Unit -2 separation of substances CLASS-6

Unit -2 separation of substances

Qus1-What is threshing? Explain the ways in which threshing is commonly done?

Ans the process of beating harvested crops to separate the grains from the stalks is called threshing. It is done manually (by hand) or with the help of machines

Qus-2What is winnowing? How is it done?

Ans-The mixture of chaff and grain is taken in a winnowing basket. The farmer stands at a higher level and lets the mixture fall to the ground. The grain, being heavier, falls almost vertically whereas the lighter chaff is carried away by the wind .the separated chaff is used as fodder for cattle.

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Qus3-What is hand picking? When is this method used?

Ans-Rice ,wheat, pulses, etc, that be buy from the market may contain impurities (unwanted or harmful particles ) in the form of small stones , un wanted grains ,etc, often  ,these impurities look very different from the food item and can be spotted easily. The method of separation used in such a case is hand picking.

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Qus4-Define saturated solution. How would you prepare a saturated solution of sugar in water?

Ans-a saturated solution is the solution in which no more of the solute can be dissolved?

If we keep adding spoonfuls of sugar to water and stir the solution each time we will notice some grains of sugar at the bottom of the solution. This shows that no more sugar can be dissolved. We say that the solution has become saturated.

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Qus5-How can the solubility of a substance be increased?

Ans-Solubility is the ability of a substance to get dissolved in a given liquid. The quantity of a substance that can dissolve in hot water is much more as compared to that in cold water there are some other factors that increase the solubility of a solute. We can observe this by taking two glasses of water and adding a whole sugar cube in one glass and powdered or crushed sugar cube in the other. Sugar in the powdered from dissolves first.

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Short answer questions,

Qus1 -name the different methods of separation?

Ans-sieving,thressing,winnowing,and hand picking

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Qus2-When can sieving be done?

Ans-the process of sieving is also used to separate pebbles and stones from and at construction sits.

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Qus3-Why is it not advisable to sieve wheat flour?

Ans-Sieving wheat flour is not advisable as wheat bran, which is removed during sieving, is very rich in nutrients and is also a rich source of fiber. It is better to remove visible impurities by hand picking.

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Qus4-Differentiate between sedimentation and decantation

Ans-The process of separating insoluble solids suspended in a liquid by allowing them to settle down is called sedimentation

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Qus5-What is filtration? Give two common examples of filtration?

The process by which two substances (an insoluble solid and a liquid) are separated by passing the mixture through filtering devices is called filtration.

Ex- After preparing tea, we filter out the tea leaves using a strainer. Filtration is also done to remove pulp from fresh fruit juice.

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Qus-6 How is a solute different from the solvent? Give two examples of common solute?

Ans- the substance that dissolves is called the solute and the substance in which the solute dissolves is called the solvent. The resulting mixture is called the solution.

Ex- sugar +  water =  sugar solution