PART A
TITLE:
Determination of Phase Diagram for Ethanol/ Toluene/ Water System Theory
Three-Component Systems
DATE
OF EXPERIMENT:
3rd November 2014
OBJECTIVES:
(i)
To become familiar with certain ‘rules’
that relate to the use of triangular coordinates to know the mutual solubilities of liquids in
a two-phase system
(ii)
Determination of the solubility limits
in a ternary system 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)
INTRODUCTION:
In making
pharmaceutical formulation often multiple component need to be mixed together
and need to be in homogeneous form. This is usually possible by knowing the
exact ratio of each component to be mixed with regard of some other condition
such as temperature. In this experiment, there are three components of concern
which were ethanol, toluene and water. Water is insoluble in toluene, but as it
were mixed together with ethanol, all three components can achieve homogeneous
solution at equilibrium if proper proportion was used.For 3 component systems
at constant temperature and pressure, the compositions may be stated in the
form of coordinates for a triangular diagram.
Each side of a triangular diagram correspond
one of the three component in the system and can be divided into part to
produce equilateral grids as shown above. Thus any point in the diagram will
show the amount of all three components while a point on the sides will show
amount of any two components with each apex represent an amount of 100% of any
one of the three components. In this experiment, the pressure is considered fixed at 1
atm, and so the number of degrees of freedom becomes three.
The three lines joining the corner
points represent two-component mixture of the three possible combinations of A,
B and C. By dividing each line into 100 equal units, the location of a point
along the line can be directly related to the percent concentration of one
component in a two-component system. The area within the triangle represents
all the possible combinations of A, B and C to give three-component system.
Line AC , opposite apex B represent system containing A and C (B=0). The
horizontal lines running across the triangle parallel to AC denote increasing
percentages of B from B=0 (on line AC) to B=100 (at point B). Line drawn
parallel to one side of the triangle represents ternary system in which the
percent by weight of one component is constant.
Consider
a three-component system consisting of liquids A, B and C. A and B are
immiscible with each other while C is miscible with both. A mixture of A and B
at equilibrium will exist as two physically distinct phases. The addition of C
will markedly increase the mutual solubility of A and B such that at a certain
concentration of C. The mixture will become homogenous. Conversely, a mixture
of A and C will exist as a homogenous phase at equilibrium. The addition of the
third component will markedly reduce the mutual solubility of A and C such that
at a particular concentration of the third component, the mixture will separate
out into two phases. Examples of three-component systems that
has been studied include castor oil/ alcohol/ water; peppermint oil/ propylene
glycol/ water; peppermint oil/ polyethylene glycol/ water.
APPARATUS:
Beaker, burette, pipette, conical flask, measuring
cylinder,dropper,retort stand
MATERIAL:
Toluene,distilled water, ethanol
EXPERIMENTAL PROCEDURES:
1) Mixtures
of ethanol and toluene were prepared in sealed containers measuring 100cmᵌ
containing the following percentages of ethanol: 10%, 25%, 35%, 50%, 65%, 75%,
90%, 95%
2) 20ml
of each mixture was prepared by filling a certain volume using a burette.
3) Each mixture was triturated with water until
cloudiness was observed due to the existence of a second phase
4) A
little water was added and shaken well after each addition.
6) The
room temperature was measured using the thermometer.
7) The
percentage based on the volume of each component was calculated when the second
phase starts to appear.
8) The
points were plotted onto a triangular paper to give a triple phase diagram at
the recorded temperature. One more measurement was done if necessary.
