Practical 1 :
Phase Diagram
PART A
Determination of
Phase Diagram For Ethanol / Toluene / Water System Theory
Tree-Component System
OBJECTIVE:
To study the miscibility of ethanol / toluene / water system
and to investigate the behavior of system of the three liquid which is ethanol,
toluene and water.
APPARATUS:
Burette, conical flask, retort stand, measuring cylinder,
test tubes
MATERIALS:
Ethanol, Toluene, Water
INTRODUCTION:
Phase diagrams for ternary systems are usually represented using a
triangle shown in Fig. 2.
Figure 1
A
three-component phase diagram has four degrees of freedom: F = 3 − 1 + 2 = 4. In
this case, temperature and pressure are two of the conditions and the
concentrations of two of the three components make up the rest. In this
diagram, each of three corners or apexes of the triangle represent 100% by
weight of one component (in this experiment ethanol, toluene, water). As the
result the other two apex will represent 0% of the other two components.Only
two concentrations are required because the third will be the difference
between 100% and the sum of the other two components.
These
systems are used for determining miscibility/solubility, coacervation regions,
gel-forming regions for multicomponent mixtures, etc. The lines joining the
corner points forming the triangle each represent two component mixtures of the
three possible combinations (AB, BC, and CA). If two of the components are known,
the third is known by difference. Any combination of the three components is
described by a single point on the diagram. 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 pair is decreased.
However, if it is soluble in both of liquids the mutual solubility is
increased. Thus, 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 become homogenous.
PROCEDURES:
- Ethanol/ toluene mixtures of different compositions were prepared and placed in sealed conical flasks.
- Each mixture contained different % volume of ethanol in 50 ml: 10, 25, 35, 50, 65, 75, 90, 95% v/v.
- A burette was filled with distilled water.
- The mixtures were titrated with water, accompanied by vigorous shaking of the conical flask.
- Titration was stopped when a cloudy mixture was formed.
- The volume of the water used was recorded.
- Steps 1-6 were repeated to do a second titration. The volume of water required for complete titration of each mixture was recorded.
- Average volume of water used was calculated.
- % volume of each component of the ternary system for when a second phase became separated was calculated.
- These values were plotted on a graph paper with triangular axes to produce a triple phase diagram.
RESULTS:
Ethanol
|
Toluene
|
Water
|
||||
Volume of Ethanol /mL
|
% of Ethanol
|
Volume of Toluene/mL
|
% of Toluene
|
Volume of Water/mL
|
% of Water
|
|
2.0
|
9.9
|
18.0
|
88.7
|
0.3
|
1.5
|
|
5.0
|
24.0
|
15.0
|
72.1
|
0.8
|
3.9
|
|
7.0
|
33.3
|
13.0
|
61.8
|
1.1
|
5.0
|
|
10.0
|
45.6
|
10.0
|
45.6
|
2.0
|
8.9
|
|
13.0
|
55.6
|
7.0
|
30.0
|
3.4
|
14.5
|
|
15.0
|
60.0
|
5.0
|
20.0
|
5.0
|
20.0
|
|
18.0
|
59.0
|
2.0
|
6.6
|
10.6
|
34.5
|
|
19.0
|
49.0
|
1.0
|
2.6
|
18.8
|
48.5
|
|
QUESTIONS:
1.
Does
the mixture containing 70% ethanol, 20% water, and 10% toluene (volume) appear
clear or does it form two layers?
No. The solution appear clear and form one liquid phase.
2.
What
will happen if you dilute one part of the mixture with four part of (a) water
(b) toluene (c) ethanol?
The mixture contain 70% ethanol, 20% water and 10% toluene
1 part x
70/100 = 0.7 part of ethanol
1 part x
20/100 = 0.2 part of water
1 part x 10/100 = 0.1 part of toluene
~There are 0.7
part of ethanol, 0.2 part of water, 0.1 part of toluene in the mixture.
(a)
One part mixture + four part water
Ethanol = 0.7
--------- × 100%
1+4
=
14%
Water = 0.2 +
4
---------- × 100%
1+4
=
84%
Toluene = 0.1
----------× 100%
1+4
= 2%
̃ based on phase diagram, the mixture is outside the
curve. Thus single liquid phase will formed.
(b)
One part of mixture + four part toluene
Ethanol = 0.7
----------- × 100%
1+4
= 14%
Water = 0.2
---------- × 100%
1+4
= 4%
Toluene = 0.1 + 4
----------× 100%
1+4
=82%
̃ based on phase diagram, the mixture is outside the
curve. Thus, single liquid phase will formed.
(c)
One part mixture + four part ethanol
Ethanol = 0.7 + 4
----------- × 100%
1+4
= 94%
Water = 0.2
---------- × 100%
1+4
= 4%
Toluene = 0.1
----------× 100%
1+4
=2%
̃ based on phase diagram, the mixture is outside the curve.
Thus, single liquid phase will formed.
DISCUSSION:
For the diagram, each corner represent 100%
of each component, which is 100% toluene, 100% ethanol, and 100% water while
the other two component 0%. In going along the line bounding the triangle
represent the concentration in two-component system, it does not matter whether
we proceed in a clockwise or counterclockwise direction. But the more usual
convention is clockwise. In this case, as we move along water to ethanol in the
direction of ethanol, we assume the system of containing increasing
concentration of ethanol and smaller amounts of water. Moving along ethanol to
toluene will results in increasing amount of toluene and the closer we approach
water, the more its concentration will be. For example, at the first point the
amount of ethanol increases as we read it in clockwise. Ethanol is 9.9%, water
1.5% and toluene 88.7%. Result obtained in this experiment was not accurate due
to some error occurred during the experiment. Some of the error occurred are
parallax error during recorded and measured the scale. Furthermore, the
temperature also is not constant causing the measurement become slightly
deviated and some of the glassware have been contaminated causing the chemical
mixed with other compound. All this error causing result to be inaccurate and
slightly affect the graph obtained.
Some precaution need to be taken such as make
sure our eyes are parallel with the meniscus so that measurement is more accurate.
We also need to make sure the temperature is constant so that the reaction of
the chemical are almost the same for all set and clean the apparatus before use
to reduce contamination.
CONCLUSION:
Water and toluene form a two-phase
system because they are only slightly miscible. Ethanol is completely miscible
with both toluene and water. The rule that relate to the use of triangular
coordinates fully explained the three-component system.
REFERENCES:
3.
Martin’s Physical Pharmacy And Pharmaceutical
Sciences, 6th edition (2011). Patrick J. Sinko. Lippincott Williams
and Wilkins
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