To determine the phase diagram for ethanol/toluene/water system.
Introduction:
Ternary phase
diagrams are 3 component systems. To construct a ternary diagram it is
necessary to know the three binary systems for the three components. Ternary
diagrams have a vertical temperature axis.
The actual
ternary diagram may be represented as a three dimensional form or more commonly
as a two dimensional projection of the liquids surface onto the base of the
triangle created when the three binary diagrams are joined together. This
irregular triangle is often transformed into an equilateral triangle to
facilitate presentation and interpretation.
For
experimental studies on ternary systems the liquids surface may be contoured
with the temperature interval representing the contour interval. The fields
indicated on the ternary diagram represent the primary phase fields, of solid
phases in equilibrium with liquid, present on the liquids surface.
Straight lines
which join the composition points of two phases whose primary phase fields
share a common boundary curve are called Alkemade Lines. Thus the edges of the
triangle are Alkemade Lines as they join the individual phases AB, AC and BC,
which share a boundary curve. Alkemade lines are a specific type of tie line.
The phase
relates the number of phases present in the system, the number of components
which define the system and the degrees of freedom displayed the by the system
at equilibrium.
Phase
Rule:
P +
F = C + 1
All
compositions, e.g., bulk compositions, liquid compositions and compositions of
solid phases on ternary diagrams are expressed in terms of the three end
member components which define the system. These three components are located
at apex of the triangle.
Each apex on the
triangle of the ternary system represents 100% of the component at
that apex. The side of the triangle, directly opposite the apex, represents 0%
of the apex component. Compositions of points which lie along the outside edge
of the triangle are simply a mixture of the two components at each end of the
tie line, with 0% of the third component.
The composition
of points which lie inside the area of the triangle can be determined using the Triangular Grid or Two Lines method. In this experiment, we will focus
on Triangular Grid method.
Triangular Grid
method:
In this method a
grid is constructed on the diagram. This grid is most commonly set up
representing a 10% incremental increase in the components. To determine the
composition of a point within the triangular area of the diagram a series of
three lines are drawn through the point of intersect, with each line parallel
to a side of the triangle. With these lines in place the percentage of each
component in the composition of the point can readily be determined.
Figure 1: Example of a Triangular Grid
Chemicals:
 |
| Toluene |
 |
| Distilled water |
 |
| Ethanol |
Apparatus:
 |
| Measuring Cylinder |
 |
| Retort Stand |
 |
| Burette |
 |
| Conical Flask |
Procedures:
100cm3 mixtures of ethanol and
toluene were prepared in sealed
containers containing the following percentages (%) of ethanol :10, 25, 35, 50, 65, 75, 90 and 95. 20m1 of each mixture is prepared using a burette. Each mixture is titrated with
water until cloudiness is observed due to existence of second phase.
A little water was
added and shaken well after each addition. The percentage was calculated based
on the volume of each component when the second phase started to
appear/separate. A triple phase diagram is plotted based on the percentage of the components at the recorded temperature. The experiment is repeated
for more accurate reading.
Results
Table
1:
Component/
Volume(cm3)
|
||||||||
Ethanol
|
2.0
|
5.0
|
7.0
|
10.0
|
13.0
|
15.0
|
18.0
|
19.0
|
Toluene
|
18.0
|
15.0
|
13.0
|
10.0
|
7.0
|
5.0
|
2.0
|
1.0
|
Water (first experiment)
|
0.2
|
0.5
|
0.9
|
1.7
|
2.5
|
4.6
|
12.0
|
18.6
|
(second experiment)
|
0.1
|
0.8
|
0.7
|
1.4
|
2.7
|
4.2
|
9.7
|
16.1
|
(average)
|
0.2
|
0.7
|
0.8
|
1.6
|
2.6
|
4.4
|
10.9
|
17.4
|
Table
2:
Component/ Percentage (%)
|
||||||||
Ethanol
|
9.90
|
24.15
|
33.65
|
46.3
|
57.52
|
61.48
|
58.25
|
50.80
|
Toluene
|
89.11
|
72.46
|
62.5
|
46.3
|
30.97
|
20.49
|
6.47
|
2.67
|
Water
|
0.99
|
3.38
|
3.85
|
7.41
|
11.50
|
18.03
|
35.28
|
46.52
|
Discussion
Ternary phase
diagram contains three components which are water, ethanol and toluene. In this
experiment, the mixture of ethanol and toluene once sealed in measuring
container containing various percentages of ethanol and toluene. The mixture is
prepared into 20mL of each containing various percentages of ethanol such as
(%) 5,50,60,75,90. The mixture is titrated with water
until cloudiness appear due to existence of second phase. This means two
phases present in this experiment is detected and the volume of water used
until the cloudiness is appears is recorded.
Based on the graph, each three
corners or apexes of triangle represent 100% by volume of one component (water,
ethanol and toluene). As a result, that same apex will represent 0% of another two
components. When the percentages of ethanol increases in the mixture, the
volume of water need to be titrated until the mixture turn cloudiness is
increases. The addition of water as the third component to a pair of miscible
liquids of toluene and ethanol can change their mutual solubility. If the third
component is more soluble in one of the two different component mixtures the
mutual solubility of the liquid pair is decreased and thus two phases liquids
will be appears.
Toluene and ethanol are miscible liquids while toluene is
water insoluble liquid while ethanol contains OH group that will completely
react with water as water is a polar substance that will attract OH group.
Hence water and ethanol will be miscible in any amount. Hence, two phases diagram
is appears due to decrease the solubility of the three components mixture.
During the experiment there are some errors that may happen. While taking the
measurements of the liquids, the eyes does not perpendicularly on the scale of
the measuring cylinder. Hence the eyes must be perpendicular to the scale of
the to prevent the false measurement of the liquids. Other than that, when
undergo shaking process during titrating to make the mixture completely
miscible, the shaking process does not undergo gently and it may affect the
person to take the actual amount of water needed to make the mixture cloudiness
hence while titrating , the shaking process must undergo gently and the actual
volume of water can be recorded.
Other than that, the errors is the degree
of cloudiness. We do not have a specific range of degree of cloudiness in each
of the experiment. This might affect the volume of water added to the solution.
It may be less or more than the actual one. This has greatly affected the
percentage by volume and the curve too.
Besides, room temperature in the laboratory
that is not constant during the experiment is one of the errors too. Room
temperature is one of the significant factors that will change the graph or
curve pattern and this might be the cause of incomplete binomial curve.
Moreover, volatility of the liquids that we
used for the experiment. We use ethanol and toluene which are volatile liquids
and they will vapourise if left longer. If this happened, the measured volume may
be less than the actual one as some of them already evaporates and thus
affected the volume of water needed for titration. Thus we should not leave the measured toluene and ethanol too long and conduct the experiment quickly.
1. Does the mixture
containing 70% ethanol, 20% water and 10% toluene (volume) appear clear
or does it form two layers?
or does it form two layers?
Based on
the diagram that has been plotted, it can be examined that the mixture
containing 70% ethanol,
20% water and 10% toluene will be appeared as a clear solution.
20% water and 10% toluene will be appeared as a clear solution.
2. What will happen if you dilute 1 part of the mixture with 4 parts of
(a)
Water
The solution appeared in two layers as there are two
phases formed.
(b) Toluene
The solution appeared in two layers as there are two
phases formed.
(c)
Ethanol
The solution appeared in one layer as there is only
single phase formed.
2. http://www.sjsu.edu/faculty/selvaduray/page/phase/ternary_p_d.pdf
3 .http://sig.ias.edu/files/Ternary%20Phase%20Diagrams.pdf
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