TITLE: Determination of phase diagram for
ethanol/toluene/water system.
AIM: To
determine the phase diagram for ethanol/toluene/water system.
APPARATUS: retort stand and clamp,
burette, pipette, conical flask,measuring cylinder
 |
| dropper |
 |
| conical flask |
 |
| measuring cylinder |
CHEMICALS:
ethanol, toluene, distilled water.
 |
| ethanol |
 |
| toluene |
INTRODUCTION:
A phase diagram is
a graph that shows under what conditions distinct phases of matter occur and it
is to elaborate about a phase or state. The major features of a phase diagram
is the triple point and phase boundaries. The phase rule is a device to relate
the effect of the least number of independent variables upon the various phases
that can exist in an equilibrium system containing given number of components.
Phase rule is expressed as:
F=C
– P + 2
F=number
of degrees of freedom
C=number
of components
P=number
of phases
Based on the figure
above, each point A, B and C each represents pure components in 100%. Each side
of the triangle represents the two-component mixtures and within the triangle,
it represents the ternary components. Furthermore, any lines that is parallel to
the side of the triangle is a percentage value for the component. At point K,
the line intercepts that shows it has 20% A, 50% of B and 30% of C. The sum of
all distances from K is of the line that is drawn parallel to the sides of the
triangle is same and equals to the length of any side of the triangle.
An addition of a third component to a pair of miscible
liquids can change the two components’ mutual solubility. If the third
component is soluble in one of the tow components, the mutual solubility of the
liquid pair is decreased. Nevertheless, if the third component is soluble in
both of the liquids, the mutual solubility is increased. In an example of
mixture of benzene and water, when ethanol is added, the mutual solubility of
the liquid pair increased until it reaches a point where the mixture becomes
homogenous since ethanol is miscible in both benzene and water. This method had
been used in the formulation of solutions between castor oil, alcohol and water
including between peppermint oil propylene glycol and water.
There are many benefits of preparing an oily substance as
homogenous water in liquid. The understanding of the triangular phase diagram
can help explain what will happen to the system when it is diluted.
PROCEDURES:
PROCEDURES:
- Mixtures of ethanol and toluene are prepared in sealed containers measuring 100cm3 which according to percentages of ethanol (in percent: 10, 25, 35, 50, 65, 75, 90, 95)
- 20ml of each mixture are prepared by filling a certain volume using a burette.
-
Each
mixture is filtrated with distilled water until cloudiness is observed which
indicates the existence of second phase.
cloudiness appeared after the addition of distilled water -
A
little of water is added and then shaken well after the addition into mixtures.
- The room temperature is measured.
- The percentages are calculated based on the volume of the each component when the second phase starts to appear.
- The points are plotted onto triangular paper to give a triple phase diagram at the recorded temperature.
- Each determination in this experiment is repeated again to obtain an accurate result.
| RESULTS: | ||||||||||||||||
|
Test Tube
|
Ethanol in
|
Ethanol
|
Toluene
|
Distilled water
|
Total Volume
|
|||||||||||
|
percentage
|
Volume of
|
% of ethanol
|
Volume of
|
% of toluene
|
Average of
|
% of water
|
(ml)
|
|||||||||
|
(%)
|
ethanol(ml)
|
after titration
|
toluene(ml)
|
after titration
|
water added
|
added
|
||||||||||
|
A
|
10
|
2
|
9.3
|
18
|
83.9
|
1.45
|
6.8
|
21.45
|
||||||||
|
B
|
25
|
5
|
22.8
|
15
|
68.5
|
1.9
|
8.7
|
21.90
|
||||||||
|
C
|
35
|
7
|
33.4
|
13
|
62.1
|
0.95
|
4.5
|
20.95
|
||||||||
|
D
|
50
|
10
|
46.1
|
10
|
46.1
|
1.7
|
7.8
|
21.70
|
||||||||
|
E
|
65
|
13
|
58.0
|
7
|
31.3
|
2.4
|
10.7
|
22.40
|
||||||||
|
F
|
75
|
15
|
60.9
|
5
|
20.3
|
4.7
|
18.9
|
24.70
|
||||||||
|
G
|
90
|
18
|
60.6
|
2
|
6.7
|
9.7
|
32.7
|
29.70
|
||||||||
|
H
|
95
|
19
|
52.9
|
1
|
2.8
|
15.9
|
44.3
|
35.90
|
||||||||
 |
| the triangular phase diagram of ethanol/water/toluene |
DISCUSSION:
The
experiment is conducted to determine the phase diagram of ethanol/toluene/water
system. Toluene is miscible in ethanol but immiscible in water. But all these
three component can be miscible if mixed until certain portion. This experiment
is carried out by first mixing the ethanol and toluene which is completely
miscible in a conical flask. Then water is titrated into the mixture which is
at first will formed in two phase but, as we continue add water into the
mixture until reach appropriate amount it will exist in one phase.
