Practical 3a: Phase Diagrams (Mutual solubility curve for phenol and water)

Aim:

To identify how concentration of phenol and temperature affect miscibility of phenol and water.

Introduction:

Liquids are miscible with each other in all proportions, as example: ethanol and water which is completely miscible. Others have miscibility I limited proportions in other liquids such as ether – water, phenol – water which are only partially miscible.

            Basically, both liquids will become more soluble as the temperature rise until the critical solution temperature or consolute point is attained, and above this point the liquid become completely miscible (single phase is seen). There is a big possibility that any pair of liquids can form a closed system, whereby both upper and lower critical solution temperatures exist, however it is not easy to determine both the temperatures, this is due to solution will evaporates or freezes except for nicotine and water.

            The composition for two layers of liquids 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 mutual solubility for a pair of partially miscible liquids in general is extremely influenced by the presence of a third component.

Procedure:

1)        Tightly sealed test tubes containing amounts of phenol and water with phenol concentration of 8%, 11%, 20%, 35%, 50%, 63%, 70% and 80% are prepared in fume chamber.

2)        The test tubes are heated in water bath to increase the temperature.

3)        The water is stirred and the test tubes are shaken.

4)        The temperature for each of the tube at which the turbid liquid bocomes clear is observed and recorded.

5)        The  test tubes are removed from hot water bath and the temperature are allowed to reduce gradually.

6)        The temperature at which the liquid becomes turbid and two layers are separated is recorded.

7)        Average temperature for each tube at which two phases are no longer seen or at which two phases exist is determined. (Part of the tubes may need to be cooled besides being heated as instrusted above)

Apparatus / Material:

Test tube, Beaker, Thermometer, Water bath, Test tube rack, Test tube holder, Aluminium foil, Parafilm, 1ml pipettle, Measuring cylinder, Dropper

Chemicals:

Pure water, 1.0M Phenol

  

Result:

Test Tube	Percentage by Weight of Phenol/ %
1	8	50.0	-	50.0
2	11	59.0	46.0	52.5
3	20	74.0	69.0	71.5
4	35	77.0	72.0	74.5
5	50	79.0	70.0	74.5
6	63	70.0	60.0	75.0
7	70	65.0	-	65.0
8	80	55.0	-	55.0

Discussion:

            In this experiment we would like to study the effect of phenol concentration (percentage by weight of phenol) and temperature on miscibility of phenol – water solution. Before we started the experiment, we calculated the volume of phenol and water respectively to obtain the accurate concentration that we needed for each solutions.

            During this experiment, the adding of phenol into the water should be done in fume cupboard due to phenol is highly carcinogenic substance and may cause neoplasm if the phenol vapor is inhaled. To ensure the safety, test tube that contain phenol and water mixture should not be bring out from the fume cupboard. The test tubes that contain phenol – water mixture is then wrapped with parafilm and aluminum foil to prevent the escaping of vapor and this may affect the concentration of the solution.

Besides, the heating process should be done in water bath which located in fume cupboard to prevent the vapor from escaping to the surrounding. During the heating process, the temperature that immersed in the test tube should be completely immobilized to prevent stirring that may affect the rate of dissolution of phenol in water.

While taking the temperature, the position of eyes of the reader must be perpendicular to the scale of the thermometer to avoid parallax error that may affect the accuracy of readings. Moreover, observation when the solution turn cloudy must be done by the same student due to different people will have different perspective about the cloudiness of solutions.

Lastly, the each solution should experience heating and cooling process completely before another solution is heated or cooled. For example, do not start to heat the solution in test tube 2 before the solution in test tube 1 is completely cooled down as this may affect the accuracy or even miss to obtain the data.


Conclusion:

The miscibility of phenol and water with different concentration of phenol depends on temperature.

References:

1. Martin’s Physical Pharmacy and Pharmaceutical Sciences, 5^th edition, Patrick J. Sinko, Lippincott Williams and Wilkins
2. Physicochemical Principles of Pharmacy 4^Th edition, Alexander T Florence and David Attwood, Pharmaceutical Press
3. Chemistry: The Study of Matter, Fourth Edition. Prentice Hall.