Mutual Solubility Curve for Phenol and Water

OBJECTIVES:

1. to determine the solubility of two partially liquids (phenol – water solution)
2. to construct a mutual solubility for the pair
3. to determine their critical solution temperature.

INTRODUCTION:

A few liquids are miscible with each other in all proportion, for example: ethanol and water. Others have miscibility in limited proportions in other liquids, for example: etherwater, phenol-water. (Here 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).

Generally both liquids become more soluble with rising temperatures until the critical solution temperature or consolute point is attained, and above this point the liquids completely miscible. There is a big possibility that any pair of liquids can form a closed system where both upper and lower critical solution temperatures exist, however it is not easy to determine both the temperatures (before the substance freezes or evaporates) except for nicotine and water.

At any temperature below critical solution temperature, the composition for two layers of liquids in equilibrium state is constant. The mutual solubility for a pair of partially miscible liquids in general is extremely influenced by the presence of a third component.

APPARATUS:
Boiling tubes, test tube rack, measuring cylinder, 5 mL pipette, 1 mL pipette, water bath, thermometer.

MATERIALS:
Distilled water, phenol.

PROCEDURE:

1. Eight boiling tubes were prepared and labeled as A,B,C,D,E,F, G and H respectively. The boiling tubes was filled with different amount of phenol and water. Boiling tube A filled with 8%, B 11%, C 25%, D 35%, E 50%, F 63% G 72% and H 80% of phenol respectively and distilled water was added until every boiling tube contains 20 mL of the mixtures. Volume of distilled water and phenol are as follows:

Water (mL)		18.4	17.8	15.0	13.0	10.0	7.4	5.6	4.0
Phenol (mL)		1.6	2.2	5.0	7.0	10.0	12.6	14.4	16.0

2. Heated the boiling tubes with the water bath. The boiling tubes were swirled and shaken well. 
3. Once the mixtures becomes a single phase (totally clear), the temperatures are recorded. 
4. The tubes were removed from the hot water and the temperature was allowed to decrease. Then the temperature were recorded when the liquid become turbid and two separate layers were formed again. 
5. Steps 1 to 4 are repeated.
6. By using the temperatures obtained, the average temperature for each tubes at which the two phases are seen as a single phase or at which two phases are separate were determined. 

RESULTS:

Test tube	Single-phase (°C)	Two-phase (°C)
A	55	X
B	59	46
C	74	64
D	77	72
E	79	70
F	70	60
G	65	X
H	55	X

DISCUSSION

The graph shows the temperature against the percentage by weight of phenol in water. Phase diagram is divided into two regions by the transition curve.In the region inside the curve two phases are separate and outside it only single phase exists.

In phenol-water system,the maximum temperature (79 ˚C  at which the two phase region exists Is called the critical solution temperature or upper consolute temperature.

The phase rule is P + F = C + 2, where

• P = number of phases that can coexist, to
• C = number of components making up the phases, and
• F = degrees of freedom.

Phase rule can also be expressed as F=C-P+2. In this experiment, we have 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. This means that we need to fix both temperature and concentration to define this system. When phenol and water are immiscible with each other, the degree of freedom is calculated by F = 2 − 2 + 2 = 2. Since this is a condensed system which means the 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.

Based on the graph shows the temperature at complete miscibility against the percentage by weight of phenol in water. The temperature when the two liquid phases become one liquid phase (complete miscibility) increase as the composition of phenol in water increase until the maximum temperature; also known as the critical temperature. Phenol can be soluble in water at certain temperature or when the composition of the phenol is much higher than the water.

At room temperature, a tube contains two liquid phases, one more dense than the other. The tube is heated in a water bath until the two phases merge. The temperature at which they merge is the "clearing temperature," also known as the "cloud" temperature, and lies on the liquid-liquid coexistence line. By using several sample tubes, one obtains several points on the coexistence line. 

Critical temperature in this experiment can be define as the maximum temperature at which the liquid phase can be converted into a liquid by an increase in temperature. From the results obtained, the critical temperature is 79 ˚C. The result shows a little bit higher than the theoretically value which is 68 ˚C. This happened due to some errors that we might get into during conducting this experiment. One of those errors is when warming the test tubes in the water bath, the exact temperature at which the two phases become one could not be seen immediately due to sealing film blocking the thermometer. Also the sealing film is not applied properly and leaking may have occurred.

i.   The glass wares must be rinsed before used.

ii. The temperature must be taken immediately to get accurate results.

CONCLUSION:
The critical solution temperature peaks at 79°C. A single phase is observed at that temperature. the solubility of phenol in water is depending on the temperature and the percentage of phenol in water by volume.

REFERENCES:
1. Sinko, Patrick J., Martin's Physical Pharmacy and Pharmaceutical Sciences,  5th ed.,  Lippincott Williams & Wilkins, 2005
2. http://jeplerts.wordpress.com/2008/12/21/partially-miscible-liquids-determination-of-mutual-solubility-of-phenol-water/