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Chemistry Project Report on “Adsorption”
I, ____________ student of ___________________ is doing
project report entitled “Adsorption” being submitted to
___________________is an original piece of work done by me.
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 :
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.
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 :
= constant x p1 ------------------ (a)
At higher pressure becomes independent of the values of
p. in this range of pressure :
= constant x p0
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 :
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
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
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.
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