediments is known as decantation. 

Q.No 6- Is it possible to separate sugar mixed with flour?

If yes, how will you do it?

Ans. Yes, it is possible to separate sugar mixed with wheat flour by sieving. Sieving allows the fine wheat flour particles to pass through the holes of the sieve while the sugar remain on the sieve. 

Q.No 7- How would you obtain clear water from a sample of muddy water?

Ans. We can separate clear water from a sample of muddy water by loading process. 

Take a beaker half filled with muddy water and take a piece of alum. The loading of suspended particles is carried out by alum. The dissolved particles of alum in water loads on the fine dust particles. The particles become heavy and settle down to the bottom. The clear water is decanted .The suspended particles remains at bottom as sediment. 

Q.No 8- Fill in the blanks:

1. a) The method of separating seeds of paddy from its stalks is called _____

Ans. Threshing 

1. b) When milk, cooled after boiling, is poured onto a piece of cloth the cream is left behind on it. This process of separating cream from milk is an example of ______

Ans. Filtration 

1. c) Salt is obtained from seawater by the process of ______

Ans. Evaporation 

1. d) 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 ______

Ans. Decantation 

Q.No 9. True / False

1. A mixture of milk and water can be separated by filtration. 

Ans.-False 

2. A mixture of powdered salt and sugar can be separated by the process of winnowing. 

Ans. -False 

3. Separation of sugar from tea can be done with filtration. 

Ans.-False 

4. Grain and husk can be separated with the process of decantation. 

Ans.- False 

Q.No 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 in lemonade after dissolving sugar in it, because sugar dissolves more quickly before adding ice. It would be possible to dissolve more sugar before adding ice in the lemonade, because it dissolve more into hot than in cold.