Experiment 1 : Phase Diagrams (Part A) ;
Determination of Phase Diagram for Ethanol/ Toluene/ Water System Theory
DATE
29 March
2014
TITLE
Determination of Phase Diagram for Ethanol/ Toluene/ Water System Theory Three-Component Systems
OBJECTIVES
·
To determine of the solubility limits of water and
two other liquids (ethanol and toluene), one of which is completely miscible
(ethanol) and the other is partly miscible with water (toluene) in a ternary
system.
·
To construct
the solubility curve of the system being studied on triangular diagram.
INTRODUCTION
First of all, the triangular diagram is used in the pharmaceutical formulation solutions.The main purpose in using the triangular diagram is to know the exact ratio of each component to be mixed with regarding of some other conditions such as temperature and pressure. The component mixed together and must be in the homogenous form In this experiment, there are three components which were Ethanol, Toluene and Water .Using the three component system,we can know the proper proportion that can be used to achieve homogeneous solutions. Water is insoluble and toluene, but as it were mixed together with ethanol, all three components can achieve homogenous solutions if proper proportion used in the three components system.But, there are some rules that had to be follow to use the three components system.
Each corner of the triangular
diagram represent a pure component which is 100% A. 100 % B and
100
% C.
Meanwhile, each side represent two-component system mixtures and within
triangular diagram itself present ternary components. Any parallel to a side of
a triangular shows constant percentage value for a component. The addition of a
third component to a pair of miscible liquids can change their mutual
solubility. If this third component is more soluble in one of the two different
components the mutual solubility of the liquid pair is decreased. However, if
it is soluble in both of the liquids, the mutual solubility is increased. Thus,
when ethanol is added to a mixture of benzene and water, the mutual solubility
of the liquid pair increased until it reached a point whereby the mixture
becomes homogenous. This approach is used in the formulation of solutions.
Examples of three-component systems that has been studied include castor oil/
alcohol/ water; peppermint oil/ propylene glycol/ water; peppermint oil/
polyethylene glycol/ water.
Following
the basis of describing the effect of intensive variable to various phase in a
system at equilibrium, which is the phase rule, it is determine that this
system have 4 degress of freedom. The four degrees of freedom are -
temperature, pressure, and any two from the three component
concentration.
F = C – P + 2
F = 3 – 1 + 2
F = 4
CHEMICAL
Ethanol, toluene and distilled water
APPARATUS
Conical flask, conical flask stopper, retort
stand and clamp, pipette, and burette.
PROCEDURE
1.
Mixtures of ethanol and toluene
in sealed containers measuring 100cm3 was
prepared containing the following percentages of ethanol (in percent):
10,25,35,50,65,75,90 and 95.
2.
20mL of each mixture was prepared
by filling a certain volume using a burette (accurately).
3.
Each mixture was titrated with
water until cloudiness is observed due to the existence of a second phase.
4.
A little water was added and
shake well after each addition.
5.
The room temperature was
measured.
6.
The percentage based on the
volume of each component was calculated when the second phase starts to
appear/separate.
7.
The points onto a triangular
paper was plotted to give a triple phase diagram at the recorded temperature.
8.
A few more measurements had been
done if necessary. The determination in the experiment had been done twice.
RESULT
PRACTICE
1)
Does the mixture containing 70% ethanol, 20%
water and 10% toluene appear clear or does it form two layers?
The mixture remain clear and form one
homogenous liquid phase.
2)
What will happen if you dilute 1 part of the mixture
with 4 parts of of
(a)
Water
(b)
Toluene
(c)
Ethanol
1 part mixture x 70% ethanol= 1 x 70/100= 0.7
part of ethanol
1 part mixture x 20% water= 1x 20/100= 0.2 part
of water
1 part mixture x 10% toluene = 1x 10/100= 0.1
part of toluene
So, in the mixture, there are 0.7 part of
ethanol, 0.2 part of water and 0.1 part of toluene.
(a) Water:
1 part of mixture + 4 parts of water
Hence,
based on the phase diagram, this mixture is under the area of the binomial curve, so 2 phase is formed.
(b) Toluene: 1 part of mixture + 4 parts of toluene
Hence,
based on the phase diagram, this mixture is outside the area of the binomial curve, so 1 phase is formed.
(c) Ethanol : 1 part of mixture + 4 parts of ethanol
Hence,
based on the phase diagram, this mixture is outside the area of the binomial curve, so 1 phase is formed.
