Introduction-
We see and use a number of substances in our
daily life. These are pure as well as impure mixture. Most of them are mixture.
E.g.- Air, Water, Milk, etc.The separation of harmful or useless component is
done from useful ones by different methods.
Pure
Substance-
Those substances which are made up of only one
kind of particles are called as pure substances. e.g.- All elements like Hydrogen, Gold, Carbon etc. and
Compounds like Water, Sodium Chloride etc.
Mixture-
Those impure substances in which two or more
other substances are found are called mixture.
The ratio of components in the mixture is not
fixed. Their individual chemical characteristic is retained. Components of a
mixture can be separated. A mixture can be solid, liquid or gas. The mixtures
can be –homogeneous or heterogeneous. The components of homogeneous mixture
cannot be seen separately. e. g.- Steel, Petroleum, milk, Air etc. The
components of heterogeneous mixture can be seen separately. e. g.- Rice and
stone, sand and iron etc. etc.
Separation
of substances-
The separation of substances is done to remove
harmful component or unwanted component or to obtain pure or useful component
from a mixture. The common methods are-
1.
Hand Picking-
The process of separating of large unwanted components of the mixture by hand is
called handpicking. e. g.- Small pieces of stones from rice, pulses etc.
2.
Threshing-
The process of separating of grains from their straw and chaff is called
threshing. It is done manually by hand or by thresher machines.
3.
Winnowing-
The process of separating of lighter components from heavier component by using
wind is called winnowing. e. g. Husk (lighter) from the grains (heavier).
4.
Sieving-
The process of separating different size components of a mixture by using sieve
is called sieving. e. g. Tea from tea
leaves by sieve, Fine sand from gravels and pebbles of stone by using
wire-mesh.
5.
Magnetic separation-
The process of separating of a non-magnetic component from a magnetic component
of the given mixture is called magnetic separation.
e.g.- Separation of iron objects from scrap
yard, Iron nails, from sand etc.
6.
Sedimentation, Decantation and Filtration- The process of separating of insoluble solids
from liquid in its solution is done by sedimentation, decantation and
filtration. These are interrelated processes.
The heavier insoluble particles are allowed to settle down at the bottom of container. It is called sediment.
The pouring of liquid part without disturbing
the sediment is called decantation.
The process by which very fine insoluble
components are removed using filter/ filter paper is called filtration.
7.
Evaporation and Condensation- The changing of water into water vapour is
called evaporation or vaporization. Evaporation is used to separate water
soluble solids from liquids.
Evaporation is used to make salt from salty
water. The liquid evaporates and heavy solid component is left behind.
Condensation is changing of water vapour into
liquid form by cooling. The solid impurities are left behind on evaporation.
Then pure liquid is obtained from this vapour by condensation.
8.
Centrifugation or Churning-
The fine insoluble solid is separated from liquid-solid mixture by rotating at
very high speed is called centrifugation. e. g.- Butter from milk, drying of
wet clothes by squeezing water in washing machine, blood cells from plasma etc.
Saturated
Solution-
The solute and solvent together is called as
solution. e. g.- Sugar is a solute and water is a solvent that together forms a
solution.
Solute (Sugar) + Solvent (Water) = Solution
If more solute is added in the solution it
will become denser. A solution in which no more solute can be dissolved is
called saturated solution. The solute will be seen more at the base of
container.
On increasing temperature of saturated
solution, more solutes can be added. On the other hand on decreasing the
temperature of saturated solution more solutes cannot be added.
Exercise
Questions
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