Title:
Mutual Solubility Curve for Phenol and Water
Date:
7th November 2016
Objectives:
1. To determine the solubility of two partially liquids (phenol
– water solution)
2. To construct the mutual solubility curve and determine the
relationship between the temperature and solubility of the liquids
3. To determine the critical solution temperature
Introduction
Some liquid are completely
immiscible (eg. Oil and water) while some are completely miscible in all
proportions (eg. Ethanol and water) . However, many liquid mixtures fall between these two extremes. If
you shake equal volumes of two of these liquids together, you often get two
layers with unequal volumes. These liquids are “partially miscible”.
As the temperature rises, both liquids become more
soluble in each other. They reach a mutual solubility temperature or critical solution temperature. Above that point, the
mixture becomes homogeneous, where one layer will be formed. Below that point,
the mixture separates into two layers.
Phenol is also soluble in
water to some extent due to its ability to form hydrogen bonding with water
molecules. Nevertheless, the large part of phenol molecule is phenyl group that
is non-polar. Hence its solubility is limited in water. However the polarity of
this part increases in phenoxide ion when the temperature is raised, and hence
the liquids will be more soluble.
At any temperature below
the critical solution temperature, the composition for two layers of liquid in
equilibrium state is constant and does not depend on the relative amount of
these two phases. The mutual solubility for a pair of partially miscible liquid
in general is extremely influenced by the presence of third component.
Apparatus
Boiling tube, Test
tube, Measuring cylinder, 5ml pipette, 1ml pipette, Water bath, Thermometer
Materials
Distilled water, Phenol
Procedure
1. Five
boiling tube is prepared and labelled as A, B, C, D and E
2. The
boiling tubes are filled with different amount of water and phenol with the
respective percentage.
a. Boiling
tube A with 8% of phenol
b. Boiling
tube B with 30% of phenol
c. Boiling
tube C with 50 % of phenol
d. Boiling
tube D with 70% of phenol
e. Boiling
tube E with 80% of phenol
3. Heat the boiling tubes with water bath. The boiling tubes
were swirled and shaken well.
4. The tubes were observed and temperatures were recorded when
the turbid becomes clear.
5. The tubes were removed from the hot water and the temperature
was allowed to reduce. As soon as the liquid becomes turbid and two separate
layers were form, the temperature is recorded.
6. Steps 1 – 4 are repeated.
7. By using the temperature obtained, the average temperature
for each tubes at which the two phases were no longer
seen or at which two phases were exist were determined.
Result
|
SET
|
PERCENTAGE
OF PHENOL (%)
|
PERCENTAGE
OF WATER (%)
|
TEMPERATURE
WHEN MIXTURE BECOME ONE LAYER (°C)
|
TEMPERATURE
WHEN MIXTURE BECOME TWO LAYER (°C)
|
AVERAGE
TEMPERATURE (°C)
|
|
1
|
8
|
92
|
65
|
X
|
65.0
|
|
2
|
30
|
70
|
74
|
72
|
73.0
|
|
3
|
50
|
50
|
77
|
75
|
76.0
|
|
4
|
70
|
30
|
71
|
68
|
69.5
|
|
5
|
80
|
20
|
X
|
X
|
X
|
GRAPH
Discussion
Phase
rule is a device that is used to relate the effect of the least number of
independent variables upon various phases that can exist in an equilibrium
system which have a given number of components. The phase rule can be expressed
as F= C-P+2 where F is the number of degrees of freedom in the system, C is the
number of components and P is the number of phases present. In this experiment,
phenol and water is used as the components where phenol is partial miscible
with water. When phenol is miscible with water at certain condition, the number
of degrees of freedom in the system, F=2-1+2=3 . Since the pressure is fixed for
this system which is the atmospheric pressure, F is reduced to 2. This means
that we need to fix both temperature and concentration to define this system.
When phenol is immiscible with water at certain condition, the number of
degrees of freedom in the system ,F =2-2+2=2 . Since the pressure is also fixed
for this system which is the atmospheric pressure,F is reduced to 1. This means
that we only need to fix the temperature to define the system.
After
the experiment , a graph of temperature at complete miscibility versus phenol
composition in different mixture is plotted. A n-shaped graph is obtained. This
curve shows the limits of temperature and concentration within which phenol and
water exist in equilibrium. The region outside the curve shows that phenol is
miscible with water(1 liquid phase) while the region within the curve shows
that phenol is immiscible with water(2 liquid phase).The maximum temperature at
which the 2 liquid phase exist is called critical solution temperature. The
critical solution temperature in this experiment is 76.2°c.
The
curve that is obtained from the experiment have some slight deviation compared
to the actual mutual solubility curve. This occur because there are some error
that have been done when conducting the experiment. Firstly, the tube are not
tightly sealed. The tube together with the thermometer should be tightly sealed
to prevent heat loss to the surrounding that will affect the reading of the
temperature of the mixture. This can also prevent the evaporation of the phenol
when it is heated. Besides that, the reading of the temperature should be taken
immediately after the mixture become miscible or immiscible because the
temperature of the mixture increase and drop rapidly. Lastly, parallax error
might occur when taking the reading of the thermometer. The eyes of the
observer should be perpendicular to the scale of the thermometer to prevent
parallax error.
Questions
Explain the effect of adding foreign
substances and show the importance of this effect in pharmacy.
ANS: The addition of foreign substances may affect the
critical solution temperature. When the substances added dissolve in only one of the two liquid, the
mutual solubility will decreased. The temperature at which the system become 1
liquid phase will increased if the system has upper critical solution
temperature and temperature lowered for
system that has lower critical solution temperature. This concept is important
in pharmacy as its help the pharmacist to select suitable solvent for a drug
and help overcome problem arise during preparation of drugs.
Conclusion
Phenol and water are immiscible unless
it meets certain temperature at particular concentration. As the concentration
of phenol in the mixture increase, the temperature for the phenol to become
miscible with water increase until it reach the critical solution temperature
which is 76.2°c. After the critical solution temperature, the temperature of
the mixture drops even though the concentration of the phenol increase.
References
1)Lecture note (Phase diagram 1)
2) College
Practical Chemistry, by V K Ahluwalia, Sunita Dhingra (2005)
3) https://socratic.org/questions/what-is-mutual-solubility-temperature
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