DATE : 3 / 11 / 2015
TITLE
PART B:
Mutual Solubility Curve for Phenol and Water
OBJECTIVE
The objectives of the experiment are to determine
the critical solution temperature for the phenol-water system and to construct
the mutual solubility curve of phenol-water system.
INTRODUCTION
Ethanol and water are liquids that miscible with
each other in all proportions while phenol and water have miscibility in
limited proportions in other liquids. Basically, both liquids become more
soluble with rising the temperature until achieve the critical solution
temperature. Above this point, the liquids become completely miscible. The
phenol-water system is a suitable example to illustrate the variation of
solubility with temperature. At low and high percentages of phenol, water and
phenol mix completely forming a single liquid. However, at the intermediate
compositions and below the critical solution temperature, mixtures of phenol
and water separate into two liquid phases. At any temperature below the
critical solution temperature, the composition for 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 the pair of partially miscible
liquids in general is extremely influenced by the presence of a third
component.
MATERIAL
Phenol, water
APPARATUS
Test tubes, test tube rack, thermometer, parafilm,
aluminium foil, water bath, beaker, measuring cylinder
PROCEDURE
- 1. Mixtures of phenol and water in test tubes was prepared where the phenol was added in water in various percentages from 8%, 20%, 40%, 60% and 80%.
- 2. The total amount of both liquids in the test tubes were fixed to be 20 mL and labelled with A, B, C, D, and E.
- 3. The test tube A containing 1.6 mL of phenol and 18.4 mL of water were heated in water bath and stirred the mixtures.
- 4. The temperature at which the turbid liquid became clear was observed and recorded.
- 5. The test tube then was removed from the water bath and cooled gradually.
- 6. Temperature at which the liquids became turbid again and forming two separated layers was observed and recorded. The test tube was heated again and the average temperature for heating and cooling was recorded.
- 7. Steps 3 until 6 were repeated for test tubes B, C, D and E.
- 8. A graph of phenol composition in the different mixtures against temperature at complete miscibility was plotted. The critical solution temperature was determined.
RESULT
Percentage of phenol
(%)
|
Volume of phenol
(ml)
|
Volume of
water
(ml)
|
Temperature (oC)
|
Average temperature
(oC)
|
|
During Heating
|
After Cooling
|
||||
8
|
1.6
|
18.4
|
60
|
10
|
35
|
20
|
4
|
16
|
71
|
65
|
68
|
40
|
8
|
12
|
76
|
64
|
70
|
60
|
12
|
8
|
69
|
57
|
63
|
80
|
16
|
4
|
60
|
50
|
DISCUSSION
Phase rule is a useful device
for relating the effect of the least number of independent variables like
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.
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 component
P =the number of phases
present
Ethyl alcohol and water are
completely miscible both as vapours and liquids. A system consists of phenol
and water exhibit partial miscibility, which lies between two extremes (the
systems of miscible and completely immiscible).
In this experiment, two components
which is the phenol and water and phases depend on the conditions in which the
experiment was conducted. When phenol and water are miscible with each other at
a particular condition, the degree of freedom, F = 2 − 1 + 2 = 3. Since the
pressure is fixed for this system, F is reduced to 2. Both temperature and
concentration need to be fixed to define this system. When phenol and water are
immiscible with each other, the degree of freedom, F = 2 − 2 + 2 = 2.Pressure
of the system is fixed, thus the F is reduced to 1. This means that we need to
fix the temperature only to completely define the system.
From the experiment that
carried out, we plotted the graph of average temperature versus percentage of
phenol. After graph has been plotted, we get a incomplete n-shaped-liked graph.
The curve shows the limits of temperature and concentration within which the
two liquid phases (phenol and water) exist in equilibrium. Region outside the
curve contains system having one liquid phase. This means that the phenol and
water becomes miscible and exists as one liquid phase at the region outside the
curve. The region under the of the curve, there will be existence of two liquid
phases. The quantity of phenol is gradually increased, the amount of
phenol-rich phase continually increases and the amount of water-rich phase
continually decreases. At the last test test tube, a single phenol-rich liquid
phase is formed. The maximum temperature at which the two phase region exists
is called the critical solution temperature. The critical solution temperature
in this experiment is 72.0˚C. During this experiment, we are measuring the
temperature of the phenol-water system at miscible and temperature at which two
phases separated.
From the results that we
obtained, some of the points in the graph are slightly deviated from the graph.
Parallax error during reading the scale of the thermometer is one of the
possible error which causes the deviation. Then, covering the mouth of the test
tube with aluminium foil is one of the precaution as phenol is a carcinogenic
chemical. The boiling tube should be shaken gently while it is in
the water bath to produce a uniform mixture of solution.
CONCLUSION
The critical temperature of the
solution peaks at 72 oC. Water and phenol
are two component system. Phenol is soluble in water at certain temperature as
it form clear solution and become immiscible when it is cooled down as the
solution showing two layer in the test tube.
