Experiment 1
Part
A: Determination Of Phase Diagram For
Ethanol/Toluene/Water System Theory
Objective:
To
determine the phase diagram for the ethanol/toluene/water system
Introduction:
Ternary phase diagram is used to determine the
composition of three components in a system or phase at a constant pressure and
temperature. In this experiment, three components; ethanol, toluene and water
exist as a phase. By using the percentage of each component based on their
volume when the second phase starts to appear and the temperature, the ternary
phase diagram is plotted.
There are three coordinates from the
phase diagram where each apex represent 100% composition of each component.
Take the following phase diagram for example, each side of the triangle
represents a binary mixture where two components mixed together and any line
drawn parallel to one of the sides shows the percentage of a particular
component. For example, line FG means there are 50% of B. the intercept point
K, showing that there are combination of 20% of A, 50% of B and 30% of C.
The mutual solubility of binary solution differs
when there are different components added and mixed together. If the third
component is more soluble in one of the liquids than in the other, then the
miscibility between that pair of liquids decreases. But, if the third component
is soluble in both components, then the mutual solubility will increase. In the
experiment, water as the third component is added to the mixture of ethanol and
toluene.
Apparatus:
Burette,
Retort stand, Conical flask, Measuring cylinder and Test tube
Materials :
Ethanol,
Toluene and Distilled water
Method
1. The
experiment to determine the phase diagram for ethanol/toluene/water system is
done twice.
2. The
mixture of ethanol and toluene is prepared in a sealed container measuring
100cm3 that contains percentage of ethanol (in percent):10, 25, 35,
50, 65, 75, 90 and 95.
3. 20
mL of each mixture is prepared by filling a certain volume using burette
accurately.
4. Each
mixture is titrated with water until cloudiness is observed due existence of a
second phase.
5. A
small amount of water is added and after each addition it is shaken well.
6. Room
temperature is measured.
7. The
percentage is calculated based in the volume of each component when second phase starts to appear/separate.
8. The
points are plotted onto a triangular paper to give triple phase diagram at the
recorded temperature.
9. A
few more measurement is done if necessary.
10. The
diagram is discussed in the discussion.
Results:
Room
temperature: 28ﹾC
1st
time titration
Vial
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Ethanol
|
2
|
5
|
7
|
10
|
13
|
15
|
18
|
19
|
Toluene
|
18
|
15
|
13
|
10
|
7
|
5
|
2
|
1
|
Initial
volume of burette (mL)
|
3.40
|
3.40
|
4.00
|
4.70
|
7.00
|
9.30
|
13.40
|
24.00
|
Final
volume of burette (mL)
|
3.40
|
4.00
|
4.70
|
6.10
|
9.30
|
13.40
|
24.00
|
39.50
|
Volume
of water used (mL)
|
0.00
|
0.60
|
0.70
|
1.40
|
2.30
|
4.10
|
10.60
|
15.50
|
2nd
time titration
Vial
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Ethanol
|
2
|
5
|
7
|
10
|
13
|
15
|
18
|
19
|
Toluene
|
18
|
15
|
13
|
10
|
7
|
5
|
2
|
1
|
Initial
volume of burette (mL)
|
1.40
|
1.40
|
1.70
|
2.30
|
3.50
|
5.60
|
8.70
|
18.80
|
Final
volume of burette (mL)
|
1.40
|
1.70
|
2.30
|
3.50
|
5.60
|
8.70
|
18.80
|
34.40
|
Volume
of water used (mL)
|
0.00
|
0.30
|
0.60
|
1.20
|
2.10
|
3.10
|
10.10
|
15.60
|
Vial
|
Volume of water used (mL)
|
Average of water used (mL)
|
|
I
|
II
|
||
1
|
0.00
|
0.00
|
0.00
|
2
|
0.60
|
0.30
|
0.45
|
3
|
0.70
|
0.60
|
0.65
|
4
|
1.40
|
1.20
|
1.30
|
5
|
2.30
|
2.10
|
2.20
|
6
|
4.10
|
3.10
|
3.60
|
7
|
10.60
|
10.10
|
10.35
|
8
|
15.50
|
15.60
|
15.55
|
Calculation:
Vial
|
Percentage (%)
|
||
Ethanol
|
Toluene
|
Water
|
|
1
|
10.0
|
90.0
|
0.0
|
2
|
9.8
|
88.0
|
2.2
|
3
|
24.2
|
72.6
|
3.1
|
4
|
32.9
|
61.0
|
6.1
|
5
|
45.0
|
45.0
|
9.9
|
6
|
55.1
|
29.7
|
15.3
|
7
|
49.4
|
16.5
|
34.1
|
8
|
50.6
|
5.6
|
43.7
|
Discussion:
Ternary phase diagram is known as three component system. The three binary systems for the three components need to be determined in order to construct a ternary diagram. Ternary diagrams also have a vertical temperature axis. Basically, the ternary diagram may represent 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 also transformed into an equilateral triangle to facilitate presentation and interpretation. In addition, each apex on the triangle representing the ternary system represents 100% of the component at that apex. For the side of the triangle which is 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. For experimentally studied ternary systems, the liquids surface may contour with the temperature interval representing the contour interval. Furthermore, the 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 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.
Water and toluene will form a two-phase system in this experiment because they are slightly miscible. The heavier phases are formed when water saturated with toluene, while the lighter phase is formed when toluene saturated with water. However, ethanol is miscible with both toluene and water completely. Hence, the addition of sufficient amount of ethanol to the toluene-water system would produce a single liquid phase. This indicated all the three components are miscible and the homogenous mixture is formed. It is shown in the triple phase diagram that had been plotted on triangular diagram.
