Experiment 1: Phase Diagrams (Part A); Determination of Phase Diagram for Ethanol/ Toluene/ Water System TheoryDate15 April 2014TitleDetermination of Phase Diagram for Ethanol/ Toluene/ Water System Theory
Objectives
1. To determine 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).
2. To construct the solubility curve of the system being studied on triangular diagram.
Introduction
In pharmaceutical formulation, often multiple components 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 and toluene is insoluble, but as it was mixed together with ethanol, all three components can achieve homogeneous solution at equilibrium if proper proportion was used.
This ternary system is represented by triangular diagram. Each side of a triangular diagram represent one of the three components 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 ratio of all three components while a point on the sides will show amount of ratio any two components with each apex represent an amount of 100% of ratio of any one of the three components.
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 degrees of freedom. The four degrees of freedom are temperature, pressure, and any two from the three component concentration.
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 degrees 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
Apparatus and Materials
1. Eight 100cm3 conical flask.
2. Burette
3. Toluene
4. Ethanol
5. Distilled water
Procedures
An amount of eight, 20 ml solution of toluene and ethanol were prepared in eight different 100cm3 conical flasks. Each flash were filled so that it contain 10%, 25%, 35%, 50%, 65%, 75%, 90% and 95% of ethanol with the rest was toluene. The conical flasks were labelled A, B, C, D, E, F, G and H respectively. Measuring these components was done by using a burette to make sure accuracy.
An amount of eight, 20 ml solution of toluene and ethanol were prepared in eight different 100cm3 conical flasks. Each flash were filled so that it contain 10%, 25%, 35%, 50%, 65%, 75%, 90% and 95% of ethanol with the rest was toluene. The conical flasks were labelled A, B, C, D, E, F, G and H respectively. Measuring these components was done by using a burette to make sure accuracy.
Each flask were then were titrated slowly with water and stop when cloudiness were observed which showed that second phase started to appear. The temperature was recorded as well. The data obtained were used to plot onto the triangular diagram.
Results
Table of Data
Percentage of ethanol (%)
|
Volume of ethanol(mL)
|
Volume of toluene (mL)
|
Volume of water used(mL) in 1st test
|
Volume of water used(mL) in 2nd test
|
Average volume of water used (mL)
|
10
25
35
50
65
75
90
95
|
3.0
6.0
7.0
10.0
13.0
14.0
17.0
18.0
|
18.0
15.0
14.0
10.0
7.0
5.0
2.0
1.0
|
0.3
0.9
1.0
1.8
2.8
4.5
10.8
14.8
|
0.6
0.7
1.2
2.2
3.2
4.7
9.0
15.2
|
0.45
0.75
1.10
2.20
3.00
4.60
9.90
15.0
|
Total volume of mixture(mL)
|
Ethanol
Volume Percentage
(mL) (%)
|
Toluene
Volume Percentage
(mL) (%)
|
Water
Volume Percentage
(mL) (%)
|
21.45
21.75
22.10
22.20
23.00
23.60
28.90
34.00
|
3.0 14.0
6.0 27.6
7.0 31.7
10.0 45.0
13.0 56.5
14.0 59.3
17.0 58.8
18.0 52.9
|
18.0 83.9
15.0 69.0
14.0 63.4
10.0 45.0
7.0 30.4
5.0 21.2
2.0 6.9
1.0 2.9
|
0.45 2.1
0.75 3.5
1.10 5.0
2.20 10.0
3.00 13.0
4.60 19.5
9.90 34.3
15.0 44.1
|
Data presented in triangular diagram.
Practice
1 .Does the mixture containing 70% ethanol, 20% water and 10% toluene (volume) appear clear or does it form two layers?
It appears in clear solution.
2. What will happen if you dilute 1 part of the mixture with 4 parts of
a. water : Two phases is formed
b. toluene : Two phases is formed
c. ethanol : The phase remains clear
a. water : Two phases is formed
b. toluene : Two phases is formed
c. ethanol : The phase remains clear
Discussion
Toluene is soluble in ethanol but not in water. But, as these three components were mixed until certain ratio, all three components become completely miscible. Firstly, this experiment is carried out by making a solution of ethanol and toluene which will be completely miscible and water is added where early it will make up two phase. As we continue to add more water until appropriate amount, it will result to one phase system.
Addition of water to the mixture of ethanol and toluene increases the mutual solubility of the liquid pair until at one point the mixture become homogenous. The region under the graph shows that there are two phase system form which consist of water and toluene since the solubility of water with toluene is less than that with ethanol. Meanwhile the region above the graph shows homogenous mixture.
When the data have been plotted it should have look something like below graph.
 |
A nice and complete binomial curve
|
The line which separate the single-phase system and the two-phase system were the point at which supposed to be obtained through this experiment. There are some errors that were formed when conducting this experiment which lead to this inaccuracy which include:
·The end point where the cloudiness disappearance were not properly observed.
·Different rate of agitation may influence the disappearance of cloudiness.
In order to get a better result in doing this experiment is by taking serious consideration to some precaution step. The precaution steps are:
·Rinse the glassware before use to remove impurities as the impurities may affect the result.
·Take the reading of solution with the eye is perpendicular to the meniscus to avoid parallax error.
· Use consistent rate of agitation for each mixture.
· Make sure the temperature was not exceed or less than stated temperature.
Conclusion
The solubility limits in a ternary system of water and two other liquids (ethanol and toluene) cannot be exactly obtained due to incomplete binomial curve.
References
1.http://www.lboro.ac.uk/research/phys-geog/tri-plot/
2. Website : "Ternary Phase Diagram" (http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/experimental/ternary2.html)
4. Martin's Physical Pharmacy and Pharmaceutical Science, Sixth Edition, Patrick J. Sinko, Wolters Kluwer, Lippincott Williams & Wilkins.
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