Determination of Phase Diagram for
Ethanol/ Toluene/ Water System Theory Three-Component Systems
Date:
15th April 2014
Title:
Determination of Phase Diagram for Ethanol / Toluene / Water System
Objectives:
To determine the phase diagram of three-component systems which is ethanol, toluene and water.
Introduction:
The above triangular
diagram is use to plot the composition for the three-component systems at
constant temperature and pressure. There are about five rules relating to the
use of a three-phase diagram which are:-
1. Each
of three corners or apexes of the triangle represent 100% by weight of one
component (A, B, or C) and 0% of the other two components.
2. The
three lines joining the corner points represent two-component mixtures of the
three possible combinations of A, B and C. thus the lines AB, BC and CA are
used for two component mixtures of A and B, B and C, and C and A.
3. The
area within the triangle represents all the possible combinations of, A, B,
and C to give three-component systems.
4. If
a line drawn through any apex to appoint on the opposite side, then all
systems represented by points on such a line have a constant ratio of two
components, in this case A and B for line DC.
5. Any
line drawn parallel to one side of the triangle represents ternary systems in
which the proportion of one component is constant. In this instance, all
systems prepared along HI will contain 20% of C and different concentrations
of A and B.
The mutual solubility of the miscible
liquids can change by the addition of a third component. If this third
component is more soluble in either one from the two components, the
solubility of both components will reduce. But if the third component is
soluble in both components at the same time, the solubility increases. Thus,
when ethanol is added into a mixture of benzene and water, the solubility of
these two components will increase until a point is reached, where the
mixture become homogenous. This application can be used in formulations of
solutions. Examples of three-component liquid system that have been tested
are castor oil / alcohol / water, peppermint oil / propylene glycol / water,
peppermint oil / polyethylene glycol / water.
By
having the understanding of the triangular phase diagram, we can predict what
will happen to the system when it is diluted. This experiment is to determine
the phase diagram for ethanol / toluene / water system.
Apparatus : Conical flaks, Measuring cylinder, Burette, Retord stand
Materials : Ethanol, Toluene, Distilled water |
Procedure:
1. Different compositions
of ethanol and toluene mixtures were prepared and placed in sealed conical
flasks.
2. Each
mixture contained different % volume of ethanol in 50ml at 10, 25, 35, 50,
65, 75, 90, 95% v/v.
3. A
burette was filled with distilled water.
4. The
mixtures were titrated with water, accompanied by vigorous shaking of the
conical flask.
5. A
cloudy mixture was formed and titration was stopped.
6. The
volume of the water used was recorded.
7. Steps
1 – 6 were repeated to do a second titration. The volume of water required
for complete titration of each mixture was recorded.
8. The
average volume of water used was calculated.
9. Percentage
volume of each component of the ternary system for when a second phase became
separated was calculated.
10. All data were plotted on a graph paper with
triangular axes to produce a triple phase diagram.
|
Results:
Ethanol
(%v/v)
|
Toluene
(%v/v)
|
Volume of water used
(mL)
|
Average volume of
water used (mL)
|
|||
Titration I
|
Titration II
|
|||||
Initial
|
Final
|
Initial
|
Final
|
|||
10
|
90
|
1.00
|
1.30
|
1.30
|
1.60
|
0.30
|
25
|
75
|
1.60
|
2.40
|
2.40
|
3.20
|
0.80
|
35
|
65
|
14.20
|
15.10
|
15.10
|
16.30
|
1.05
|
50
|
50
|
16.30
|
18.00
|
18.00
|
19.90
|
1.80
|
65
|
35
|
19.90
|
22.60
|
22.60
|
25.20
|
2.65
|
75
|
25
|
25.20
|
29.20
|
29.20
|
33.40
|
4.10
|
90
|
10
|
33.40
|
43.70
|
13.70
|
23.50
|
10.05
|
95
|
5
|
23.50
|
40.70
|
20.10
|
37.30
|
17.20
|
Calculation:
Total volume (mL) (Average water + 20mL)
|
Ethanol
|
Toluene
|
Water
|
|||
Volume (mL)
|
%(v/v)
|
Volume (mL)
|
%(v/v)
|
Volume (mL)
|
%(v/v)
|
|
20.30
|
2.00
|
9.85
|
18.00
|
88.67
|
0.30
|
1.48
|
20.80
|
5.00
|
24.04
|
15.00
|
72.12
|
0.80
|
3.84
|
21.05
|
7.00
|
33.25
|
13.00
|
61.76
|
1.05
|
4.99
|
21.80
|
10.00
|
45.87
|
10.00
|
45.87
|
1.80
|
8.26
|
22.65
|
13.00
|
57.40
|
7.00
|
30.90
|
2.65
|
11.70
|
24.10
|
15.00
|
62.24
|
5.00
|
20.75
|
4.10
|
17.01
|
30.05
|
18.00
|
59.90
|
2.00
|
6.66
|
10.05
|
33.44
|
37.20
|
19.00
|
51.08
|
1.00
|
2.69
|
17.20
|
46.23
|
Graph:
Question
1. Does the mixture containing 70% ethanol,
20% water and 10% toluene (volume) appear clear or does it form two layers?
