6th Standard, Science, Chapter 3
Separation of Substances
Exercises
1. Why do we need to separate different components of a mixture? Give two examples.
Answer: We see that, before we use a substance, we need to separate harmful or non-useful substances that may be mixed with it. Sometimes, we separate even useful components if we need to use them separately.
Example 1: Tea leaves are separated from the liquid with a strainer, while preparing tea. Example 2: Milk or curd is churned to separate the butter
2. What is winnowing? Where is it used?
Answer: Separating method of heavier and lighter components of a mixture by wind or by blowing air is called winnowing. Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.
3. How will you separate husk or dirt particles from a given sample of pulses before cooking?
Answer: The husk particles are carried away by the wind. The seeds of grain get separated and form a heap near the platform for winnowing. The separated husk is used for many purposes such as fodder for cattles.
4. What is sieving? Where is it used?
Answer: We need to remove impurities and bran that may be present in the flour. We use a sieve and pour the flour into it. This method is called sieving. It is used before us cooking.
5. How will you separate sand and water from their mixture?
Answer: Sand and water can be separated from their mixture through sedimentation and decantation. When the heavier component like sand settles bottom after water is added to it, the process is called sedimentation. When the water is removed, sand will remain and the process is called decantation. If any fine sand particles are still floating or were accidentally poured over, we can achieve complete separation using a paper filter by filtration.
6. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
Answer: Yes. It is possible to separate sugar mixed with wheat flour. We can separate sugar mixed with wheat flour by sieving method. The smaller, finer wheat flour particles will pass through the holes. The larger sugar crystals will be retained in the sieve.
7. How would you obtain clear water from a sample of muddy water?
Answer: We can obtain clear water from a sample of muddy water by sedimentation,
Decantation and Filtration method. Heavier mud particles will settle at the bottom. Carefully pour the clearer water at the top into another container without disturbing the mud at the bottom. Pour this decanted water through a filter paper or a clean cotton cloth to remove any remaining mud.
8. Fill up the blanks
(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 sedimentation and decantation.
9. True or false?
(a) A mixture of milk and water can be separated by filtration. – False
(b) A mixture of powdered salt and sugar can be separated by the process of winnowing. – False
(c) Separation of sugar from tea can be done with filtration. – False
(d) 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?
Answer: We should add ice to the lemonade after dissolving sugar. In this case it would be possible to dissolve more sugar. It is possible to dissolve more sugar before adding the ice, because higher water temperature increases sugar solubility.
SUGGESTED PROJECTS AND ACTIVITIES
1. Visit a nearby dairy and report about the processes used to separate cream from milk.
2. 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. 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.