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 below the graph shows two phase
system, while the region above the graph shows homogenous mixture.
According to phase rule: P + F = C + 2, Where P is the number of phases in the system
C is the minimum number of chemical components required to constitute all the phases in the system F is the number of degrees of freedom in the system (also referred to as the variance of the’ system).
C is the minimum number of chemical components required to constitute all the phases in the system F is the number of degrees of freedom in the system (also referred to as the variance of the’ system).
For ethanol/toluene/water system, we have 3
components and 1 liquid phase. F= 3-1+2= 4. Hence, 4 degrees of freedom are
required. They are temperature, pressure, and the concentrations of two of the
three components. Only concentrations of two components are required because
concentration of the third component can be obtained by further calculation.
The experiment was carried out at a constant temperature and pressure. The
temperature when this experiment is carried out is 27°C.
Based on the result obtained, when the
percentage of ethanol is high and the percentage of toluene is low, more water
is needed to observe the cloudiness of the mixture. The cloudiness of the
mixture indicates the two phase system. This proved that the ethanol had increased the miscibility of the other
two components and more water is needed to break the homogeneity.
There are some errors occur during the
experiment is conducted. Firstly, the apparatus is not clean and dry. If the
apparatus is not dry, it may affect the result obtained as the water react with
mixture of toluene and ethanol. Next, parallax error which may occur when the
reading of the buret is taken. Finally, the titration is done by different person
so, the observation of the cloudiness might be different.
The precaution steps that must be taken are
make sure the apparatus is clean and dry before use it. Next, make sure the
level of eye is perpendicular to the reading scale of the apparatus in order to
avoid the parallax error. Finally, the titration process should be conducted by
one person only to make sure the observation of the cloudiness is the same for
all titration.
QUESTIONS:
1) Does the mixture containing 70%
ethanol, 20% water and 10% toluene (volume) appear clear or does it form two
layers?
The mixture of these solutions would appear as one
phase since ethanol is majority in percentage where ethanol can dissolve in
both water and toluene. As the result,
clear solution is obtained.
2) What will happen if you dilute 1 part
of the mixture with 4 parts of…?
a) Water
b) Toluene
c) Ethanol
a)
1 part of mixture with 4 parts of water.
Based
on the phase diagram, a clear solution is obtained since the percentage of
mixture is outside the bimodal ternary curve.
b)
1 part of mixture with 4 parts of toluene
A
cloudy solution would be obtained which mean that the solution appear have 2
phase since the percentage of the mixture is within the bimodal ternary curve.
c) 1 part of mixture and 4 parts of ethanol
Based
on the phase diagram, a single phase solution would be obtained since the
percentage of the mixture is located outside of bimodal ternary curve. A clear
solution is obtained.
CONCLUSION:
Water, toluene and
ethanol is ternary system and ethanol which acts as the other component added
to the liquid pair is soluble in both water and toluene. Toluene is immiscible
in water and as ethanol is miscible in both water and toluene thus it helps to
increase the mutual solubility between water and toluene. From the graph, the
area bounded shows a two-phase system and the area that are not bounded or
above the graph shows that a homogeneous mixture.
REFERENCE:
- Alfred.N Martin. 2006. Martin’s Physical Pharmacy and Pharmaceutical Sciences: Physical Chemical and Biopharmaceutical principles in the Pharmaceutical Sciences. Patrick J. Sinko, Yashveer Singh, David B. Troy. 6th Edition. Maryland: Lippincott William & Wilkins.
- Boundless. “Major Features of a Phase Diagram.” Boundless Chemistry Boundless, 26 May. 2016. Retrieved 12 Dec. 2016 from https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/liquids-and-solids-11/phase-diagrams-91/major-features-of-a-phase-diagram-395-1266/
