B.Sc.

Part I (Chemistry Honours)

Paper I A: (Physical Chemistry)
Group-A: The States
Chapter 4. Colloidal State
 Definitions
 Example of colloids
 Classification
Definitions
A colloid is one of the three primary types of mixtures, with the other two being a
solution and suspension. A colloid is a solution that has particles ranging between 1 and
1000 nanometers in diameter, yet are still able to remain evenly distributed throughout
the solution. These are also known as colloidal dispersions because the substances
remain dispersed and do not settle to the bottom of the container. In colloids, one
substance is evenly dispersed in another. The substance being dispersed is referred to
as being in the dispersed phase, while the substance in which it is dispersed is in the
continuous phase.
When a dispersed phase is dispersed in a dispersion medium then depending on the
degree of dispersion, the systems are classed as i) true solution, ii) colloidal solution,
and iii) suspension.

Properties True solution Colloidal solution Suspension

Particle size 1 Å – 10 Å 10 Å – 1000 Å More than 1000 Å

Appearance Clear Generally clear Opaque

Nature Homogeneous Heterogeneous Heterogeneous

Separation by Not possible Not possible Possible

filtration
Separation by Not possible Possible Possible
cellophane paper
Visibility Not visible under Visible under Visible to naked
microscope ultra-microscope eye
Brownian motion Not observable Occurs May occur

DR.KUMARI SEEMA, (HOD), DEPARTMENT OF CHEMISTRY,

1
J.D.WOMEN,S COLLEGE,PATNA
Example of colloids

Colloidal AgCl, AgI, Ag proteinate (effective germicide), colloidal sulphur. Many

natural and synthetic polymers are important in pharmaceutical practice.
Polymers: These are macromolecules formed by polymerization or condensation of
small non-colloidal molecules e.g. proteins, natural colloids, plasma proteins which are
responsible for binding certain drug molecules so that the pharmacological action of the
drug molecule is affected by them. Starch and hydroxymethylallulose, cyclodeztrin are
also examples.

Types of Colloidal System

Classification based on the state of Aggregation:
Two phases are involved in a colloidal system
(1) Dispersed phase - solid, liquid, gas
(2) Continuous phase or dispersion medium --- solid, liquid, gas
General types of colloidal system:
Aerosol : solid or liquid disperses in gas

Emulsion : liquid in liquid

Foam : gas disperses in liquid (or solid)

Association colloid : aggregates of molecules of hundreds to thousands units, often

found in biological systems (cell membrane, micelle, vesicles).

Lyophilic colloid : the solute molecules are much larger than those of solvent.

Network colloid : consists of two inter-penetrating networks, and hard to specify which
is dispersed and which is continuous phase. (porous glass, opal glass, gels).

DR.KUMARI SEEMA, (HOD), DEPARTMENT OF CHEMISTRY,

2
J.D.WOMEN,S COLLEGE,PATNA
 Dispersion Medium / Dispersed Phase Type of Colloid System /Example
Continuous Phase

Solid Solid Solid sol/ Ruby, glass, Opal

Dispersion
Solid (Fat) Liquid (Water) Solid emulsion Pearl, cheese,
/gel Butter
Solid Gas Solid foam Lava, pumice,
Styrofoam
Liquid Solid Sol / Dispersion Paints, cell fluids

Liquid (Water) Liquid (Fat) Emulsion Milk, oil in water

Liquid Gas Foam Soap suds, Shave

cream, whipped
cream
Gas Solid Solid Aerosol Smoke

Gas Liquid Liquid Aerosol Fog, mist

Liquid Macromolecules Gel jello

Liquid Micelles of Micellar solution Liquid Soaps and

detergent Detergents
molecules

Classification Based on the affinity of the two phases:

Lyophilic colloids (solvent loving): They are so called because of affinity of particles
for the dispersion medium. Solutions of lyophiles are prepared by simply dissolving the
material in the solvent. Because of attraction between the dispersed phase and
dispersion medium, salvation (hydration in case of water) of the particles occur. Most
of these colloids are organic n nature e.g. gelatin, acacia, insulin, albumin. The solution
is viscous because of strong affinity for water (called gels).

Lyophobic colloid (solvent hating): The dispersed phase has little attraction to the
solvent (solvent hating). Their properties differ from the lyophilic (hydrophilic). They
are usually inorganic n nature e.g. gold, silver, sulphur. In contrast to lyophilic colloid,
it is necessary to use special method to prepare hydrophobic colloid.

DR.KUMARI SEEMA, (HOD), DEPARTMENT OF CHEMISTRY,

3
J.D.WOMEN,S COLLEGE,PATNA
Hydrophilic sol: For lyophilic sol when the dispersion medium is water then it is called
then they are called hydrophilic sols. Such as starch, glue, proteins, gelatin and certain
other organic compounds.

Hydrophobic sols: For lyophobic sol when the dispersion medium is water then it is
called then they are called hydrophobic sols. Examples are sol of metals, metal
sulphides, metal hydroxides, sulfur, phosphorous and other inorganic substances.

Properties Lyophobic sols or Lyophilic sols or

Hydrophobic sol hydrophilic sol
Detection of particles The particles may be The particles are not
readily detected by means detected by means of an
of an ultra-microscope ultra-microscope
Viscosity Hardly differs from that of Much higher than that of
the dispersion medium the dispersion medium
Electric charge All particles in a sol have The charge on colloidal
the same charge resulting particles depends upon the
from the adsorption of ions pH of the medium, since
from solution the particles readily adsorb
H+ or OH- ions. This
charge is often due to the
dissociation of the
molecules of the disperse
substance.
Migration of particles in The particles migrates in The particles may migrate
the electric field one characteristic direction in either direction or may
depending on the charge not migrate at all,
they bear depending on the pH of the
medium
Stability Dispersed particles are Dispersed particles are not
precipitated by the precipitated by small
addition of small amount amounts of electrolytes
of an electrolyte although large quantities
cause precipitation
Nature When the liquid is When the liquid is
removed, the resulting removed, resulting jelly-
solid does not form sol like solid is recoverted into
again by the simple sol by the addition of the
addition of the liquid liquid
Occurrence Generally, do not occur Most of these occur
naturally naturally

DR.KUMARI SEEMA, (HOD), DEPARTMENT OF CHEMISTRY,

4
J.D.WOMEN,S COLLEGE,PATNA