TITLE:
Mutual solubility curve for phenol and water
AIM:
To study phase rule and construct the mutual solubility curve of a pair of partially miscible liquids, which are phenol and water
DATE OF EXPERIMENT:
7 November 2016
INTRODUCTION:
The number of homogeneous, mechanically separable and physically distinct parts of a heterogeneous system is known as the number of phases, P, of a system.
F=C-P+2 (1)
F= The number of degree of freedom in the system
C= The number of components in the system
P= The number phases present in the system
Equation (1) is known as Phase Rule that can relate phases, components and degree of freedom in a system.
A few liquids are miscible with each other in all proportions, for example; phenol and water. Meanwhile others have limited proportions of miscibility in other liquids, for example; ether-water and phenol-water. It is noted that phenol is not really liquid, but is considered to be so since the addition of the first part of water reduces the solid’s melting point under room temperature to produce a liquid-liquid system. When 2 partially miscible liquids are mixed and shaken together, we get 2 solutions of different compositions. For example, on shaking phenol and water, we get 2 layers, in which the upper layer is a solution of water in phenol, and the lower layer is a solution of phenol in water. At a fixed temperature, the composition of each solution is fixed, and both the solutions are in equilibrium.
Two solutions of different compositions existing in equilibrium with one another are known as conjugate solutions. Above a particular temperature, such solutions are completely miscible in all proportions. Such a temperature is known as the Critical Solution Temperature (CST) or Consolute Temperature. As the mutual solubility increases with temperature in this particular case, it is known as Upper Consolute Temperature. In this experiment, we will plot the Mutual Solubility Curve by observing the temperature of two miscible liquids, water and phenol.
If we have two liquids A and B and mix them, we get a mixture of composition c1. At any temperature t1 (or below t1), the 2 liquids separate into 2 layers of different compositions. Above t1 , the two layers are completely miscible. Thus, the point corresponding to temperature t1 and composition c1 is known as the miscibility point. If we take another mixture of A and B of composition c2, we can find out the temperature (say t2) above which the last 2 layers become completely miscible. Similarly, we can find out corresponding temperatures for a number of mixtures of A and B. If a curve is plotted with temperature (oC) as ordinate (y-axis) against concentration (% by weight) as abscissa (x-axis), a mutual solubility curve will be obtained.
CHEMICAL AND APPARATUS:
Phenol, water, boiling tube, thermometer, beaker, water bath, parafilm
PROCEDURE:
1. Mixture of
phenol and water was prepared in boiling tubes in the way that phenol was added
into the water in various percentages which are 8%, 20%, 50%, 60% and 80%.
2. The total amount of two liquids in the boiling tubes was
fixed to be 30ml and the boiling tubes were labeled with 8% phenol 92% water
(1), 20% phenol 80% water (2), 50% phenol 50% water (3), 60% phenol 40% water
(4) and 80% phenol 20% water (5).
3. Then,
boiling tube (1) was heated in hot water and the mixture was stirred.
4. The
temperature at which the turbid liquid became clear was recorded.
5. The
boiling tube was then cooled gradually and the temperature at which the liquids
became turbid again forming 2 separated layers was recorded.
6. Finally,
steps 3-5 were repeated for boiling tubes (2) to (6).
7. A
graph of temperature at complete miscibility against phenol composition in the
different mixtures was plotted. The critical solution temperatures are
determined.
RESULTS:
Phenol composition (%)
|
8
|
20
|
50
|
60
|
80
|
Volume
of phenol (ml)
|
2.4
|
6.0
|
15.0
|
18.0
|
24.0
|
Volume
of water (ml)
|
27.6
|
24.0
|
15.0
|
12.0
|
6.0
|
Temperature
of single- phase (°C)
|
82
|
76
|
81
|
72
|
40
|
Temperature
of double- phase (°C)
|
43
|
62
|
79
|
61
|
34
|
DISCUSSION
:
In
this experiment , the n-shaped of graph is obtained when the average
temperature versus composition of phenol
is plotted . The curve shows the limit of the
temperature and concentration within which two liquid phases (phenol and
water) exist in equilibrium . The region inside the curve contain system that
have two liquid phases while the region outside the curve contain system that
have one liquid phase.
The
reading of the thermometer for the single layer is obtained when the mixture turns clear by
heating it in water bath and the reading of thermometer for the double layer of
phenol and water is obtained when it turns back to two separate layer by
cooling it down .
The
maximum temperature at which the two phase region exists is called critical
solution or upper consolute temperature . Based on our graph , the upper consolute temperature is 82 ͦC . All combination of phenol and water
above this temperature are completely miscible and contain system that have one
liquid phase .
When
the composition of phenol in water is less than 8% , the phenol and water are
completely miscible and exist as one liquid phase . Same thing happen when the
composition of phenol is more than 80% ,the phenol and water exist as a single
phase . Between 8% to 80% composition of phenol , phenol and water exist as two
phase system . At first , it is a water-rich phase but the increasing amount of phenol into the system will cause
the amount of phenol-rich phase to be increased . At the same time , the amount
of water-rich phase will be decreased .
The
phase rule applied to calculate the number of degree of freedom in the two
component system is as below :
F=C-P+2
=2-1+2
=3
Where
; F=Degree of freedom
C=Number
of component
P=Number
of phase exist
As
the pressure , 1 atm is fixed , F is reduced to 2 and it is necessary to fix
both temperature and concentration to define the system .
As
mentioned earlier , the upper consolute temperature is 82 ͦC which is slightly deviated from the
theoretical temperature value (66. 8 ͦC)
. This is happened because of some errors that occurred while conducting the experiment
.The first error that possibly occured is the test tubes are not sealed tightly
which causes the phenol to evaporate and
reduce the concentration of phenol . Besides , we did not take the
reading of thermometer as soon as the mixture becomes single phase and two
phase because the temperature will decrease rapidly after taken out from the
water bath .Next , parallax error might occur while measuring the amount of
phenol and water by measuring cylinder and also during taking the reading of
thermometer .
Thus
, there are some precautions that need to be taken during experiment such as
sealed the test tubes tightly using parafilms
to avoid evaporation of phenol .
Be aware and immediately take the reading of thermometer when they turns cloudy
and clear . Parallax error can be
avoided by ensuring that the eye is perpendicular to the meniscus while taking
reading and we can replace measuring cylinder with burette to obtain the
accurate volume of phenol and water .
CONCLUSION
:
The
phenol-water system is a two component
system . The upper consolute temperature of this experiment is 82 ͦC
where any combination of phenol and water above this temperature is completely
miscible and yield one-phase liquid system . Temperature and concentration need
to be fixed in order to define the system .
REFERENCES :
1.Physiochemical Principles of Pharmacy (4th) edition by Alexander T Florence and David Attwood
REFERENCES :
1.Physiochemical Principles of Pharmacy (4th) edition by Alexander T Florence and David Attwood
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