A
clear solution will appear and form one liquid phase.
2. What will happen if you dilute 1 part of
the mixture with 4 parts of:-
a) Water
Two phases will be observed
b) Toluene
Two phases will be observed
c) Ethanol
One phase will be observed
Discussion
The presence of third
liquid component can sometimes be very useful in changing the mutual solubility
of two other components. In this case, we can add a third component that will
make the other two components less soluble in each other.
Solubilities for three
component liquid mixtures are covalently displayed on an equilateral triangle.
Each vertex of the triangle represents a pure component. Thus, the top vertex
represent pure component of ethanol, the right vertex represents pure toluene
and the left vertex represent the pure component of water.
Each of the three slides
of triangle represents a binary (two-component) mixture. For example, the right
side of the triangle represents mixtures of ethanol and toluene, the left side
represents mixtures of ethanol and water, and the base represents mixtures of
water and toluene. Inside the triangle, we have mixtures containing all three
components.
This experiment was
carried out at constant temperature and pressure. In this experiment,
increasing weight of water has been added to a constant weight mixture of
toluene and ethanol.
Along the phase boundary only
one variable is required. Water and toluene form a two-phase system because
they are only slightly miscible. Ethanol
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.
In a solution containing
10% ethanol and 90% toluene, an average of 0.3mL of water was added for a
second phase to occur. The percentage of each component now is 9.85% ethanol,
88.67% toluene and 1.48% of water. These are represented by a point on
triangular diagram.
In the solution containing
25% ethanol and 75% toluene, an average 0.80mL of water was added for a second
phase to occur. The percentage of each component now is 24.04% ethanol, 88.67%
toluene and 3.84% of water.
In the solution containing
35% ethanol and 65% toluene, an average 1.05mL of water was added for a second
phase to occur. The percentage of each component now is 33.25% ethanol, 61.76%
toluene and 4.99% of water.
In the solution containing
50% ethanol and 50% toluene, an average 1.80mL of water was added for a second
phase to occur. The percentage of each component now is 45.87% ethanol, 45.87%
toluene and 8.26% of water. As we can see here, the percentage of ethanol and
toluene are same.
In the solution containing 65% ethanol and 35%
toluene, an average 2.65mL of water was added for a second phase to occur. The
percentage of each component now is 57.40% ethanol, 30.90% toluene and 11.70%
of water.
In the solution containing
75% ethanol and 25% toluene, an average 4.10mL of water was added for a second
phase to occur. The percentage of each component now is 62.24% ethanol, 20.75%
toluene and 17.01% of water.
In the solution containing 90% ethanol and 10%
toluene, an average 10.05mL of water was added for a second phase to occur. The
percentage of each component now is 59.90% ethanol, 6.66% toluene and 33.44% of
water.
In the solution containing
95% ethanol and 5% toluene, an average 17.20mL of water was added for a second
phase to occur. The percentage of each component now is 51.08% ethanol, 2.69%
toluene and 46.23% of water.
For overall, we can see
here that the percentage of ethanol and water are keep increasing meanwhile the
concentration of toluene is decreasing. That’s mean the presence of water have changed
the mutual solubility between ethanol and toluene.
However, in this experiment the
binomial curve is incomplete. This may be due to some errors. Firstly, the
measured volume of ethanol and toluene are less than the actual value. Ethanol and toluene are volatile liquids and
they will vaporize if left longer. Some of them already evaporated and thus
affected the volume of water needed for titration. Secondly, parallax errors
may occur during the experiment. The eyes of the observer is not perpendicular
to the meniscus of the liquids. This caused inaccurate measurement of liquids
and thus affecting the curve. Next, the cloudiness was hard to be judged
because there was no specific range of degree of cloudiness in each of the
experiment. This might affect the volume of water added to the solution and has
greatly affected the percentage by volume and the curve too. Also, the
temperature in the laboratory that was not constant. Temperature will change
the curve pattern and this might be the cause of incomplete binomial curve. The
contaminated apparatus may affect the results obtained.
Therefore, precaution steps need
to be taken. The volatile liquids must be used immediately when poured
from the container as to avoid loss of volume of liquids. The eye of the
observer must in perpendicular to the meniscus of the liquids to avoid parallax
error to obtain accurate volume of liquids. We can choose the same student to observe
the cloudiness throughout the experiment so that the results will be more
accurate. The room temperature must be consistent. The apparatus must be
cleaned before using them.
Conclusion
The phase diagram for
ethanol / toluene / water system can be determined by using triangular diagram.
Ethanol, toluene and water system is ternary system with one pair of partially
miscible liquid (toluene and water)
Reference
Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical
Sciences, by Martin, A.N.
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