TABLE OF RESULT:
Titration with water
Conical flask
Volume
of water (mL)
|
A
|
B
|
C
|
D
|
E
|
F
|
G
|
H
|
First
Titration
|
6.20
|
1.10
|
1.35
|
1.90
|
2.75
|
3.90
|
10.50
|
16.90
|
Second
Titration
|
6.95
|
1.60
|
1.70
|
2.55
|
3.15
|
4.40
|
10.90
|
17.25
|
Average
Volume
|
6.58
|
1.35
|
1.53
|
2.23
|
2.95
|
4.15
|
10.70
|
17.08
|
The percentage of each components
Conical
Flask
|
Ethanol (%)
|
Total volume (water+ ethanol+ toluene)
(mL)
|
Ethanol
|
Toluene
|
Water
|
|||
Volume
(mL)
|
Percentage
(%)
|
Volume
(mL)
|
Percentage
(%)
|
Volume
(mL)
|
Percentage
(%)
|
|||
A
|
10
|
26.58
|
2.00
|
7.52
|
18.00
|
67.72
|
6.58
|
24.76
|
B
|
25
|
21.35
|
5.00
|
23.42
|
15.00
|
70.26
|
1.35
|
6.32
|
C
|
35
|
21.53
|
7.00
|
32.51
|
13.00
|
60.38
|
1.53
|
7.11
|
D
|
50
|
22.23
|
10.00
|
44.98
|
10.00
|
44.98
|
2.23
|
10.03
|
E
|
65
|
22.95
|
13.00
|
56.64
|
7.00
|
30.50
|
2.95
|
12.85
|
F
|
75
|
24.15
|
15.00
|
57.97
|
5.00
|
24.84
|
4.15
|
17.18
|
G
|
90
|
30.70
|
18.00
|
58.63
|
2.00
|
6.51
|
10.70
|
34.85
|
H
|
95
|
37.08
|
19.00
|
51.24
|
1.00
|
2.70
|
17.08
|
46.06
|
GRAPH:
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DISCUSSION:
The
phase diagram for ternary system is usually represented in a triangular
diagram. The graph plotted in the triangular diagram accounts for the fact that
only two variables are required. Along the phase boundary only one variable is
required. Each of the three corners or apexes of the triangle represent 100% by
volume of one component (ethanol, toluene and water). So, each apex will
represent 0% of the other two components. The real curve was determined in this experiment.
Due to slightly miscibility, the water and toluene will form a two-phase
system. For ethanol, it is completely miscible with both toluene and water. Thus, the addition of
sufficient amount of ethanol to the toluene-water system would produce a single
liquid phase in which all the three components are miscible and the mixture is
homogenous.
However, for this experiment we do it in
another way, that is, the addition of water into toluene-ethanol system. The
curve of the plotted graph is termed as binomial curve. The peak of the curve
is at which the ethanol is 60% by volume. The region under the curve shows that
the presence of two phases that is water and toluene whereas the region above
the curve boundary which is the unbound region shows one phase of homogenous
solution. The bounded region is actually between the binomial curve and the
line of toluene and water mixture. Ethanol which acts as surfactant allow the
two phase solution to become one phase solution.
The points at both ends of the curve are the
limits of solubility of toluene in water and water in toluene. Along the
toluene-water line, which represents a binary mixture of toluene and water, the
liquids are able to form a homogenous mixture as long as the first point is not
exceeded. However, the second point must be exceeded for a homogenous mixture
to be formed. The length of line between the two points represents the mixture
of toluene and water with such composition that they cannot form a homogenous
mixture. This may be due to insolubility of toluene in water or water in
toluene.
From the graph plotted, the binomial curve is
incomplete as the points are deviated a bit from theoretical points and no tie
line is obtained as there may be some errors during the experiment. Firstly,
the glass wares are contaminated. So, the precaution step taken is we must
rinse the glass wares and then wiped and dried the glass wares before used. The
presence of distilled water in the glass wares when we mixed toluene and
ethanol will cause the immediate of cloudiness observed and this cause the
result to be inaccurate. Secondly, there is no specific range for the degree of
cloudiness. This might greatly affect the volume of water added to the solution
and causing the volume to be less than or more than the theoretical. As a
result, the percentage by volume of each component and the curve are affected. The
way to overcome this error is by fixed a consistent range of cloudiness for
each set of the experiment or we use the same person to conduct the set of
experiment so that he or she could compare the cloudiness he or she made
before.
