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Phase Rule in three component system
1. Samrat Prithviraj Chauhan
Government College,Ajmer
Seminar Project
Department of Chemistry
Submitted by – Deepak Gahlot
Class – M.Sc. Semester I
Topic : Application of phase rule to three component system –
acetic acid + chloroform + water.
2021-2022
2. • Basics.
• Phase rule.
• Three component system.
• Graphical representation of ternary system.
• Water-acetic acid-chloroform system.
• Conclusion.
• Reference.
3. Homogeneous solution : A homogeneous solution means a
solution which is of uniform (similar) composition. For
example – 1 spoon sugar mixed in 1 glass of water.
Heterogeneous solution : A heterogeneous solution is one
which is of distinct composition (looks different).For example
– sand and water solution.
Miscible liquid : Miscible liquids are those which will
completely dissolve/mix in each other. For example –
lemonade.
Partially miscible liquids : Partially miscible liquids are those
liquids which will not completely dissolve or mix but some
amount of them will. For example – 1-Butanol and water.
4. Immiscible liquids : Immiscible liquids are those which will not
mix at all and will remain in separate layers. For example - oil
and water.
Phase : homogeneous, physically distinct, mechanically
separable part of a system and is in dynamic equilibrium with
each other. For example – oil, water and sugar solution.
Component : It means the minimum number of constituents
sufficient for determining the composition of all phases of a
system. For example – ice,water and water vapour exists in 3
phases but their constituent element is same (H2O),hence 1
component system.
Degree of freedom : It is the minimum no. of independent
variables such as temperature,pressure and concentration
that must be ascertained so that a given system in equilibrium
is completely defined.For example: water and water vapour is
a 2 phase system having DOF 1 since at 100°C,pressure is 1 atm.
5. The phase rule was discovered by “Josiah Willard Gibbs”
in 1875 and is known as Gibbs phase rule.It states that in
a heterogeneous system in equilibrium,the sum of no. of
phases and number of degrees of freedom is equal to the
number of components plus two.Mathematically,it is
expressed as –
where P = number of phases
F = number of degree of freedom
C = number of components
2 = additional variable of temperature and pressure
P + F = C + 2
6. For three component system,phase rule equation becomes
If we consider minimum no. of phases (P=1),then to represent
three component system , 4 DOF i.e; 4 variables viz.
pressure,temperature,and composition of two components
will be required.
Graphical representation with 4 variables is
not possible,so 2 variables pressure and temperature are kept
constant.Hence reduced phase rule for 3 component system is
F = C - P + 2 = 3 - P + 2 = 5 - P
F = 3 - P
7. The popular method of representing a ternary system was given
by Stokes & Roozeboom and is called as triangular plot. In this
method , variation of compositions of three components at
constant pressure and temperature are expressed by means
of equilateral triangle.Each apex of the triangle is taken as 100
% (weight or mole)of the component with which it is designated.
Each side of the triangle is divided into 10 equal parts and then
lines parallel to three sides are drawn.Any point on any side of
the triangle referstocompositionof2 components in the system.
While any point in the triangle represents compositions of all the
3 components.
9. This 3 component liquid system is a type of one pair of partially
miscible liquids.Of the three components H2O,CHCl3 & CH3COOH
the acetic acid is completely miscible with water and chloroform
separately but water and chloroform are only partially miscible
between themselves.
H2O & CHCl3 being partially miscible forms
layers each saturated with other component.The mixture will
form two conjugate solutions given by the points b and c as
shown in the graph.
10. When CH3COOH is added to this solution,the miscibility of H2O
& CHCl3 is enhanced.’A’ will distribute itself between the two
layers and the layers become conjugate ternary solutions.The
composition of these two solutions are given by the points b’
and c’.The solution is still heterogeneous.
As more and more CH3COOH is added,
then the two layers emerge into a clear solution forming only
one layer containing all the three liquids.
The points come more closer till it merges to a
point K. The composition of two layers at this point is same and
this K point is called as the plait point or isothermal critical
point.
11. Any solution outside the curve XKY will be homogeneous
and inside it will be heterogeneous. This curve is known
as binodal curve.The points joined together form parallel
lines and are called as tie lines.
These tie lines are parallel
because the added constituent ( acetic acid ) distributes
itself equally in both the layers of water and chloroform.
Thus, they are horizontal tie lines in this case. The tie line
will not be parallel always but in slope form if the added
component dissolves more in one than the other.
12. Fig. – Three liquids with one partially miscible pair.
13. Ternary phase diagram construction is the best approach
to study all the types of formulations by mixing of water,
oil and and surfactant.It provides the scientific basis for
the screening of different formulation components and
determination of optimum conditions for existence of
equilibrium.
It is widely used in research and formulation studies of
various pharmaceutical formulations and process.
Spectrometric study of Au,Ag and Cu to find the impurity
we use this 3 component phase rule application.
14. Advanced physical chemistry by D.N.Bajpai (S.Chand),
page no. 393…
Advanced physical chemistry by Gurtu & Gurtu (Pragati
Prakashan),page no. 240…
Advanced Physical Chemistry by Puri Sharma Pathania,
page number 692…