A binodal curve is obtained after plotting the graph. In thermodynamics, the binodal is known as the coexistence curve or binodal curve which denotes the condition at which two distinct phases may coexist. Equivalently, it is the boundary between the set of conditions in which it is thermodynamically favorable for the system to be fully mixed and the set of conditions in which it is thermodynamically favorable for it to phase separate. In general, the binodal is defined by the condition at which the chemical potential of all solution components is equal in each phase. The extremum of a binodal curve in temperature coincides with the one of the spinodal curve and is known as a critical point. For this experiment, the region bounded by the curve is two phase region while the region that is not bounded by the curve is one phase region.
During this experiment, some errors are occurred which lead to inaccuracy of the experiment. First and foremost, the mixture was poured into the conical flask may contain some water droplets because the conical flask was not yet dry completely after washing. The eye level of experimenter was not perpendicular to the bottom of meniscus of measuring cylinder when measuring the volume of the toluene and ethanol. The mixture does not shake well during titration. Besides, judgement of experimenter may be different in determining the cloudiness of the mixture of ethanol and toluene with water. There were two to three drops of water came out in the burette although it was tighten. The error in the burette may slightly cause the difference in the readings of volume of water.
During this experiment, some errors are occurred which lead to inaccuracy of the experiment. First and foremost, the mixture was poured into the conical flask may contain some water droplets because the conical flask was not yet dry completely after washing. The eye level of experimenter was not perpendicular to the bottom of meniscus of measuring cylinder when measuring the volume of the toluene and ethanol. The mixture does not shake well during titration. Besides, judgement of experimenter may be different in determining the cloudiness of the mixture of ethanol and toluene with water. There were two to three drops of water came out in the burette although it was tighten. The error in the burette may slightly cause the difference in the readings of volume of water.
Due to the presence of errors, some precautions need to be carried out. The experimenters have to wear glove to protect their hands from any unnecessary injury. The eye level of experimenter must perpendicular to the bottom of meniscus of measuring cylinder for every measurement. The apparatus that cleaned with distilled water need to be dried with tissue paper. Moreover, the mixture need to be shook well for every addition of water. The titration should be carried out by only the same experimenter to reduce the errors. The water need to be dropped one by one when the mixture approached to turn cloudy, so that the last drop of water that made the mixture to turn cloudy can be determined. The experiment can be carried out several times more and find out the average reading of the volume of water which will increase the accuracy of the experiment.
The graph received from this experiment does not provide a perfect binodal graph. This is due to the errors found in the result, received by doing the experiment. The last result from the experiment might have errors due to the mistakes stated in the paragraph before.
Questions:
Does the mixture containing 70% ethanol, 20% water and 10% toluene (volume) appear clear or does it form two layers?
The graph received from this experiment does not provide a perfect binodal graph. This is due to the errors found in the result, received by doing the experiment. The last result from the experiment might have errors due to the mistakes stated in the paragraph before.
Questions:
Does the mixture containing 70% ethanol, 20% water and 10% toluene (volume) appear clear or does it form two layers?
The mixture containing 70% ethanol, 20% water and 10% toluene does appear clear and show as one
liquid phase from the graph plotting.
What will happen if you dilute 1 part of the mixture with 4 parts 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 = 1 x (20/100) = 0.2 part of water
1 part mixture x 10% toluene = 1 x (10/100) = 0.1 part of toluene
Hence, the mixture contains 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
Ethanol = (0.7/5) x 100% =14%
Water = [(0.2+4)/5] x 100% = 84%
Toluene = (0.1/5) x 100% =2%
Therefore, from the phase diagram, this mixture is not under the area of the binomial curve and one phase is formed.
(b) Toluene: 1 part of mixture + 4 parts of toluene
Ethanol = (0.7/5) x 100% =14%
Water = (0.2/5) x 100% = 4%
Toluene = [(0.1+4)/5] x 100% =82%
Therefore, from the phase diagram, this mixture is under the area of the binomial curve and a two liquid phase of solution is formed.
(c) Ethanol: 1 part of mixture + 4 parts of ethanol
Ethanol = [(0.7+4)/5] x 100% =94%
Water = (0.2/5) x 100% = 4%
Toluene = (0.1/5) x 100% =2%
Toluene = (0.1/5) x 100% =2%
Therefore, from the phase diagram, this mixture is not under the area of the binomial curve and one phase is formed.
(b) Toluene: 1 part of mixture + 4 parts of toluene
Ethanol = (0.7/5) x 100% =14%
Water = (0.2/5) x 100% = 4%
Toluene = [(0.1+4)/5] x 100% =82%
Therefore, from the phase diagram, this mixture is under the area of the binomial curve and a two liquid phase of solution is formed.
(c) Ethanol: 1 part of mixture + 4 parts of ethanol
Ethanol = [(0.7+4)/5] x 100% =94%
Water = (0.2/5) x 100% = 4%
Toluene = (0.1/5) x 100% =2%
Therefore, from the phase diagram, this mixture is above the area of the binomial curve. Therefore, a one liquid phase of solution is formed.
Conclusion:
According
to the experiment, volume of water added to the mixture of ethanol and toluene
increases proportional to percentage of ethanol and inversely proportional to
the percentage of toluene. The change from a phase to another could be observed
from the mixture cloudiness as the flask is swirled. The system or the solution
will separate into two phase. Water and toluene form a two-phase system because
they are only slightly miscible while Ethanol is completely miscible with both
toluene and water. The phase composition could be observed from the
intersection line in the triangular diagram.
Reference:
Reference:
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