PRACTICAL 3:PHASE DIAGRAM
PART B
TITLE:
Mutual solubility curve for phenol and water
DATE OF EXPERIMENT:
3rd November 2014
OBJECTIVES:
To measure the miscibility temperatures of several water-phenol mixtures of known composition
To
construct and understand the
To
determine upper consolute/critical temperature of water-phenol mixtures
INTRODUCTION:
A phenol – water solution was used to determine the solubility of two
partially miscible liquids. The group
calculated the volume of water required to prepare the following mixtures with
volume percentage ranging from 5% to 95% sample at 5% increment using 10mL
phenol sample. The different volume
ratios of mixtures prepared were subjected to constant heating and cooling in
order to gather the needed temperature necessary for the construction of the
mutual solubility curve of Phenol- Water solution.
Mutual solubility of the components in a liquid-liquid system may
results complete miscibility or partial miscibility. Complete miscibility can
be defined as particles involves are well distributed or fully mixed (mix in
all proportions; “like dissolve like”). Meanwhile, partial miscibility is the
formation of two layers when certain amounts of liquids are mixed. Two
liquids are “partially miscible” if shaking equal volumes of the liquids
together results in a meniscus visible between two layers of liquid, but the
volumes of the layers are not identical to the volumes of the liquids
originally mixed.
In the experiment, we used water and phenol to discuss the idea of this mutual
solubility. Phenol-water binary system is a system that shows the nature of the
mutual solubility between phenol and water at a certain temperature and fixed
pressure. According to the theory, water and phenol have the property of
partial miscibility when it is initially mixed. As we learnt, mutual solubility of
partially miscible mixture is influenced by temperature.
As the temperature of
the water-phenol mixture is increased, it will reach a critical point or we
called it as upper consolute temperature where the homogenous mixture will
form. Thus, under or beyond this critical point temperature, it will become
heterogeneous or 2 layers of mixture will form back. In this phase, the
compositions for two liquid phases in equilibrium are constant and are not
affected by the relative amount of these two phases. These phases are termed
conjugate phases. The relative amounts of the two phases vary. The miscibility
between two partial miscible liquids is normally affected by the existence of
third component. For more understanding of this mutual solubility of
phenol-water mixture, the plot of mutual
solubility curve for phenol and water(temperature measured versus phenol
composition) is needed. By doing so, we can easily know the critical point
temperature, temperature for each phenol composition for the mixture to change
to the phase required and many more.
APPARATUS:
Thermometer
Test tubes
Parafilm
Test tube holder
Water bath
MATERIALS:
Phenol,Water
EXPERIMENTAL PROCEDURES:
1) Students were given tightly sealed tubes
containing amounts of phenol concentration scaled between 8% to 80%.
2) In order to increase the temperature through
heating, students were about to heat the tubes in the beaker containing water.
3) The water was stirred and
the tubes were shaken as well. The temperature for each of the tube at which
the turbid liquid becomes clear were observed and recorded.
4) The tubes were removed
from the hot water and the temperature was allowed to reduce gradually, the
temperature at which the liquid becomes turbid and two layers were separated.
5) The average temperature
for each tube at which two phases were no longer seen or at which two phases
exists were determined.
6) Part of the tubes was to
be cooled besides being heated as instructed above.
RESULTS:
Tabulation of data
PERCENTAGE OF PHENOL (%)
|
VOLUME OF PHENOL (mL)
|
VOLUME OF DISTILLED WATER (mL)
|
AVERAGE TEMPERATURE AT WHICH THE TURBID
LIQUID BECOMES CLEAR (°C)
|
AVERAGE TEMPERATURE AT WHICH THE LIQUID
BECOME TURBID (°C)
|
8
|
1.6
|
18.4
|
35
|
33
|
11
|
2.2
|
17.8
|
50
|
45
|
20
|
4.0
|
16.0
|
68
|
65
|
35
|
7.0
|
13.0
|
69
|
64
|
50
|
10.0
|
10.0
|
65
|
60
|
63
|
12.6
|
7.4
|
60
|
58
|
70
|
14.0
|
6.0
|
55
|
51
|
80
|
16.0
|
4.0
|
44
|
39
|
Graph
A
graph of Composition of Phenol in water (% by volume) against Temperature at complete
miscibility (°C )
Temperature at complete miscibility ( °C ) |
|
Composition of Phenol
in
water (% by volume)
DISCUSSION:
Phase rule is a useful and may be used to determine the variance of any system
at equilibrium. It is used to relate the effect of the least number of
independent variables like pressure, temperature and concentration upon the
various phases (solid, liquid and gaseous) that can exist in an equilibrium
system containing a given number of components. There are some factors to be
considered in order for the system to be in equilibrium. Those are the degree
of freedom (F), the number of component making up the phases (C) and the number
of phases that can coexist or the number of phases in thermodynamic equilibrium
with each other (P). The number of degrees of freedom is the number of
independent intensive variables.
The rule is the equality:
F = C – P + 2
In this
experiment, the phenol and water are partially miscible. We plotted the graph
of average temperature against percentage of phenol based on the data we
obtained in the experiment. We get an n-shaped graph after it is been plotted.
The peak of the graph showed the critical temperature for the solution where
critical solution temperature is the temperature at which a mixture of two
liquids (Phenol and Water for this experiment), immiscible at ordinary
temperatures, cease to separate into two distinct phases. The region outside
the curve will have one liquid phase and the region within the curve will have
two liquid phases. The first boiling tube containing 8 % of phenol and the last
boiling tube containing 80% will have their mixtures exist as one liquid phase.
As the percentage of phenol increases, the amount of phenol-rich phase will
continuously increase and forming two phases system. Finally, the critical
solution temperature for this experiment is 69 °C. In this experiment, we are
measuring the temperature of the phenol-water system at miscible and
temperature at which two phases separated.
There are some
precautionary steps that should be taken during this experiment. Firstly, after
inserting the thermometer into the test tube, the tube must be sealed
immediately and tightly to prevent evaporation of phenol once it is mixed with water.
This is to ensure the accuracy of the result obtained as evaporation of phenol
may affect the result. Besides, this step also ensures that there will be no
heat lost to the surrounding when the test tube is heated in water bath and
when the temperature is measured. Parallax error also may occur when we measure
the volume of phenol and water and recording of the temperature of the
thermometer. The desired volume of phenol may not be obtained due to this error
and thus causes deviation the result of the experiment. Lastly, we must be very
careful in taking the reading of the temperature when heating and cooling the
mixtures. This is to avoid the inaccuracy in the result of the experiment as
the temperature will increase or decrease rapidly.
CONCLUSION:
The critical solution
temperature peaks at 69°C. A two-component system is formed between phenol and
water. In this experiment, both water and phenol are partially miscible.
QUESTIONS
QUESTIONS
Explain
the effect of adding foreign substances and show the importance of this effect
in pharmacy.
The
foreign substances will affect the critical solution temperature. If the
foreign substance is soluble in one of the two liquids, the mutual solubility
of the latter is destroyed, and the temperature at which the system becomes
homogeneous is raised.This increase in temperature is due to the salting out of
water. When the added substance dissolves in both the liquids, the critical
solution temperature is lowered due to negative salting out effect. This effect
is important to the industrial production of highly concentrated solutions of
tar acids (phenols and cresols) used as disinfectants.
REFERENCE:
3 3) http://www.scribd.com/doc/116082090/The-Binary-System-Phenol
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