Separation of Substances, Why?
We need to separate substances in many cases. Let there be any impure thing added to a thing that is useful, ,we will have to separate them, or if two useful things are mixed together and we need both of them separately, then also we need to separate substances. Also if there is a situation in which a useful substance is found but some impurity is always attached to it , then we need to separate substances. The separation of substances is done in many ways. These ways we are going to study in this chapter. No let us do some questions related to the chapter.
1. Why do we need to separate substance? Give any two reasons.
Answer- a) To separate two different but useful components.
b) To remove impurities , non useful or harmful impurities / components from the mixture.
2. Write down any five situations where we separate substances.
Answer- a) Separate tea leaves from tea.
b) Separate stones from rice or pulses.
c) Separate pieces of stones, stalk and husk from wheat grains.
d) removing cotton seeds from cotton bolls.
e) Sieving finer sand from bigger sand particles and stones and separating them.
3. How do your mother separate stones from pulses before preparation?
Answer- By Hand Picking.
4. How is sand separated from stones and marbles?
Answer- By Sieving.
Additional Questions
1. Can we separate salt from water?
Answer-Yes, we can separate salt from water.
2. Is washing clothes also a kind of separation?
Answer-Yes
3. How do we separate tea leaves from tea?
Answer- We can separate tea leaves from tea leaves using strainer (sieve).
4. How can we separate chilies from prepared curry?
Answer- We can separate chilies from prepared curry by hand picking.
Methods of separation
HANDPICKING and THRESHING
1. What is Hand picking. Give an example where this method is used.
Answer-Handpicking is the easiest method of separation of substances in which we use separate substances by using our hands. This method is used for separating slightly large impurities like the piece of stones , dirt from wheat rice or pulses.
2. What is Threshing? Give an example of Threshing?
Answer- Threshing is the process in which the stalks of a crop are beaten to free the grain seeds. This method is used to separate the stalks of grain crops from seeds so that seeds may be used. Threshing is done with the help of Bullocks or machines.
WINNOWING, SIEVING, DECANTATION SEDIMENTATION & FILTRATION
1. What is Winnowing? Explain
Answer- Winnowing is a process of separation in which heavier and lighter components of a mixture are separated with the help of wind or by blowing air.
2. What is Sieving? How is it done?
Answer- Sieving is process of separation in which sieve is used to remove larger impurities from finer important useful things. For Example; A sieve is used in kitchen to get finer wheat flour and remove impurities, also Sieving is used in construction sites to get finer sand from a mixture of sand, stone and dirt particles.
3. What is Sedimentation,Decantation and Filtration?
Answer- Sedimentation, Decantation and Filtration are the process which are used to separate a mixture of heavier components in water , for example dust/ sand mixed in water or a mixture of insoluble liquids.
In Sedimentation the mixture is allowed to stand for some time such that heavier component of liquid settles down.
In decantation after sedimentation the lighter liquid / component of mixture is removed slowly such that heavier component remains in the bottom.
In Filtration, the liquid which has been decanted is passed through a filter so that finer components of the mixture which weren’t removed by above two process may be removed out.
EVAPORATION and CONDENSATION
1.How is evaporation used to separate salt dissolved in water from water?
Answer- By boiling we will evaporate water and the substance left in water will be salt only. In this way evaporation can be used for separation.
2.What is condensation? How can we get pure water from condensation?
Answer- Condensation is the process of conversion of vapour into liquid. By boiling we can get vapour and this vapour can be converted into pure water by putting a cold lid over the boiling vessel.
3. Can water dissolve any amount of substance in it? What is a saturated solution?
Answer- No water cannot dissolve any amount of substance in it. If we keep on adding a soluble substance in water , there comes a stage when no more substance gets dissolved in the solution, at this stage the solution is said to be saturated.