Mutual Solubility Curve for Phenol and Water

DATE OF THE EXPERIMENT:4/11/2014

TITLE:  Phase Diagram – Mutual Solubility Curve for Phenol and Water.

OBJECTIVES:   

a) to measure the miscibility temperature of several water and phenol mixtures

b) to determine the mutual solubility curves of phenol and water.

APPARATUS AND MATERIALS:

Measuring cylinder, thermometer, beaker, boiling tube, distilled water, phenol, water bath

INTRODUCTION:

                     

          

            

     Phenol known as carbolic acid, hydroxybenzene  and phenyl alcohol, is produced at the rate of millions of tons per year, mostly from isopropyl benzene. Phenol is a starting material in the manufacturer of plastics and drugs. It was used an antiseptic beginning in the 1860’s. However, phenol is poisonous. The phenol-water mixtures used in this lab are concentrated and dangerous by contact or ingestion. Aqueous phenol solutions have been used pharmaceutically. At low and high percentages of phenol , water and phenol mix completely, forming a single liquid phase. Above the critical temperature, phenol and water are completely miscible. The water- phenol phase diagram contains a solid phase at high percent phenol, near and somewhat above room temperature. That part of the diagram is not shown in the figure. The independent variable in the phase diagram is composition. Composition is sometimes given as mass percent. This experiment will refer to composition as mole fraction phenol.

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

PROCEDURE:

1.  8 boiling tubes was prepared and each tube were filled with a different amount water and phenol.
2. Then, the tubes  were heated  in a beaker containing water to increased the temperature.
3. The water were stirred and shaken.
4. The temperature for each of the tubes were observed and recorded at which the turbid liquid becomes clear.
5. The tubes were then removed from hot water and allowed for the temperature to reduce gradually.
6. The temperature was recorded at which the liquid become turbid and two layers were separated.
7. Then, the average temperature for each tube at which two phases are no longer seen or at which two phases exist were determined.

RESULT:

Graph of Mutual Solubility Curve of Phenol and Water

QUESTIONS AND ANSWERS:
1. Plot the graphs of phenol composition (horizontal axis) in the different mixtures against temperature at complete miscibility. Determine the critical solution temperatures.

The critical solution temperature 78ºC.


2. Discuss the diagrams with reference to the phase rule.

The graph above in the results shows the graph of temperature at complete miscibility of solution against percentage of phenol composition in the solution. The region outside the curve shows that the solution is in complete miscibility and has only one phase, whereas the region inside the curve indicate the two phase system of the solutions. According to the phase rule,  
F=C-P+2

F is degree of freedom

C is numbers of component

P is number of phase exist
F=2-1+2, thus the degree of freedom for this system is 3. This show that 3 intensive variable must be fixed in order to describe the system completely. As the pressure is fixed, F reduces to 2, and it is necessary to fix both temperature and concentration of phenol in the solution to define the system.


3. Explain the effect of adding foreign substances and show the importance of this effect in pharmacy.

Solubility of a binary system is very important in preparation of drugs in pharmacy. It is very common for two or more liquids to be mixed together in a pharmacy to make a solution, therefore the pharmacist needs to know what liquids can be mixed together without precipitation occurring. The addition of foreign substance to a binary system results in a ternary system. The degree of freedom and miscibility of the two liquid will be affected. If the substance reduces the miscibility of the two liquid, the dispensed medicine may changes its nature and no longer suitable for consumption. Besides, the therapeutic effect of some drug will be reduced and may be harmful to human body. This condition may be arising due to contamination in extemporaneous preparation when the place of medicine preparation is not hygienic. If the substance increases the miscibility of the liquids, the dispensed medicine may be somewhat helpful to the absorption of the drug in the human body.

DISCUSSION:
From the experiment that carried out, we plotted the graph of average temperature versus percentage of phenol. After graph has been plotted, we get an 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. At the 0% and 100% of phenol, two liquid separations do not occur due to there is no phenol and water molecules respectively of each of the percentage.The 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. Within the region of the curve, there will be existence of two liquid phases. As we add the quantity of phenol gradually, the amount of phenol-rich phase continually increases and the amount of water-rich phase continually decreases. At last, 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 theoretical critical solution temperature in this experiment is 68.0˚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, the graph is slightly deviated from the theoretical graph. This may be due to some of the errors or mistakes have been occurred during the experiment. First and foremost, when we sealed the tubes, we need to ensure that all the tubes are tightly sealed to prevent evaporation of phenol once the phenol is mix with water. Evaporation of phenol need to be avoided as this may affect the result of this experiment. Besides, when we insert the thermometer into the tubes, we have to make sure that the test tubes are still tightly sealed. If the test tubes are not sealed tightly, the heat will escape to the surrounding when we measured the temperature. This may affect the accuracy of the results. Moreover, we must be careful when we are taking the reading of temperature when heating the mixture and cooling the mixture. This is because the temperature will increase rapidly or drop rapidly. When the turbid liquid in the tubes become clear and homogeneous, we should take the reading immediately. After we left the tubes to cool down, the temperature must be recorded immediately when the liquid become turbid again and form 2 layers. This will help us to get a more accurate reading and plotted a more smoothly graph. Besides, parallax error may occur when measure the volume of components (water and phenol) in the mixture by using measuring cylinder, so the desired volume may not be obtained and this careless mistake may contribute to the inaccuracy of the result. Therefore, pipette is suggested to use during the experiment so that desired volume will be obtained and further contribute to the precise result of critical solution temperature’s value.

CONCLUSION:
The critical solution temperature is 78ºC. The plotting of mutual solubility curve of water-phenol system is achieved.

REFERENCE:

1. Martin's Physical Pharmacy and Pharmaceutics 6th Edition
2. http://www.d.umn.edu/~psiders/courses/chem4643/labinstructions/phenol.pdf
3. http://www.sciencedirect.com/science/article/pii/0378381295968943