Title:
Experiment 3 (Phase Diagram Part B) - Mutual Solubility Curve for Phenol and
Water.
Date
of experiment: 10th November 2016
Aim:
1.
To determine the solubility of two
partially liquids ( phenol- water solution)
Introduction:
A few liquids are
miscible with each other in all proportions, for example: ethanol and water.
Others have miscibility in limited proportions in other liquids, for example:
etherwater, phenol-water. The curve gbhi shows
the limits of the temperature and concentration within which two liquid phases
exist in equilibrium. The region outside the curve contains systems having but
one liquid phase.
Generally, both liquids
become more soluble more soluble with rising temperature until the critical
solution temperature or consulate point is attained and above this point the
liquids become completely miscible. There is a big possibility that any pair of
liquids can form a closed system, whereby both upper and lower critical
solution temperature exist, however it is not easy to determine both the
temperatures (before the substances freezes or evaporates).
At any temperature
below the critical solution temperature, the composition for the two layers of
liquids in equilibrium state is constant and does not depend on the relative
amount of these two phases. The mutual solubility for pair of partially
miscible liquids in general is extremely influenced by the presence of a third
component.
Apparatus/Materials:
Boiling tubes, Beaker,
Thermometer, Test tube holder, Parafilm, Measuring cylinder, Dropper
Chemicals:
Distilled water, Phenol
Procedure:
1. Prepare
5 boiling tubes with labels A, B, C, D and E
2. Tightly
seal the boiling tubes with water and different concentration of phenol – 8%,
30%, 50%, 70% and 80% respectively to the boiling tubes.
3. The
boiling tubes heated with water to increase the temperature of solution.
4. The
solution stirred and boiling tubes shake.
5. When
the turbid liquids become clear, the temperature of the boiling tubes observed
and recorded.
6. The
boiling tubes removed from the heated water and allowed the boiling tubes
reduce the temperature gradually.
7. The
temperature of boiling tubes when the liquid becomes turbid and two layers
separated is recorded.
8. Average
temperature for each tube at which two phases are no longer seen or at which
two phases exist is determined (Part of the tubes may need to be cooled besides
being heated as instructed above).
Results
Percentage of phenol %
|
Volume of phenol (mL)
|
Volume of water (mL)
|
Temperature (˚C)
|
Average temperature (˚C)
|
|
During heating
|
After heating
|
||||
8
|
1.60
|
18.40
|
77.00
|
31.00
|
54.00
|
30
|
6.00
|
14.00
|
80.00
|
51.00
|
65.50
|
50
|
10.00
|
10.00
|
51.00
|
41.00
|
46.00
|
70
|
14.00
|
6.00
|
79.00
|
32.00
|
55.50
|
80
|
16.00
|
4.00
|
60.00
|
30.00
|
45.00
|
Critical solution temperature of phenol-water system is 65.5 oC
Discussion
Phase rule is a useful device for relating effect of
the least number of independent variables such as temperature, pressure and
concentration upon the various phases (solid, liquid and gaseous) that can
exist in an equilibrium system containing a given number of components. The
phase rule can be expressed as F=C-P+2 where
·
F
= the number of degrees of freedom in the system
·
C
= the number of components
·
P
= the number of phase present
In this experiment, the phases of the two components
used which are phenol and water depend on the conditions the experiment was
conducted. When phenol and water and water are miscible at a particular
condition, having one-phase liquid system, the degree of freedom is, F=2-1+2
=3. Since this is a condensed system (the pressure of the system is fixed), F
is reduced to 2. This means that only two variables are needed which are
temperature and concentration to define the system. When phenol and water are
immiscible with each other, the degree of freedom is, F=2-2+2 =2. Since the pressure
is fixed for this system, F is reduced to 1. This means that temperature is the
only variable to define the system.
This
experiment is conducted to determine the solubility of two partially liquid
(phenol-water solution). Based on graph, the graph shows the temperature at
complete miscibility of the solution against the percentage of phenol
composition in the solution. The region inside the curve shows that the
solution has two phase system while the region inside the curve shows that the
solution is completely miscible and exist in one-phase liquid system. In this
experiment, the maximum temperature which are the critical solution temperature
of phenol-water system obtain is 65.5 oC. As the percentage of
phenol increases, the amount of phenol-rich phase increases and the amount of
the water-rich phase decreases. The theoretical critical solution temperature
for this phenol-water system is 66.8 oC.
From the result obtained, one of the point obtained is
slightly deviated from the graph and the critical solution temperature obtained
also slightly different from the theoretical value. This may due to some errors
that occurred during the experiment. Firstly, the parafilm is not sealed
properly on the boiling tube. This parafilm is used to prevent the escaping of
vapour from the boiling tube and to fixed the pressure for this experiment. If
the boiling tubes are not sealed properly, the heat will escape the surrounding
when the temperature is measured. To overcome this error, the parafilm should
be sealed properly on the boiling tube. Next, the reading of temperature is not
being recorded immediately after a particular condition is obtained. This might
affect the accuracy of the results. To overcome this result, the reading of
temperature should have been recorded immediately after a particular condition
is obtained. Lastly, parallax error occurred when taking the reading of
measuring cylinder to measure the volume of the two components (phenol and water)
and also when taking the reading of the thermometer. To overcome this error,
the eye of the observer should be parallel to the scale line of the apparatus.
Some precaution should be done during the experiment.
Firstly, the adding of phenol into the water should be done in fume cardboard
as the phenol is a carcinogenic substance. Besides, goggles and gloves should
be wear throughout the experiment. The boiling tube should be shake gently
while it is in the water bath to produce a uniform mixture of solution.
Conclusion
The critical solution temperature of the experiment is 65.5 oC.
The solubility of two partially liquid (phenol-water solution) is determined.
Question
1.
Explain
the effect of adding foreign substances and show the importance of this effect
in pharmacy.
The
addition of the foreign substances such as salt can give effect toward the
critical temperature and the phase separation. The addition of the salt will
reduce the miscibility of the phenol and water which cause the phase
separation. The water molecules will associate with the salt ions and hydrating
them. So, the simple ion will lower the tendency of the water to solvate the
phenol. The result of addition of the salt will be increasing the critical
temperature and the phenol on phenol rich side of the coexistence of the curve.
If the foreign substance are soluble in both liquid, the solution will be
soluble that called as blending. An example of this is when succinic acid is
added to the water-phenol mixture , succinic acid is soluble or completely
miscible in each water and phenol therefore it causes a blending of the liquids
making the mixture one phase. The solubility of the substance is important to
determine the purity of the substance.
References
1.
Martin's Physical Pharmacy
and Pharmaceutics 6th Edition
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