Next, there is vaporization of liquid
occurred. As we know that, ethanol and toluene are volatile liquid and easily
vaporized. When some liquid vaporized, the measured volume will be less and
affect the volume of water that needed for the titration. So, the volatile
liquid must be mixed and used immediately when they are poured out from the
container to avoid the loss of the measured volume. Parallax error was occurred
when we measured and read the volume of the liquid from the measuring cylinder
and burette. To avoid this from happening, the eye level of the observer must
be in perpendicular to the meniscus of the liquids in the measuring apparatus
to obtain accurate volume of the liquids. Lastly, inconsistency of room
temperature during the experiment will affect the result too because
temperature is one of the factor to determine graph pattern and phase diagram.
Therefore, we have to conduct the experiment under the room temperature which
is consistent to avoid the deviation of the final result.
PRACTICE:
1) Does the mixture containing 70% ethanol, 20%
water and 10% toluene (volume) appear clear or does it form two layer?
The mixture containing 70% ethanol, 20% water
and 10% toluene (volume) is not line within the region of the graph plotted but
above the graph plotted, so it appeared clear as single phase solution.
2) What will happen if you dilute 1 part of the mixture with 4
parts of (a) Water (b) toluene (c) ethanol?
1 part of the mixture:
70% ethanol = 0.7 part ethanol of whole mixture
20% water = 0.2 part water of whole mixture
10% toluene = 0.1 part toluene of whole mixture
(a)
1 part of mixture + 4 parts of water:
Ethanol = 0.7 x 100% =14%
1+4
Water = 0.2+4 x 100% = 84%
1+4
Toluene = 0.1 x 100% =2%
1+4
For
14% ethanol, 84% water, 2% toluene, it does not lie within the area bounded by
the graph, so the solution appeared clear and as single phase liquid solution.
(b)
1 part of mixture + 4 parts of toluene
Ethanol = 0.7 x 100% =14%
1+4
Water =0.2 x 100% = 4%
1+4
Toluene = 0.1+4 x 100% =82%
1+4
For
14% ethanol, 4% water, 82% toluene, it does not lie within the area bounded by
the graph, so the solution appeared clear and as single phase liquid solution.
(c)
1 part of mixture + 4 parts of ethanol
Ethanol = 0.7+4 x 100% =94%
1+4
Water = 0.2 x 100% = 4%
1+4
Toluene = 0.1 x 100% =2%
1+4
For
94% ethanol, 4% water, 2% toluene, it does not lie within the area bounded by
the graph, so the solution appeared clear and as single phase liquid solution.
CONCLUSION:
The experiment of ternary system involves three different liquids which are ethanol, toluene, and water. This ternary system was representing in the form of triangular diagram. The data obtained from the experiment of mixing the ethanol and toluene and then triturated with water is the percentage of ethanol was much higher than the percentage of toluene and higher amount of water was needed to achieve cloudiness. The two phase system was established once the cloudiness was observed. The single liquid phase formed when toluene and water partially miscible and the ethanol in a sufficient amount. The presence of ethanol helps to increase the miscibility of toluene and water. Lastly, when water added exceed the theoretical percentage where the three components are partially miscible, the two phase systems occur.
REFERENCE:
1.
Physicochemical Principles of Pharmacy , 3rd edition
(1998) . A.T. Florence and D.Attwood. Macmillan Press Ltd.
2.
Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical
Sciences, by Martin, A.N.
4. Phase diagram of a
three-component partially immiscible liquid system : http://kimia.um.edu.my/physical/PHY_Chem_Year_3/Experiment%205.pdf
5.
Ternary
Phase Diagrams : http://www.tulane.edu/~sanelson/eens212/ternaryphdiag.htm
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