PRACTICAL 2 : Determine the solubility curve for phenol and water

Title: Phase Diagram

Aim: To determine the solubility curve for phenol and water

Introduction:

                 A few types of liquids are miscible to each other at all measurement, for example: ethanol and water. Other liquids are miscible in other liquids at a limited proportion, for example: ether-water, phenol water. (Here, phenol are is not really liquid, but is considered as like that because addition of first part water decrease the melting point below room temperature to produce a liquids system).

                 In general, both liquids become more soluble with increasing of temperature until reach one critical solution temperature or consolute level and at above this level ,liquids become miscible at all measurement. It is possible that any pair of liquids can form a closed system, in which both critical solution temperature occur at above and below of it, but not easy to determine both of it(before the substance solidified or evaporate) except the nicotine and water.

               At any temperature below a critical solution temperature, the composition for two layer of liquids in equilibrium condition is constant and not depends on comparison amount for both of this phases. In general, the miscibility between a pair of liquids which is partially soluble is so affected by existence of third component.

Results

Percentage of phenol (%)	Volume of phenol (mL)	Volume of water (mL)	Temperature (ºC)			Average temperature (ºC)
			1	2	3
0.0	0.0	20.0	25.0	25.0	25.0	25.0
8.0	1.6	18.4	50.0	56.0	50.0	52.0
11.0	2.2	17.8	58.0	64.0	56.0	59.3
37.0	7.4	12.6	68.0	68.0	68.0	68.0
63.0	12.6	7.4	64.0	63.5	57.0	61.5

Discussion

In this experiment, two-component systems containing liquid phases are discussed here. Phenol is partial miscible with water. 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.

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 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 in this experiment. First, after the addition of phenol into the conical flask, the top of conical flask should be wrap with the film 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.

In conclusion, phase diagram is used in practice to formulate systems containing more than one component where it may be advantageous to achieve a single liquid phase product.

Conclusion

The consulate temperature for phenol/water system is 68.5ºC. Phenol is partial miscible with water and at certain temperature and certain concentration, one liquid phase will obtain.

References

1. E. A. Moelwyn-Hughes. (1961). Physical Chemistry, 2^nd Ed. Pergamon. New York.