Colloids

INTRODUCTION: Thomas Graham (1861) divided substances into two types, i.e. Crystalloids and colloids. He
observed that Crystalloids are the substances which pass through a semi permeable membrane. For example:
Sugar, urea, sodium chloride while colloids are those substances which do not pass through a semi permeable
membrane. For example: starch, glue. Graham thought that the difference in the behavior of ‘crystalloids’ and
‘colloids’ was due to the particle size so later on this concept was neglected and a new concept was given on
the basis of particle size.

On the basis of particle size, substances are divided into following three categories:

1. True solution: If the particle size ranges from 1Ao to 10Ao then the solution is called true solution.
OR It is a homogeneous mixture of solute and solvent, e.g. solution of sugar and water.
2. Colloids: If the particles size ranges from 10Ao to 2000Ao then the solution is called as colloidal solution.
OR Colloids are the solutions, which are intermediate between true solution and suspension. In other words,
the size of colloidal particle is in between of a true solution and suspension.
OR It may also be defined as: the heterogeneous mixture of dispersion phase and dispersion medium e.g. flour
in water.
3. Suspension: If the particle size is greater than 2000Ao then it is called as suspension.
OR It is a heterogeneous mixture made up of particles in a fluid e.g. dust in water.

COLLOIDAL SYSTEM (SOLUTION)

A colloidal system is that which is made of up two phases, i.e. Dispersion phase and Dispersion medium.
1. Dispersion phase: A phase in which particles are dispersed in a continuous phase or the substance distributed
as the colloidal particles is called the Dispersed phase.

2. Dispersion medium: The continuous medium, such as a gas, liquid, or solid, in which a disperse phase is
distributed is called dispersion medium or a phase in which the colloidal particles are dispersed is called the
Dispersion medium.

For Example: For a colloidal solution of copper in water, copper particles constitute the dispersed phase and
water the dispersion medium.

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TYPES OF COLLOIDAL SYSTEM (SOLUTION)
On the basis of phase of dispersion phase and dispersion medium, these are 8 types of colloidal solutions which
are listed below.

DIFFERENCE BETWEEN TRUE SOLUTION, COLLOIDAL SOLUTION AND SUSPENSION:

True solution Colloidal Solution Suspension

1 It is a Homogenous mixture It is a Heterogeneous mixture It is a Heterogeneous mixture

2 Particle size ranges from 1Ao to Particle size ranges from 10Ao to Particle size is greater than
10Ao 2000Ao 2000Ao
3 It is more stable It is stable but less than true It is unstable
solution
4 It can`t be filtered It can be filtered by ultra-filter It can be filtered by simple
paper filter paper
5 Particle can`t be seen Particle can be seen by ultra- Particle can be seen by naked
microscope eye
6 Brownian movement can`t be Brownian movement can be Brownian movement can be
observed observed observed
7 It does not show Tyndall effect Shows Tyndall effect Shows Tyndall effect

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FURTHER SUBDIVISON OF COLLOIDAL SYSTEM (SOLUTION)
When the dispersion phase is a solid and dispersion medium is a liquid then the solution is called Sols or Colloidal
solution. On the basis of interaction between dispersion phase and dispersion medium, sols/colloidal solutions
are further divided into two classes.
1. Lyophilic sols (solvent-loving)
2. Lyophobic sols (solvent-hating)
1. LYOPHILIC SOLS (COLLOIDS): If there is strong interaction between dispersion phase and dispersion medium
of sol, then such a sol is called lyophilic sol or it is also called as solvent loving colloid.
Example: Dispersions of starch, gum, and protein in water.
2. LYOPHOBIC SOLS (COLLOIDS): If there is no interaction between dispersion phase and dispersion medium of
sol, then such a sol is called lyophobic sol or it is also called as solvent hating colloid.
Example: Dispersion of gold, iron (III) hydroxide and sulphur in water.
CHARACRTERSTICS OF LYOPHILIC SOLS (COLLOIDS)
1. There is strong interaction between dispersion phase and dispersion medium.
2. It can be easily prepared by mixing of dispersion phase and dispersion medium.
3. It is highly solvated due to strong interaction.
4. Stability is high due to strong interaction.
5. It is reversible in nature.
6. Particles may have little or no charge at all.
7. Do not exhibit Tyndall effect.
8. Viscosity is high then that of pure solvent.
9. Precipitated by high concentration of electrolytes.
10. Particles migrate to anode or cathode or not at all.
CHARACTERSTICS OF LYOPHOBIC SOLS (COLLOIDS)
1. There is no interaction between dispersion phase and dispersion medium.
2. It can`t be easily prepared. Special method of preparation is required.
3. There is no solvation occurs.
4. Stability is very low due to weak interaction.
5. It is irreversible in nature.
6. Particles carry negative or positive charge.
7. It exhibits Tyndall effect.
8. Viscosity is same as that of pure solvent.
9. Precipitated by low concentration of electrolytes.
10. Particles migrate to either anode or cathode.

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COMPARISON OF LYOPHILIC AND LYOPHOBIC SOLS

LYOPHILIC SOLS LYOPHOBIC SOLS

1 Strong interaction between dispersion No interaction between dispersion phase and
phase and dispersion medium. dispersion medium.
2 Easily prepared by mixing of dispersion Special method of preparation is required.
phase and dispersion medium.
3 Little or no charge on particles. Particles carry positive or negative charge.

4 Reversible in nature. Irreversible in nature.

5 Particles generally solvated. No solvation of particles.
6 Viscosity higher than dispersion medium. Viscosity almost the same as of medium.

7 Stability is high due to strong interaction. Stability is very low due to weak interaction.
8 Precipitated by high concentration of Precipitated by low concentration of
electrolytes. electrolytes.
9 Particles migrate to anode or cathode or Particles migrate to either anode or cathode.
not at all.
10 Do not exhibit Tyndall effect. Exhibit Tyndall effect.

DEFINTIONS:
1. Tyndall effect: The phenomenon of the scattering of light by the sol particles is called Tyndall effect.
2. Brownian movement: The continuous rapid zig-zag movement executed by a colloidal particle in the
dispersion medium is called Brownian movement or motion.
3. Coagulation or Precipitation: The settling down of the discharged sol particles is called coagulation or
precipitation of the sol.
4. Ultra-filtration: The separation of the sol particles from the liquid medium by filtration through an ultrafilter
is called ultrafiltration.
5. Sols (Colloidal solution): When the dispersion phase is a solid and dispersion medium is a liquid then the
solution is called Sols or Colloidal solution.
6. Hydrosols or Aquasols: The colloidal solutions in water as the dispersion medium are termed Hydrosols or
Aquasols.
7. Alcosols: When the dispersion medium is alcohol then it is referred as alcosols.
8. Benzosols: When the dispersion medium is benzene then such sol is called benzosols.

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