Aim/Objective
1.
To understand the system containing two
components by using curve.
2.
To determine the upper critical solution
temperature shown by the system containing water and phenol.
Introduction
The
mutual solubility of water and phenol is observed throughout this experiment.
When both liquids are heated, results obtained can be explained in the curve.
Area inside the curve shows the region where phenol and water mixtures will
form two separate layers. The region outside the curve indicates that phenol
and water exist in homogeneous solution, where no two separate layers can be
seen. Phenol is dissolved in water at different temperature. Both liquids
become soluble as the temperature increases until the critical solution
temperature is reached. The critical solution temperature here is defined as
the maximum temperature at where phenol and water can show two separate layers.
Both phenol and water become completely miscible in all proportions at a point
called upper critical solution temperature.
The
relative masses of two layers are explained by the lever rule as :
Materials
1. Phenol
2. Water
Apparatus
Beakers, tubes,
thermometer, electrical heater.
Procedures
1. The
tightly sealed tubes containing amounts of phenol and water were been done to
produce a phenol concentration scale between 8% to 80%.
2. The
tubes were heated in a beaker containing water to increase the temperature.
3. The
water was stirred and shaken as well.
4. The
temperature for each of the tube was observed and recorded at which the turbid
liquid becomes clear.
5. The
test tubes were removed from the hot water and were allowed for the temperature
to reduce gradually.
6. The
temperature was recorded at which the liquid becomes turbid and two layers are
separated.
7. The
average temperature was determined for each tube at which two phases are no
longer seen or at which two phases exist.
8. The
graphs of phenol composition in the different mixtures against temperature at
complete miscibility were plotted.
9. The
critical solution temperatures were determined.
Results
Percentage of Phenol (%)
|
Temperature (0C)
|
Average Temperature (0C)
|
|
Heating
|
Cooling
|
||
8
|
57
|
37
|
47
|
11
|
63
|
46
|
55
|
20
|
70
|
60
|
65
|
50
|
82
|
56
|
69
|
63
|
67
|
48
|
58
|
70
|
62
|
46
|
54
|
80
|
58
|
42
|
50
|
Graph shown above is plotted based on the results obtained in this experiment.
Temperature-composition diagram for the system consisting of water and phenol.
Discussions
Based on the graph
above, temperature fixed at 50 0C. At Point a, system containing
100% pure water. Addition of known increments of phenol to a fixed weight of
water will result in the formation of a single liquid phase until the point b
is reached. Point b, appears a second phase. The concentration is 11 % by
weight of phenol in water. Analysis of the second phase, which separates out on
top, shows it to contain 63 % by weight of phenol in water. easing quantities
of phenol, for instance, as we proceed across the diagram from point b to point
c, systems in which the amount of the phenol-rich phase (B) continually
increases at the same time the amount of the water-rich phase (A) decreases.
Once the total concentration of phenol exceeds 63 % at 500C a single
phenol-rich liquid phase is formed.
Tie line is always
parallel to the base line in two component systems. All systems prepared on a
tie line at 50° C will separate into phases of constant composition whose
composition is b and c. These phases are termed conjugate phases. All
combinations of phenol and water above this temperature are completely miscible
and yield one- phase liquid systems.
Even small
concentrations of salts may have large affects on phase separation and the
critical temperature. In aqueous solutions of organic molecules or polymers,
salt may be added to make the organic material form a phase separate from the
salty aqueous phase. This procedure may be familiar as "salting out."
The miscibility of phenol and water is reduced by addition of many common salts
such as alkali and alkaline-earth halides.2,3 The origin of the effect is the
tendency of water molecules to associate with ions, hydrating them. In that
way, simple ions reduce the tendency of water to solvate phenol. The result of adding
salt is often an increased critical temperature and greater phenol on the
phenol-rich side of the coexistence curve.
Conclusion
The critical solution temperature (upper consolute temperature) is the maximum temperature at which two phase region exists. In the case of the phenol-water system, this is 66.8° Celsius.
References
1. Textbook of Physical Chemistry, A. S. Negi, S. C. Anand, Page : 372-373
2. Patrick
J. S, Martin’s Physical Pharmacy and Pharmaceutical Sciences, 50th
Edition, 2011, Lippincott Williams & Wilkins
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