TITLE
Part A: DETERMINATION OF PHASE DIAGRAM FOR ETHANOL /
TUOLENE / WATER SYSTEM THEORY THREE-COMPONENT SYSTEMS
AIM
The aims of this lab are:
1.
To determine the solubility limits in a
three component systems of water with ethanol and ethanol in which ethanol is
completely miscible whereas toluene which is partly miscible in water.
2.
To construct the solubility curve of the
system on triangular diagram.
DATE
OF EXPERIMENT
2th November 2015
INTRODUCTION
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. Phase
diagrams are graphical
representations of the liquid, vapour, and solid phases that co-exist at
various ranges of temperature and pressure within a reservoir. Ternary phase
diagrams are 3 component systems and represent the phase behaviour of mixtures
containing three components in a triangular diagram. The three
components are usually compositions of elements, but may include temperature or
pressure also. It is necessary to know the three binary systems for the
three components to construct a ternary phase diagram. Ternary diagrams have a
vertical temperature axis.
Figure 1 :
Ternary Phase Diagram
In Figure 1, the
concentration of each pure component is 100% at each corner of the triangle and
0% at the line opposite it, which is 100% or A, 100% of B and 100% of C. Each
side represents two-component mixtures and within the triangular diagram itself
represents ternary components. By drawing line parallel to a side of the
triangular diagram shows constant percentage value for a component, for
example: DE shows 20% of A component with varying amounts of B and C. So does
line FG which shows all mixture containing 50% of B. These lines intercept with
each other at K, which contains 20% of A, 50% of B and 30% of C. Measurements
can be made this way because in a triangular diagram, the sum of all distances
from K which is drawn parallel to the three sides of the diagram is same and
equals to length of any side of the diagram.
The addition of a third component to
a pair of miscible liquids can change their mutual solubility and settle into 2
phases. If this third component is more soluble in one of the two different
components the mutual solubility of the liquid pair is decreased. However, if
it is soluble in both of the liquids, the mutual solubility is increased. For example when ethanol is added to a
mixture of benzene and water, the mutual solubility of the liquid pair
increased until it reached a point whereby the mixture becomes homogenous. This
approach is used in the formulation of solutions.
In pharmaceutical formulation,
multiple components need to be mixed together and be in homogeneous form. This
can be achieved by knowing the exact ratio of each component to be mixed with
regard of some other condition such as temperature. Examples of three-component
systems that has been studied include castor oil/ alcohol/ water; peppermint
oil/ propylene glycol/ water; peppermint oil/ polyethylene glycol/ water.
LIST OF MATERIALS
Toluene, ethanol, distilled
water
LIST OF APPARATUS
100cm3 conical
flask, burette, retort stand, measuring cylinder, test tubes
EXPERIMENTAL
PROCEDURES
1.
Ethanol/
toluene mixtures of different compositions were prepared and placed in sealed conical
flasks.
2. Eight 20 ml solution of toluene and ethanol were prepared in eight
different 100cm3 conical flasks.
3. Each flash were filled so that it
contain 10%, 25%, 35%, 50%, 65%, 75%, 90% and 95% of ethanol with the rest was
toluene.
4. The conical
flask were labelled A, B, C, D, E, F, G and H respectively.
5.
A
burette was filled with distilled water.
6.
The mixtures were titrated with water, accompanied by vigorous shaking of the
conical flask.
7.
Titration was stopped when a cloudy mixture was formed.
8.
The volume of the water used was recorded.
9.
Steps 1-6 were repeated to do a second titration. The volume of water required
for complete titration of each mixture was recorded.
10. Average
volume of water used was calculated.
11. %
volume of each component of the ternary system for when a second phase became
separated was calculated.
12. These
values were plotted on a graph paper with triangular axes to produce a triple
phase diagram.
RESULTS
Table
of data:
Conical flask
|
Component
|
Percentage (%)
|
Volume (mL)
|
A
|
Ethanol
|
14.71
|
2
|
Toluene
|
82.38
|
8
|
|
Water
|
2.91
|
12
|
|
B
|
Ethanol
|
21.74
|
5
|
Toluene
|
72.82
|
15
|
|
Water
|
5.44
|
10
|
|
C
|
Ethanol
|
31.13
|
7
|
Toluene
|
61.47
|
13
|
|
Water
|
7.40
|
3.5
|
|
D
|
Ethanol
|
45.23
|
7
|
Toluene
|
46.30
|
13
|
|
Water
|
8.47
|
1.6
|
|
E
|
Ethanol
|
57.49
|
10
|
Toluene
|
30.91
|
10
|
|
Water
|
11.60
|
1.9
|
|
F
|
Ethanol
|
61.48
|
13
|
Toluene
|
20.49
|
7
|
|
Water
|
18.03
|
3.2
|
|
G
|
Ethanol
|
59.31
|
18
|
Toluene
|
6.59
|
2
|
|
Water
|
34.10
|
10.3
|
|
H
|
Ethanol
|
51.35
|
19
|
Toluene
|
2.70
|
1
|
|
Water
|
45.95
|
16.2
|
QUESTIONS
1.) Does the mixture containing
70% ethanol, 20% water and toluene appear clear or does it form two layer?
The
solution appear clear.
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
Phase
diagrams are graphical representations of the liquid, vapor, and solid phases
that co-exist at various ranges of temperature and pressure within a reservoir.
Ternary phase diagrams represent the phase behavior of mixtures containing
three components in a triangular diagram. In this experiment, the mixtures of
ethanol and toluene in sealed containers containing following percentages of
ethanol (%) which are 10,25,35,50,65,75,90 and 95. Each mixture is titrated
with water until cloudiness is observed. This is due to the existence of second
phase.
There
are three apex in the ternary phase diagram above. Each of them represents 100%
by volume of one component which is water, ethanol and toluene. The side of the triangle,
directly opposite the apex, represents 0% of the apex component. The area within
the triangle represents all the possible combinations of ethanol, toluene and
water to give 3 components systems. Toluene and ethanol are miscible liquids.
Toluene is water insoluble liquid while ethanol completely react with water as
ethanol has OH- group. Water is a polar substance that will attract
OH- group. Hence water and ethanol will be miscible in any amount.
Due to the decrease in solubility of the three components mixture, two phases
diagram appears.
However,
based on the phase diagram plotted above, it is not accurate enough as we have
done some errors during the experiment. Firstly, during titration, the eye is
not perpendicular to the scale of the burette when taking the reading. The eye
must be perpendicular to the reading scale to avoid parallax error and obtain a
more accurate result. Besides, titration is not carried out in a proper way. We
should do the titration with drop by drop method so that we can stop the
titration process immediately at the first presence of two phases. Furthermore,
the tendency of cloudiness of all mixtures are not the same. Some may be less
and some may be more. The titration should be conducted by the same person
throughout this experiment to reduce the difference in the tendency of
cloudiness as this may affect the volume of water added to the solution and
eventually reduce the accuracy of the result.
Besides,
room temperature in the laboratory during the experiment was not kept constant.
It is one of the factor that will change the graph pattern. Lastly, ethanol and
toluene should be closed in a container and not exposed to the surrounding too
long time. This is because both ethanol and toluene are volatile liquids and
they may evaporate rapidly.
CONCLUSION
From
the experiment, the 3-component system is considered as condensed system. We
need to fix only 2 number of degree of freedom, which are temperature and pressure.
REFERENCE
http://petrowiki.org/Ternary_phase_diagrams
Sinko, P. J. (n.d.). Martin's Physical
Pharmacy and Pharmaceutical Science. Lippincott Williams & Wilkins.
No comments:
Post a Comment