INDEX
Chemistry Project Report
Project Report on Adsorption
Chemical Adsorption
Physical Adsorption
Introduction towards
Adsorption
Causes of Adsorption
Classification of Adsorption
Factors on which adsorption
depend
Types of Adsorption
Freundlich's adsorption
isotherm
Application of adsorption
Project Report Adsorption
The situation existing at the surface of
Liquid or a solid is different from them
in interior. For example, a molecule in
the interior of a liquid is completely
surrounded by other molecules on all
sides and hence the intermolecular
forces of attraction are exerted equally
in all directions. however, a molecule
at the surface of a liquid is surrounded
by large number of particles in the
liquid phase and fewer number of
particles in vapour phase i.e. in the
space above the liquid surface. As a
result these molecules lying at the
surface, experiences some net inward
forces of attraction which cause
surface tension. Similar inward forces
of attraction exist at the surface of a
solid.
Because of the unbalanced inward
forces of attraction of free valances at
the surface, liquid and solids have the
property to attract and retain the
molecules of a gas or dissolved
substance on the their surfaces with
which they come in contact.
Adsorption - Definition
Definition of Adsorption : The
phenomenon of attracting and
retaining the molecules of a substance
on the surface of a Liquid or a
solid resulting in the higher
concentration of the molecules on the
surface is called Adsorption.
The substance thus adsorbed on
surface is called Adsorbate and the
substance on which it is adsorbed is
called Adsorbent.
Causes of Adsorption
Adsorption arises at the surface of
solids as a result of presence of
unbalanced forces at the surface.
These forces develop either during the
crystallization of solids or by virtue of
the presence of unpaired e- in d-
orbital.
Characteristics of
Adsorption
1. It is specific and selective in nature.
2. It is accompanied by decrease in
the free energy of the system. When G
becomes zero, Adsorption equilibrium
is established.
3. Adsorption is spontaneous process
therefore change in free energy (G) for
the process is negative.
According to Gibb's Helmhotz equation
:
G = H - TS
G = -Ve ; H = -Ve
( it is exothermic process)
And S is -Ve because adhering of gas
molecules to the surface lowers the
randomness.
Factors on which adsorption depend
1. Surface area of Adsorbent :
Greater the surface Area of Adsorbent,
greater is the volume of gas adsorb
2. Nature of gas being Adsorb :
Higher the critical temperature of gas,
greater is the among of that gas
adsorbed.
3. Temperature :
Adsorption decreases with increase in
temperature and vice - versa.
4. Pressure :
Adsorption of a gas increase with
increase of pressure because on
applying pressure gas molecules
comes close to each other.
Types of Adsorption
1. Physical Adsorption :
When a gas is bled on the surface of a
solid by Vander wall's forces without
resulting in to formation of any
chemical bond between the Adsorbate
and Adsorbent. It is called physical
adsorption or vender wall's adsorption
or also known as physicosorption.
2. Chemical Adsorption :
When a gas is held on the surface of
solid by forces similar to those of a
chemical bond, the type of adsorption
is called chemical adsorption or
chemisorptions. It is also known as
Longmuir adsorption.
Freundlich's adsorption
isotherm
A graph between the amount adsorbed
by an adsorbent and the equilibrium
pressure of the adsorbate at a
constant temperature is called the
Adsorption isotherm.
At low value of p, the graph is nearly
straight and sloping this is represented
by follow equation :
or = constant x p1 ------------------
(a)
At higher pressure becomes
independent of the values of p. in this
range of pressure :
p0 or = constant x p0 ------------------
(b)
in the intermediate range of pressure,
will depend on p raised to the powers
between 1 and 0. i.e. fractions. For a
small range of pressure values, we
can write :
------------------- (c)
Adsorption Isobars :
A graph drawn between the amount
adsorbed () and temperature 't' at a
constant equilibrium pressure of
adsorbate gas is known as Adsorption
isobars.
(i) Physical Adsorption isobar (ii)
Chemical Adsorption isobar.
Application of Adsorption
1. In preserving vacuum : In Dewar
flasks activated charcoal is placed
between the walls of the flask so that
any gas which enter in to the annular
space either due to glass imperfection
or diffusion through glass is adsorbed.
2. In gas masks : All gas masks are
devices containing suitable adsorbent
so that the poiseness gases present in
the atmosphere are preferentially
absorbed and the air for breathing is
purified.
3. In clarification of sugar : Sugar is
decolorized by treating sugar solution
with charcoal powder. The later
adsorbs the undesirable colours
present.
4. In softening of hard water : The
use of ion exchangers for softening of
hard water is based upon the principle
of competing adsorption just as in
chromatography.
5. In removing moisture from air in
the storage of delicate instruments :
Such instruments which may be
harmed by contact with the moist air,
are kept out of contact with moisture
using silica gel.
6. In Adsorption indicator : Varous
dyes, which owe their use to
adsorption, have been introduced as
indicator particularly in precipitation
titration. For example, KBr is easily
titrated with AgNo3 using eosin as
indicator.
