TITLE:
Determination of Phase Diagram for Ethanol/Toluene/Water System Theory
Three-Component Systems
AIM:
1) To determine the solubility limit in ternary system of water and two
other liquids (ethanol & 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, multiple
substances need to be mixed together to form homogenous solution. Homogenous
solution can be formed by knowing the exact ration of each component to be
mixed with concern of other conditions like temperature and pressure. In this
particular experiment, three components involved are ethanol, toluene and
water. Water and toluene mixture is insoluble. When the mixture is added with
ethanol, all these three components can become a homogenous solution at
equilibrium if proper proportions are used.
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 composition of the points lie inside the area of triangle
can determined by using triangle grid method. Triangle 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 intersection 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.
EXPERIMENTAL METHOD:
MATERIAL AND APPARATUS:
Retort stand with clamp, conical flasks, burette, measuring cylinder,
toluene, ethanol, distilled water
PROCEDURES:
1) Mixture of ethanol and toluene was prepared in conical flasks
containging the following percentage of
ethanol( 10,25,35,50,65,77,90,95).
2) 20 ml of each mixture was prepared accurately by filling a certain
volume using a burette.
3) Each mixture was titrated using distilled water until cloudiness
appears due to the existence of a second phase.
4) Conical flasks were shaken well after addition of a little water.
5) The volume of water added into the mixture was recorded.
6) Few measurements were taken to get accurate readings.
7) The room temperature was
measured.
8) The percentage based on the volume of each component when the
second phase starts to appear was calculated.
9) Points were plotted in the triangular paper to obtain the triple
phase diagram at the recorded temperature.
RESULTS:
Conical Flask
|
Component of analyte
|
Volume of water used,
mL
|
|||
Ethanol
|
Toluene
|
||||
%
|
mL
|
%
|
mL
|
||
A
|
10
|
2.00
|
90
|
18.00
|
0.40
|
B
|
25
|
5.00
|
75
|
15.00
|
0.80
|
C
|
35
|
7.00
|
65
|
13.00
|
1.10
|
D
|
45
|
9.00
|
55
|
11.00
|
1.20
|
E
|
65
|
13.00
|
35
|
7.00
|
2.80
|
F
|
75
|
15.00
|
25
|
5.00
|
4.60
|
G
|
90
|
18.00
|
10
|
2.00
|
11.00
|
H
|
95
|
19.00
|
5
|
1.00
|
17.10
|
Percentage of the components after titration:
Conical
Flask
|
Percentage
of each Component of titration product
|
||
Ethanol(%)
|
Toluene(%)
|
Water(%)
|
|
A
|
9.80
|
88.24
|
1.96
|
B
|
24.04
|
72.16
|
3.85
|
C
|
33.18
|
61.61
|
5.21
|
D
|
42.45
|
51.89
|
5.66
|
E
|
57.02
|
30.70
|
12.28
|
F
|
60.98
|
20.33
|
18.70
|
G
|
58.06
|
6.45
|
35.48
|
H
|
51.21
|
2.70
|
46.09
|
The percentage of the components was calculated
using the formula:
Percentage = Volume of the component ÷ total volume
x 100%
PRACTICE:
1) Does the mixture containing
70% ethanol, 20% water and 10% toluene (volume) appear clear or does it form
two layers?
The
mixture remains clear and no cloudy solution appeared forming one homogenous
liquid phase.
2) 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= 1x 20/100= 0.2 part of water
1
part mixture x 10% toluene = 1x 10/100= 0.1 part of toluene
So,
in the mixture, there are 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%
Hence, based on
the phase diagram, this mixture is under the area of the binomial curve, so 2
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%
Hence, based on
the phase diagram, this mixture is outside the area of the binomial curve, so 1
phase 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%
Hence, based on the
phase diagram, this mixture is outside the area of the binomial curve, so 1
phase is formed.
DISCUSSION:
A phase diagram shows the phases
existing in equilibrium at any given condition. According to the Phase Rule, a
maximum of four intensive variables (intensive properties) must be specified to
completely define the state of a three-component system. The intensive
variables that are usually chosen are pressure, temperature and
concentration. According to the phase rule, a single phase in a
three-component system may possess four degrees of freedom. The calculation
involved is shown below:
F = C – P + 2 =
3 – 1 + 2 = 4
in
which F is degree of freedom; C is component; P is phase.
The addition of a third component to a
pair of miscible liquids can change their mutual solubility. If this third
component is more soluble in one of the two different components, the mutual
solubility of the liquid pairs is decreased. However, if it is soluble in both
of the liquids, the mutual solubility is increased. Thus, when ethanol is added
to a mixture of toluene and water, the mutual solubility of the liquid pair
increased until it reached a point whereby mixture become homogenous.
Regions where one or two phases appear
have been indicated in phase diagram for three-component system. When the three
components are mixed to give an overall system composition that falls in the
two phase region, the system will separate into two phases: a phase rich in
water and another rich in toluene. The curve of the plotted graph is termed as
binomial curve. The region bounded by the curve shows the presence of two
phases. The mixture within this region is cloudy in appearance due to phase
separation as the amount of ethanol is not sufficient for a homogenous mixture
to be produced. The region above the curve boundary shows one phase of
homogenous solution. Addition of ethanol which acts as surfactant allows the
two phase solution to be in one phase.
Based on the results obtained, when
there is a higher percentage of ethanol compared to the percentage of toluene
in the mixture, the volume of water needed to titrate the mixture until
cloudiness is observed is higher. This proves that the ethanol has increased
the miscibility of the other two components and more water is needed to break
the homogeneity. A second phase will only be separated out when the proportion
of water added exceed the theoretical percentage where three components are
partially miscible.
There is no fixed indication. The
appearance of cloudiness in the solution exists in variety of its intensity. So,
it is hard to determine the most accurate volume of titrant that is correlated
with the appearance of cloudiness that comes with different intensity.
The apparatus should be rinsed with the
distilled water to avoid any external reaction. One of the precautions is the
same person should observe all the cloudiness of mixture every time throughout
the experiment. The observer should make sure the eyes are perpendicular to the
lower meniscus of the liquids to avoid parallax error. The volatile liquids
should be poured immediately from the container to the conical flasks to
minimize loss of volume. The room temperature must be consistent. The apparatus
must be clean and dry to avoid contamination. The mixture should be well
agitated then allowed to attain equilibrium.
CONCLUSION:
The
reaction of water, toluene and ethanol appears as two phase system due to the
decreasing in solubility of the mixture.
REFERENCE:
1)
http://www.chm.davidson.edu/vce/phasechanges/PhaseDiagram.html
2)
http://www.csun.edu/~jeloranta/CHEM355L/experiment5.pdf
3)
Martin's Physical Pharmacy and Pharmaceutical Science, Sixth Edition, Patrick
J. Sinko, Wolters Kluwer, Lippincott
Williams & Wilkins.
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