There are three major groups of
mixtures,they are :-
a) Solution :-
·
A
solution is a homogeneous mixture of two or more components.
·
The
dissolving agent is called as solvent where as the substance which is dissolved
is called as solute.
·
The
components of a solution are unevenly distributed and cannot be seperated.
·
The
components of a solution are smaller in size up to 10-9 m .
Eg. Sugar and water
b) Suspension :-
·
A
suspension is a heterogeneous mixture containing solid particles that are
sufficiently larger than the particles found in the solutions and have a
average size up to 10-7 m .
·
The
Components of a suspension can be evenly distributed by mechanical means, like
shaking,stirring etc., but inspite of this the components settle down and
seperate from one another.
Eg. Oil and Water.
c) Colloids :-
·
The
Colloids were first discovered in 1860.
·
The
credit for the discovery of Colloids can be given to a Scottish Scientist,
Thomas Graham.
·
A
COLLOID is a substance which is microscopically dispersed (widely spread)
evenly throughout another substance.
·
Colloids
when mixed remain evenly distributed without settling forming a mixture known
as Colloidal Dispersion.
·
Colloids
are not visible with our naked eyes, but they can be seen under microscope.
·
The
Particles of colloids are intermediate in size between those found in solutions
and suspensions.
·
Colloidal
particles have an average size of 10-9 to 10-7 m .
·
The
Colloidal particles form Dispersed phase and the medium used for this is called
as Dispersion medium.
·
Dispersing
medium is the external phase and is found in the greater extent in the colloid
whereas the Dispersed phase is the internal phase and is found in the lesser
extent.
·
A
colloidal system can exist in any of the three forms solid, liquid or gaseous.
Eg :- Milk
Properties of Colloids
1) Tyndall Effect :-
A British Physicist John Tyndall in 1869
first observed this phenomenon and hence it is known as Tyndall Effect.
He observed that when a beam of light is
passed through a colloidal solution, the light is scattered by the particles
present in the colloidal solution.
This effect is often used as a measure
of the existence of a colloid.
2) Brownian Movement :-
The Molecules of the Dispersion medium
constantly collide with the colloidal particles thereby passing Kinetic Energy
to them.
This phenomenon results into zigzag
movement of the colloidal particles.
This zigzag movement of the colloidal
particles is known as Brownian movement.
3) Electrophoresis :-
The movement of the colloidal particles
under the influence of an applied electric potential is called as
Electrophoresis.
4) Electro-Osmosis :-
When the movement of the Colloidal
particles is prevented by some suitable means, it is observed that the
Dispersion medium itself begins to move under the influence of an electric
field. This phenomenon is known as Electro osmosis.
Types of Colloids
1) Sol :-In Sol the Dispersing medium is the Liquid whereas the Dispersed phase is the solid.
Eg :- Paint,Ink,Detergent etc.
2) Gel :- In Gels the Dispersing medium is the Solid whereas the Dispersed phase is the Liquid.
Eg :- Butter,Jelly etc.
3) Emulsion :- In the Emulsions both the Dispersing medium and the Dispersed phase are the liquids.
Eg :- Cometic lotions,Lubricants etc.
4) Foams :- In Foams the Dispersing medium is the Liquid whereas the Dispersed phase is the Gas.
Eg :- Shaving lather,whipped cream etc.
5) Aerosols :-In Aerosols the Dispersing medium is the Gas whereas the Dispersed phase is the Liquid.
Eg :- Insecticide sprays,Smog,Cloud,Fog
etc.
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