PART A
Title
: Determination of
Phase Diagram for Ethanol/Toluene/Water System Theory
Objectives
1. To
understand the concept of phase diagram.
2. To
determine the phase diagram for ethanol, toluene and water system theory.
Date of experiment : 4 November 2014
Introduction
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 represent the phase behaviour of mixtures containing
three components in a triangular diagram, hence it is also known as three
component systems. For three component systems at constant temperature and
pressure, the compositions may be stated in the form of coordinates for a
triangular diagram.
In the diagram, each corner of the
triangular diagram represents a pure component A, B and C respectively which
all are 100 per cent pure. Meanwhile, each side of the triangle represents
two-component mixtures and within the triangular diagram itself represents
ternary components. Any line parallel to a side of the triangular diagram shows
constant percentage value for a component, for instance, line DE shows 20% of A
with varying amounts of B and C, line FG, showing all mixtures containing 50%
of B. The interception point, K contains 20% A, 50% B as well as 30% 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 the length of any one side of the triangular diagram.
The mutual solubility of two miscible
liquids can be altered when a third component is added into them. If this third
component is more soluble in one of the two different components the mutual
solubility of the liquid pair is decreased. On the other hand, if it is soluble
in both of the liquids, the mutual solubility is increased. 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. Examples of three-component systems that have been studied
include castor oil, alcohol, water; peppermint oil, propylene glycol, water;
peppermint oil, polyethylene glycol, water.
In
this system, there are 3 components but only 1 phase exists. Thus, by using the
phase rule, it is determine that this system have 4 degrees of freedom which
are temperature, pressure, and any two from the three component concentration.
Calculation for degree of freedom:
F = C – P + 2
F = 3 – 1 + 2
F = 4
Material and Apparatus
 |
| Burette and Retort Stand |
 |
| Toluene |
 |
| Sulphuric Acid |
 |
| Distilled Water |
 |
| Measuring Cylinder |
 |
100 cm3 Conical Flask
|
Experimental
Procedures
1. Mixtures
of ethanol and toluene are prepared in sealed containers measuring 100cm3
containing the following percentages as well as volume of ethanol and toluene.
Container
|
Ethanol
|
Toluene
|
Percentage (%)
|
Volume (ml)
|
Percentage (%)
|
Volume (ml)
|
A
|
10
|
2
|
90
|
18
|
B
|
25
|
5
|
75
|
15
|
C
|
35
|
7
|
65
|
13
|
D
|
50
|
10
|
50
|
10
|
E
|
65
|
13
|
35
|
7
|
F
|
75
|
15
|
25
|
5
|
G
|
90
|
18
|
10
|
2
|
H
|
95
|
19
|
5
|
1
|
2. Each
mixture is titrated with water until cloudiness is observed due to the
existence of a second phase by using a burette.
3. A
little water is added and shaken well after each addition.
4. The
room temperature is measured.
5. The
percentage is calculated based on the volume of each component when the second
phase starts to appear.
6. The
points are plot onto a triangular paper to give a triple phase diagram at the
recorded temperature.
Result
Containers
|
Volume
of water added (ml)
|
A
|
0.0
|
B
|
0.2
|
C
|
1.2
|
D
|
1.6
|
E
|
2.7
|
F
|
4.2
|
G
|
10.4
|
H
|
16.1
|
Containers
|
Percentages
(%)
|
Ethanol
|
Toluene
|
Water
|
A
|
10.00
|
90.00
|
0.00
|
B
|
24.75
|
74.26
|
0.99
|
C
|
33.02
|
61.32
|
5.66
|
D
|
46.30
|
46.30
|
7.40
|
E
|
57.27
|
30.84
|
11.89
|
F
|
61.98
|
20.66
|
17.36
|
G
|
59.21
|
6.58
|
34.21
|
H
|
52.63
|
2.77
|
44.60
|
Discussion
In ternary phase diagrams, the
solubility of two liquid can be changed when a third component is added. There
are two possible outcomes. First, if the third component is soluble in both the
liquid, it may increase the solubility of the system. Hence, it can be used to
mix two immiscible or slightly immiscible components such as water and benzene.
Initially, water and benzene appear in two phase but once alcohol is added into
the system, the final solution contains only one phase. Secondly, the other
possible outcome is if the third component added is only soluble in one of the
two different components, the solubility of the system will be decreased.
In this experiment, we used ethanol,
toluene, and water. Water is used as the third component. As we know, toluene
is soluble in alcohol; hence toluene is miscible in ethanol. On the other hand,
toluene is insoluble in water while ethanol is soluble in water. As a result,
the solubility of the system will decrease as water added into the mixture of
toluene and ethanol. Cloudiness which indicates the existence of two phases is
observed in the end of the experiment.
In the triangular paper, the top corner
of the triangle is labelled as toluene, the left corner is ethanol while the
right corner is water. Each corner represents 100% pure of the three components
respectively. Any points on the sides of the triangle show that there are only
two components while the points within the triangle show that there are three
components in the mixtures.
Based on the triangular paper, a curve
can be drawn when all the points on the paper are joined together. The curve
separated the triangular paper into two sides, left and right. On the left side
of the curve, the mixtures appear to have only one phase. Meanwhile, on the
right side of the curve, the mixtures appear to have two phases and cloudiness
can be observed.
There are several errors that were formed when conducting
this experiment which leads to this inaccuracy .They includes:
- Exact point when to stop water
titration is determined wrongly as the
cloudiness disappearance was not observed properly.
- The eye level of the observer
was not perpendicular to the reading scales
- Different rate of agitation may
influence the disappearance of cloudiness.
- The apparatus used were not
clean completely before the experiment was started.
- The temperature during the
experiment is not consistent.
To improve the accuracy of the
result of experiment, some precautions must be taken. They include:
- The eye level of the observer must be perpendicular to the
reading skills to avoid parallax errors.
- Use consistent rate of agitation for each mixture.
- Clean the apparatus before using it. This is to ensure that
the apparatus is free contamination.
- The temperature of surrounding must be fixed.
- Mask and gloves must be worn throughout the experiment as a
protection from dangerous chemical.
Questions
1. Does
the mixture containing 70% ethanol, 20% water and 10% toluene (volume) appear
clear or does it form two layers?
The mixture will appear
clear. Based on the triangular paper, the point is plotted on the left side of
the curve therefore a clear solution can be observed.
2. What will happen if you dilute 1 part of the
mixture with 4 parts of (a) water (b) toluene (c) ethanol?
(a) Water:
Two phases
will be observed.
(b) Toluene:
Two phases
will be observed.
(c) Ethanol:
One phase
will be observed, the solution remain clear.
Conclusion
Ethanol,
toluene and water system is a ternary system with one pair of partially
miscible liquid (toluene and water). The addition of sufficient amount of
ethanol to the toluene-water system would produce a single liquid phase in
which all the three components are miscible and the mixture is homogenous. The
phase diagram for Ternary System is determined.
Reference
1.)
http://www.chm.davidson.edu/vce/phasechanges/PhaseDiagram.html
4.)http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Phases_of_Matter/Phase_Transitions/Phase_Diagrams
5.)
Physicochemical Principles of Pharmacy, 3rd edition (1998) . A.T. Florence and
D.Attwood. Macmillan Press Ltd.
6.)
Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences, by
Martin, A.N.
