TITLE:
Mutual solubility curve for phenol and water
OBJECTIVE:
To determine the critical solution temperature of water-phenol system and to
study the mutual solubility curve for phenol and water
DATE
OF EXPERIMENT: 04/11/2014 (Tuesday)
INTRODUCTION:
Mutual solubilities of partially
miscible mixture is influenced by temperature. Phenol and water is consider as
partial miscible, which is the formation of two layers when certain amounts of
liquids are mixed. A portion of the condensed phase diagram is plotted.
The curve above shows the
limits of the temperature and concentration within which two liquid phases
exist in equilibrium. The region outside this curve contains systems having but
one liquid phase while region inside the curve contain systems having two
liquid phase.
The maximum temperature on the
curve which is the maximum temperature at which the two-phase region exists is
termed the critical solution temperature.
Most probably, any pair of
liquids can form a closed system, in which both upper and lower critical
solution temperature exist, but to determine both the temperature is not easy
(except for nicotine and water).
APPARATUS:
·
Boiling tube
·
Measuring cylinder
·
Parafilm
·
Boiling tube rack
·
Thermometer
·
Water bath
CHEMICALS:
·
Distilled water
·
Phenol
PROCEDURES:
1.
Seven 20 mL mixtures of phenol and water
containing 8%, 11%, 25%, 35%, 50 %, 63%, 70% and 80% concentration of phenol
are prepared in seven boiling tubes.
2.
The boiling tubes are labelled and
sealed with parafilm.
3. A
thermometer is poked through each of the parafilm into the boiling tubes to
measure the mixtures’ temperature.
4. The boiling tubes are placed into the water bath.
5. The water is stirred constantly and if possible, the boiling tubes are
shaken well.
6. The temperature for each of the tubes at which the turbid liquid becomes
clear are observed and recorded.
7. The tubes are removed from the water bath and are allowed for
temperature to reduce gradually.
8. The temperature at which the liquid becomes turbid and two layers are
separate are observed and recorded.
9. The average temperature for each tube at which two phases are no longer
seen or at which two phase exist are determined.
10. The graph of temperature
at complete miscibility against phenol composition are plotted.
11. The critical solution temperature is determined.
RESULTS:
|
Phenol
Coposition (%)
|
Volume
of phenol (mL)
|
Volume
of water (mL)
|
Temperature
(ͦC)
|
||
|
Clear
|
Cloudy
|
Average
|
|||
|
8
|
1.6
|
18.4
|
50
|
42
|
46
|
|
11
|
2.2
|
17.8
|
54
|
49
|
51.5
|
|
25
|
5
|
15
|
62
|
61
|
61.5
|
|
35
|
7
|
13
|
64
|
62
|
63
|
|
50
|
10
|
10
|
68
|
67
|
67.5
|
|
63
|
12.6
|
7.4
|
65
|
63
|
64
|
|
70
|
14
|
6
|
64
|
63
|
63.5
|
|
80
|
16
|
4
|
50
|
50
|
50
|
QUESTIONS:
1. Plot the
graphs of phenol composition (horizontal axis) in the different mixtures
against temperature at complete miscibility. Determine the critical solution
temperatures.
Critical solution temperature of
water-phenol system is 67.5 ̊C.
2.
Discuss
the diagrams with reference to the phase rule.
Phase rule is a useful device for relating the
effect of the least number of independent variables (eg. temperature, pressure
and concentration) upon the various phases (eg. solid, liquid and gaseous) that
can exist in an equilibrium system containing a given number of components.
Phase is expressed as
F=C-P+2
Where,
F
is the number of degrees of freedom in the system
C
is the number of components
P
is the number of phases present.
In this experiment, we have
two components which is the phenol and water. When mixture of phenol and water
is homogenous, the degree of freedom, F = 2 − 1 + 2 = 3. However, since the
pressure is fixed for this system, F is reduced to 2. Therefore, to define the
system, we need to fix temperature and concentration. When phenol and water are
immiscible, where P = 2, F = 2 - 2 + 2 = 2. However, since the pressure is
fixed for this system, F is reduced to 1.Thus, only temperature is needed to
define the system.
With a two-component
condensed system having one liquid phase, F=3 because F=2-1+2. However, the
pressure is fixed so F is reduced to 2, hence we have to fix both temperature
and concentration to define the system. When two liquid phases are present, F=2
because 2-1+2=2, but F is reduced to 1 as pressure is fixed. Hence, only
temperature is needed to complete define the system.
3.
Explain
the effect of adding foreign substances and show the importance of this effect
in pharmacy.
The
addition of foreign substances to binary system, in this case, the water-phenol
system will results in ternary system.
If the foreign substance is
soluble only in one component, or if solubilities in both liquids are very
different, the mutual solubility will decrease. Thus, the present of foreign
substances will lead to the raise in upper consolute temperature and lowered
the lower consolute temperature.
However, if the foreign
substance is soluble in both liquids, the solution will be soluble that called
as blending. The mutual solubility will be increased. For example, succinic
acid is added to the water-phenol mixture. The upper consolute temperature is
lowered because of negative salting out effect while the lower consolute
temperature is raised.
Addition of many common salts
such as sodium chloride and naphthalene can reduce the miscibility of phenol
and water. It is due to the tendency of water molecules to associate with ions,
hydrating them. In that way, simple ions reduce the tendency of water to
solvate phenol. Thus, in pharmaceutical industry, salt may be added to make the
organic material form a phase separate from the salty aqueous phase. This
procedure may be familiar as "salting out."
The effect of adding foreign
substances is important to the industrial production of highly concentrated
solutions of tar acids (phenols and cresols) used as disinfectants. Besides,
the solubility of the substance is important to determine the purity of the
substance.
DISCUSSION:
The
graph obtained from the experiment is dome shape with an upper critical
solution temperature. It shows the phase boundary line that is the limits of
temperature and concentration within which two liquid phases exists in
equilibrium. The region outside the curve is one liquid phase while region
inside the curve is two liquid phases.
When the quantity of phenol
increase gradually, the amount of phenol-rich phase continually increases but
the amount of water-rich phase continually decreases. Eventually, it will form
a single phenol-rich liquid phase.
From the experiment, the critical
solution temperature of water-phenol system is 67.5 ° C which is slightly
different from the theoretical value (66.8°C). Beyond this temperature, the two
liquids are miscible in all proportion. The deviation of
critical
solution temperature may due to the evaporation of phenol before we sealed the
top of boiling tubes. Besides, there may be some delay of time when we take the
temperature when two phases appear or two phases disappear.
Precautions
should be taken during the experiment. Firstly, do cover the exposed body parts
by wearing mouthpiece, safety goggles, gloves and laboratory coat throughout
the experiment for protection because the phenol is carcinogenic compound. Before
the beginning of experiment, do make sure all your equipment is in good order
and check all glassware and containers for cracks. All the equipment should be washed
properly with distilled water before taking them in use as the presence of any
other chemical can be the reason for wrong measurement. In all cases, the eyes
must level with the bottom of meniscus to avoid parallax error. Besides, do make
sure all the boiling tubes are sealed tightly with parafilm to avoid the evaporation
of phenol when it mix with water.
CONCLUSION:
Phenol and
water is partially miscible. The critical solution temperature of water-phenol
system is 67.5 ̊ C.
REFERENCES:
1. Remington:
The Science and Practice of Pharmacy, 21st edition, Lippincott
Williams & Wilkins, page 271
2. A Textbook of Physical Chemistry, A. S. Negi,
S. C. Anand, page 373
3. http://www.scribd.com/doc/137136642/Phenol 
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