DISCUSSION
A phase diagram shows the phases existing in equilibrium
at any given condition. According to the Phase Rule, a maximum of four
intensive variables (intensive properties) must be specified to completely
define the state of a three-component system. The intensive variables that are
usually chosen are pressure, temperature and concentration. According to the phase rule, a single phase
in a three-component system may possess four degrees of freedom.
F = C – P + 2 = 3 – 1 + 2 = 4
F = degree of freedom; C = component; P = phase
Since there are four degrees
of freedom, a complete graphical representation of the conditions of
equilibrium would require the use of four dimensions. A simplification is achieved by choosing one
of the intensive variables as a parameter. If pressure is chosen as a parameter
the condition of equilibrium can be represented by a triangular prisms, each
corresponding to a different pressure; the corners of the triangular bases
represent the pure components. However, such figures are difficult to construct
and cumbersome to use, hence the general practice is to use two of the
intensive variables as parameters thereby permitting a two-dimensional
representation of the conditions of equilibrium.
Liquid systems of three components consist of three
liquid components, two liquids and one solid or one liquid and two solids. In
this experiment, we investigate the behaviour of a system of three liquids:
ethanol, toluene and water, ethanol is miscible with both toluene and water but
toluene and water are quite insoluble in each other.
Regions where one or two phases appear have been
indicated in phase diagram for three-component system. When the three
components are mixed to give an overall system composition that falls in the
two phase region, the system will separate into two phases: a phase rich in
water and another rich in toluene. The curve of the plotted graph is termed as
binomial curve. The region bounded by the curve shows the presence of two
phases. The mixture within this region is cloudy in appearance due to phase
separation as the amount of ethanol is not sufficient for a homogenous mixture
to be produced. The region above the curve boundary shows one phase of
homogenous solution. Addition of ethanol which acts as surfactant allows the two
phase solution to be in one phase.
Based on the results obtained, when there is a higher
percentage of ethanol compared to the percentage of toluene in the mixture, the
volume of water needed to titrate the mixture until cloudiness is observed is
higher. This proves that the ethanol has increased the miscibility of the other
two components and more water is needed to break the homogeneity. A second
phase will only be separated out when the proportion of water added exceed the
theoretical percentage where three components are partially miscible.
There are some errors made during this experiment. One of
the errors is due to difference of tendency of cloudiness of the mixture.
Different person did the observation each time will cause the different degree
of cloudiness of mixture achieved. Hence, the volume of water added was not
accurate enough and will affect the results obtained.
Another error is parallax error. The eyes level of the
observer was not perpendicular to the reading scales. This causes inaccurate
measurement of liquid.
Ethanol and toluene are volatile liquids. Their volume
may be less than the actual needed value as some of them have been evaporated.
This affected the volume of water added for titration.
Furthermore, room temperature in laboratory was not
constant during the experiment. Room temperature is one of the degrees of
freedom and will affect the formation of the system and the pattern of curve.
The contaminated apparatus may affect the results as
well. The glass wares were not completely dried after washing will cause slight
dilution of the mixture.
One of the precautions is the same person should observe
all the cloudiness of mixture every time throughout the experiment. The
observer should make sure the eyes are perpendicular to the lower meniscus of
the liquids to avoid parallax error. The volatile liquids should be poured
immediately from the container to the conical flasks to minimise loss of
volume. The room temperature must be consistent. The apparatus must be clean
and dry to avoid contamination. The mixture should be well agitated then
allowed to attain equilibrium.
CONCLUSION
Ethanol, toluene and water is one of the
ternary system that is the phase diagram represent in the form of triangle.
Experiment was done by mixing ethanol and toluene and then titrated with water.
From the data obtained, we can see that as higher percentage of ethanol
compared to to percentage of toluene, the volume of water needed to achieve
cloudiness was higher. When cloudiness was observed, this means that two phase system establised.
At first part, toluene and water form partially miscible liquid and the
presence of sufficient amount of ethanol has produced a single liquid phase.
This indicate that ethanol managed to increased miscibility of the two
components until more water added and break the homogenity. The two phase
system only shown if the water added exceed the theoritical percentage where
the three components are partially miscible. Data also shows that, when
percentage of toluene is higher compared to ethanol, only small amount of water
needed to break the homogenity.
REFERENCES
1. A.T. Florence, D. Attwoo, Physicochemical Principles
of Pharmacy, 4th edition, 2006, Macmillan Press Ltd
3.
Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical
Sciences, by Martin, A.N.
It was very useful
ReplyDelete