Chapter 5 Separation of Substances Solutions
Question - 1 : - Why do we need to separate different components of a mixture? Give two examples.
Answer - 1 : -
We carry out the separation of substances for the following purposes:
(a) To remove the un useful or harmful component : For example, removing tea leaves after making tea.
(b) To obtain the useful component : For example, getting wheat, rice grains after separating husk, dirt, etc.
(c) To remove impurities for getting a pure sample : For example, obtaining sugar crystals from jaggery (gur) or salt from sea water.
Question - 2 : - What is winnowing? Where is it used?
Answer - 2 : -
Winnowing is the process of separating wheat or rice grains from the husk. Wheat grains and husk are different in weight, husk is lighter than wheat. When the mixture is allowed to fall down from a height, the wind carries the lighter husk with it and the heavy wheat grains fall vertically down on the ground.
Question - 3 : - How will you separate husk or dirt particles from a given sample of pulses before cooking?
Answer - 3 : -
Husk or dirt particles from pulses can be separated by handpicking method.
Question - 4 : - What is sieving? Where is it used?
Answer - 4 : -
Sieving is the method to separate particles of different sizes. Undesirable particles can be separated from grains by this method. The size of holes in the sieves depends upon the size of the particles. In cashewnuts factories, the cashewnuts of different sizes are separated by sieving. Jewellers also separate pearls of different sizes by this method.
Question - 5 : - How will you separate sand and water from their mixture?
Answer - 5 : -
Take a beaker (100 ml) half filled with given sample of water. Stir the water thoroughly. Now keep the beaker undisturbed for some time. Sand gets settled down at the bottom of the beaker. After some time, water can be separated by decantation process and sand is left in the beaker.
Question - 6 : - Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
Answer - 6 : -
Yes, we can separate sugar from wheat flour by sieving. In the mixture of sugar and wheat flour, sieving allows the fine flour particles to pass through the holes of the sieve, while the sugar particles remain on the sieve.
Question - 7 : - How would you obtain clear water from a sample of muddy water?
Answer - 7 : -
We can purify the muddy water by loading. First, we take a beaker (100 ml) half filled with muddy water. Now take a piece of alum (phitkari) and a thread (about 30 cm in length). Tie firmly the one end of the thread with alum and hold the other end of the thread with hand.
Now dip the alum in the water and move it slowly in a circular path for about one minute. Remove the alum and keep the beaker undisturbed for some time. During this process, we will find that the dust particles get loaded and become heavier and settle down at the bottom of the beaker quite rapidly. When all the dust particles settle down, the water becomes clear. The clear water is then decanted into another beaker.
Fill in 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 - 8 : -
(a) threshing
(b) filtration
(c) evaporation
(d) decantation
Question - 9 : - True or false:
(a) A mixture of milk arid 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 - 9 : -
(a) False
(b) False
(c) False
(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 - 10 : -
We should add ice to lemonade after dissolving sugar. Without ice, sugar dissolves easily in lemon juice, because solubility depends on the temperature. If sugar is added to ice-cold solution of sugar and lemon juice, the solubility of sugar will decrease.