CHAPTER- 3 SEPARATION OF SUBSTANCES EXERCISE
Notes
1. Separation- The process of separating the components of a mixture of substances is called separation.
2. Methods of separation— 1. Handpicking, 2. Threshing, 3. Winnowing, 4. Sieving, 5. Sedimentation, decantation, and filtration, 6. Evaporation.
3. Handpicking— The method of handpicking can be used to separate some large particles of dirt, stones, and husk from wheat, rice, and pulses. The amount of such impurities is usually not very large.
4. Threshing— The process of separating grains or seeds from the stalks of dried plants is called threshing. In this process, the stalks are beaten to separate the grains.
- Sometimes the work of threshing is done with the help of bullocks.
5. Winnowing— The method of separating the components of a mixture in this manner is called winnowing.
- Winnowing is used to separate the heavier and lighter components of a mixture with the help of winds or air currents.
6. Sieving— The method of sieving is used to separate two components of a mixture that differ in their particle sizes.
7. Sedimentation, Decantation, and Filtration—
- The process in which the heavier components of a mixture settle down at the bottom when water is added is called sedimentation.
- The process of carefully pouring out the water along with the soil from a sedimented mixture without disturbing it is called decantation.
- The method of filtration (filtering) is used to strain tea leaves from tea. The filtration method is also used at home to make paneer (cottage cheese).
- To make paneer, lemon juice is added to the milk before boiling it. This produces a mixture of solid paneer particles and liquid. The paneer is separated from this mixture by filtering it through a cloth or a strainer.
8. Evaporation— The process of converting water into its vapour is called evaporation. Wherever water is present, the process of evaporation keeps occurring continuously.
9. Saturated Solution— A solution in which no more of a substance can dissolve is called a saturated solution of that substance.
EXERCISE
Question- 1. Why do we need to separate different components of a mixture? Give two examples.
Answer- Before using any substance, we need to separate the harmful and unwanted materials mixed in it. Example: Before cooking, we wash food items to remove impurities from them. For instance, rice is washed before cooking.
Question- 2. What is winnowing? Where is it used?
Answer- The method of winnowing is used to separate the heavier and lighter components of a mixture with the help of wind or air currents. This method is commonly used by farmers to separate light husk from heavier grains.
Question- 3. How will you separate husk or dirt particles from a given sample of pulses before cooking.
Answer- Before cooking, the handpicking method is used to separate husk and dust particles from a sample of pulses.
Question- 4. What is sieving? Where is it used?
Answer- Sieving is used to separate components of different sizes. In this method, the smaller-sized components pass through the holes of the sieve, while the larger impurities remain in the sieve. This method is used to separate small particles of grains from flour.
Question- 5. How will you separate sand and water from their mixture?
Answer- To separate a mixture of sand and water, we will do the following-
- Keep the mixture of both in a beaker and leave it undisturbed.
- After some time, the sand will settle at the bottom of the beaker.
- Slowly pour the water from one beaker into another beaker.
- We can also use filter paper to remove the fine particles of sand.
Question- 6. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
Answer- Yes, a mixture of flour and sugar can be separated by the method of sieving using a sieve.
Question- 7. How would you obtain clear water from a sample of muddy water?
Answer- To obtain clean water from muddy water, we will do the following:
- Pour the muddy water into a beaker and leave it undisturbed for some time.
- After some time, the impurities will settle at the bottom of the beaker.
- The upper layer is clean water; pour it into another beaker.
- To remove fine impurities, filter it again with the help of filter paper.
Question- 8. Fill up the blanks
(a) The method of separating seeds of paddy from its stalks is called ________.
(b) When milk, cooled after boiling, is poured onto a piece of cloth the cream (malai) is left behind on it. This process of separating cream from milk is an example of ________.
(c) Salt is obtained from seawater by the process of _______.
(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 _______.
Answer- (a) The method of separating seeds of paddy from its stalks is called Threshing.
(b) When milk, cooled after boiling, is poured onto a piece of cloth the cream (malai) is left behind on it. This process of separating cream from milk is an example of Filtration.
(c) Salt is obtained from seawater by the process of Evaporation.
(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 Decantation.
Question- 9. True or False?
(a) A mixture of milk and water can be separated by filtration.
(b) A mixture of powdered salt and sugar can be separated by the process of winnowing.
(c) Separation of sugar from tea can be done with filtration.
(d) Grain and husk can be separated with the process of decantation.
Answer- (a)- False, (b)- False, (c)- True, (d)- False.
Question- 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?
Answer- We should dissolve the sugar before adding ice.
Compared to cold water, sugar dissolves faster in hot water. Therefore, we can dissolve more sugar in the water before adding ice.