Experiment 2 - Phase Diagram (Part B)

TITLE

Phase Diagram ( Mutual Solubility For Phenol and Water )

DATE

17^th April 2014

OBJECTIVES

1. To determine the solubility of two partially liquid (phenol and water)
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 proportions.  An example is phenol and water.  Phenol and water can exists in one liquid phase as well as two liquid phase.  Theoretically, the combination of phenol and water above the the temperature 66.8 degree Celsius are completely miscible and yield only one phase.The maximum temperature at which two liquid phase can exist is termed as the critical temperature or known as the upper consolute temperature.  The composition for two layers of liquid in equilibrium state is constant and does not depend on the relative amount of these two phases at any temperature below the critical solution temperature.  The presence of third component will influence the mutual solubility for a pair of partially miscible liquid. 

APPARATUS AND MATERIALS

Phenol

Distilled water

Test tube

Test tube rack

Measuring cylinder

Thermometer

 

Water bath

Dropper

PROCEDURES

1. A tightly sealed tubes containing amounts amounts of phenol and water are given to produce a phenol concentration scale between 8% to 80%.
2. 5 test tubes are labeled as 1, 2, 3, 4 and 5 respectively.
3. Test tube 1 is filled with 8% of phenol, test tube 2 with 11% of phenol, test tube 3 with 37% of phenol, test tube 4 with 63% of phenol and test tube 5 with 82% of phenol.
4. Water is added into all the 5 test tubes until a volume of 10ml is reached.
5. The test tubes are heated. The test tubes are shaken as well.
6. The temperature for each of the test tube at which the turbid liquid becomes clear is observed and recorded.
7. The test tubes are removed from hot water and allowed to cool.
8. The temperature at which the liquid becomes turbid and two layers are separated is recorded.
9. The average temperature for each tube at which two phases are no longer seen or at which two phases exist is determined.

RESULTS

QUESTIONS

1.   Plot the graph of phenol composition (horizontal axis) in the different mixture against temperature at complete miscibility. Determine the critical solution temperatures.

The critical solution temperature is 68.5ºC.

2.      Discuss the diagram with references to phase rule.

The graph above is a two component system containing liquid phases. This system exhibit partial miscibility, it will exist as single or two phases depending on few variables. In order to know and identify the variable affecting the miscibility, phase rule is used. Upon calculating using phase rule (a rule relating the number of variables upon phases that can exist in equilibrium containing a given number of components), it is identified that the degree of freedom are two as F=2+2-2=2. The two degrees of freedom are temperature and percentage of phenol in water. Thus, only these two variables are required to plot the graph of phenol-water system.

From the graph above, increasing composition of phenol in water will decrease the miscibility of phenol    in water as a higher temperature is required to become single phase. However, once the composition of phenol in water exceeds 37%, the miscibility will be increase in increasing composition of phenol in water as lower temperature is needed to make it appears as single phase.

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

When foreign material is being added to a binary system, it will results in ternary system. We have to know the solubility of the added material. If the added material is soluble only in one component or the solubility of both liquids is different, the mutual solubility (miscibility) of the two liquids component will decrease. These will results in either lowering of the lower consolute temperature or increasing in the upper consolute temperature.

If the added material is soluble in both liquids component, the mutual solubility of (miscibility) of the two liquids components will increase. This will causes the lowering of the upper consolute temperature or the increasing in lower consolute temperature. This process is called blinding.This effect is important as it will help in extraction of material

DISCUSSIONS

In this experiment, we are going to discuss two-component systems containing liquid phases. A very good example of this two-component system is phenol and water. These liquids are partially miscible in each other. 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 only one liquid phase.

            For phenol/water system, it is a two-component system containing liquid phases. Thus, the degrees of freedom are two as F=2-2+2=2. The two degrees of freedom are temperature and percentage of phenol in water in volume. 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 51ºC, 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. From the graph, we notice that the maximum point is at 68.5ºC. This is known as the upper consolute temperature or critical solution which is the maximum temperature at which the two-phase region exists. All combinations of phenol and water above this temperature are completely miscible. A line drawn across the region containing two phases is known as tie line. The tie line 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 known as the conjugated phases. Tie line in a phase diagram use to calculate the composition of each phase and the weight of the phases.

            Certain precautions should be taken to acquire an accurate result. The film should be adhered on the mouth of conical flask by placing the thermometer in the middle of the mouth after the addition of phenol. This is because phenol is a volatile chemical. In addition, we have to be careful when handling phenol due to the acidity and carcinogenic properties of phenol. Pipette is used instead of measuring cylinder on order to obtain more accurate volume required.

CONCLUSIONS

The miscibility of phenol and water are depending on the temperature of the mixture and the composition of phenol in water. The critical solution temperature is at 68.5ºC, above it the mixture appears as single phase. The composition of phenol in which high temperature needed to make the mixture miscible is at 37% of phenol in water.

REFERENCES

Patrick J. Sinko, Lippincott Williams and Wilkins. Martin’s Physical Pharmacy and Pharmaceutical Sciences, 5th Edition.

Alexander T Florence and David Attwood. (2006). Physiocochemical Principles of Pharmacy. 4th Ed. Palgrave. USA.