Practical 2: Phase Diagrams
Part B
Mutual Solubility
curve for phenol and water
INTRODUCTION:
A few types of liquid are miscible with each other at all different composition,
for example: ethanol and water. On the other hand, other liquids are partially
miscible with one another in limited proportions, for example: ether-water
system and phenol-water system. (Even though the phenol is not really a liquid,
but we consider it as a liquid because as we add in the first part of water,
the melting point is reduced until it becomes below room temperature to form a
liquid-liquid system.)
Generally, two liquids will be more miscible when the temperature is
increased until it reaches the critical temperature or consolute point of the
solution and above this point, the two liquid is miscible at any proportion.
Any pair of liquid is able to form a closed system, however the critical
temperature of the two solutions is not easy to be determined (i.e. the
temperature before the substance solidify or evaporate) with the exception of
nicotine and water system.
At any temperature below the critical point, composition of the two layers
of liquid in equilibrium is always a constant and it does not depend on the
different amount of the two phases. Miscibility of a pair of liquid that is
partially miscible with each other is affected by the presence of a third
component in the mixture.
OBJECTIVE: To investigate the mutual solubility curve for phenol and water.
APPARATUS: Test tube and test tube rack, parafilm, thermometer, water bath, pipette, beaker, stirrer, measuring cylinder
MATERIALS: Phenol and water
EXPERIMENTAL
PROCEDURES:
1) Five test tubes are prepared and placed on the test tube
rack.
2) Each test tube is labeled by A, B, C, D and E.
3) The total amount of liquids in the test tubes is
fixed to be 10ml and phenol are added in various percentages which are 8%, 20%,
40%, 60% and 80%.
Phenol concentration
|
8%
|
20%
|
40%
|
60%
|
80%
|
Amount of phenol (ml)
|
0.8
|
2.0
|
4.0
|
6.0
|
8.0
|
Amount of water (ml)
|
9.2
|
8.0
|
6.0
|
4.0
|
2.0
|
Table 1
5) The boiling tubes are heated in water bath.
6) Thermometer is placed into the tubes and sealed the tube
with parafilm as phenol is volatile substance.
7) The water in the beaker is stirred and the test
tube is shook during the heating.
8) When the turbid liquid becomes clear, the temperature for each of the tube is observed and recorded.
9) The tube was removed from the hot water and temperature was allowed to reduce gradually.
10) The temperature at which the liquid became turbid and two layers separated is recorded.
11) The average temperature for tube at which two phases were no longer seen or at which two phases exist is determined.
12) The graph of average temperature versus percentage of phenol is then plotted and the critical solution temperature is determined.
RESULTS:
Volume of Phenol (ml)
|
Volume of water (ml)
|
Temperature (oC)
|
Concentration of phenol
(%)
|
Concentration of water
(%)
|
||
When liquid become clear
|
When the liquid turn cloudy
|
Average
|
||||
0.8
|
9.2
|
41
|
39
|
40
|
8
|
92
|
2
|
8
|
67
|
64
|
65.5
|
20
|
90
|
4
|
6
|
68
|
66
|
67
|
40
|
60
|
6
|
4
|
63
|
61
|
62
|
60
|
40
|
8
|
2
|
35
|
37
|
36
|
80
|
20
|
Graph Of Concentration Of Phenol Over Temperature:
PRACTICE:
Explain the effect of
adding foreign substances and show the importance of this effect in pharmacy.
The miscibility of two components can definitely be affected by addition of foreign substances or materials. There are some components that are miscible with one another and vice versa. Some examples of substances that are miscible with each other are ethanol and water. When two components are miscible with each other, they will exist as single phase at a particular temperature with certain amounts for each component respectively. The maximum temperature that two components exist in different phase is known as critical temperature. Any amounts of components added after this temperature will give off a single phase which means that the components are separated into different phases and the conclusion is the miscibility of both components are increased. However, temperature is not the only factor that affects the miscibility of any mixture of components. There are many other factors that can affect the miscibility of the components. One of them is addition of foreign substances. It is proven that addition of salt or alkali salt can reduce the miscibility of the mixture of two components. The phase separation and the critical temperature will be strongly affected even with only a small amount of salt added. This means that the salt will enhance the separation of the phase and at the same time reduce the miscibility of the components. This is because water molecules will react with the salt ions to hydrate them and therefore, reducing the tendency of solvation of phenol by water molecules. This effect has some significance in pharmaceutical industry. One of them is in solving any problem that occurs during preparation of medicine that required phase separation. The best solvent to prepare medicine also can be chosen through application of this effect.
A phenol - water solution is used to determine the solubility of two partially miscible liquids. The group calculated the volume of water required to prepare the following mixtures with volume percentage ranging from 8% to 80% sample by using total of 10mL sample in each proportion. The different volume ratios of mixtures prepared are subjected to constant heating and cooling in order to gather the needed temperature necessary for the construction of the mutual solubility curve of phenol -water solution. The critical solution temperature is determined in the graph.
In this experiment, two-component systems containing liquid phases are discussed here. Phenol is partial miscible with water so they produce a two-phase system.However, addition of a sufficient amount of phenol to the water system would produce a single liquid phase because they are miscible, and the mixture is termed homogenous. The curve plotted in the graph temperature versus percentage of phenol in water in volume per volume shows the limits of temperature and concentration within which two liquid phases exists in equilibrium. The region outside this curve contains systems having but one liquid phase.
Since the phenol/water system is a two-component system containing liquid phases, the degrees of freedom are two as F=2-2+2=2. The two degrees of freedom are temperature and concentration.( At 5% of phenol in water at 25ºC, single liquid phase is produced. This is due to the less percentage of phenol in water and it is miscible with water completely.
From the graph plotted, at 58.3ºC, a minute amount of a second phase appears. The concentration of phenol and water at which this occurs is 11% by weight of phenol in water. At 68.5ºC, this is the upper consolute temperature which is the maximum temperature at which the two-phase region exists. A line drawn across the region containing two phases is termed a tie line; it is always parallel to the base line in two-component systems. All systems prepared on the tie line, at equilibrium, will separate into phases of constant temperature. These phases are termed conjugated phases. Tie line in a phase diagram use to calculate the composition of each phase in addition to the weight of the phases.)
Some precaution should be taken to obtain an accurate result. First of all, after the addition of phenol into the conical flask, film should be wrapped on the top of conical flask with thermometer in the middle to avoid evaporation of phenol. Besides that, due to phenol is acidic and carcinogenic compound, thus extra care should be taken to avoid harm to the human. Pipette instead of measuring cylinder is used to obtain more accurate volume required.
CONCLUSION:
The consulate temperature for
phenol/water system is 68ºC. Phenol is partial miscible with water and produce
one liquid phase system at certain temperature and concentration when pressure
is fixed. In the system above 68 ºC, combinations of phenol and water will be
completely miscible and one-phase liquid system yielded.
REFERENCES:
2. Physicochemical Principles of Pharmacy 4Th edition (2006), Alexander T Florence and David Attwood, Pharmaceutical Press.
3. Martin’s Physical Pharmacy and Pharmaceutical Sciences, 4th edition (1993), Patrick J. Sinko, Lippincott Williams and Wilkins.
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