Lab 3: Part B (Mutual Solubility Curve for Phenol and Water)

TITLE: Mutual solubility curve for phenol and water

AIM:

1. To determine the critical solution temperature between phenol and water
2. To determine the solubility of two partially liquids (phenol-water)

MATERIALS & APPARATUS:

Phenol, parafilm, distilled water, 10ml measuring cylinder, 50ml measuring cylinder, test tubes, thermometers, beaker, test tube racks, and test tube holder

PROCEDURE:

1. The volume of phenol and water required  to prepare a phenol concentration with a scale 8% are calculated and prepared inside a test tube.
2. A thermometer is fixed inside the test tube. The mouth of the test tube is then covered with a parafilm.
3. The test tube containing the phenol concentration and a thermometer is heated in a water bath until the turbid liquid becomes clear. The water and the tube are shaken during heating.

   

   Figure 1 shows a one liquid phase

4. The test tube is then removed from the water bath. The temperature is allowed to reduce gradually.

   

   Figure 2 a two liquid phase

5. The temperature at which the liquid becomes turbid and two layers are separated are observed and recorded.
6. The average temperature is determined.
7. Steps 1 to 7 are repeated with phenol concentration scale 30%, 50%, 60% and 80% respectively.

   

   Figure 3 shows for phenol concenration 80%

RESULTS:

Test tube	Phenol		Water		Temperature when turbid liquid becomes clear, °C	Temperature when liquid becomes turbid, °C	Average temperature, °C
	%	ml	%	ml
A	8	1.6	92	18.4	65	-	-
B	30	6.0	70	14.0	72	60	66
C	50	10.0	50	10.0	78	58	68
D	60	12.0	40	8.0	80	42	61
E	80	16.0	20	4.0	67	-	-

DISCUSSIONS:

Phenol-water system is two-component systems containing liquid phases. This system exhibit partial miscibility. The curve shown in the graph above shows the limits of the temperature and concentration within which two liquid phases exist in equilibrium. The region outside the curve shows the system that having one liquid phase.

Since the phase rule is F= C - P+ 2, value F of this system for one liquid phase is three. As the pressure is fixed, it is necessary to fix both temperature and the concentration of one of the liquid. Since the concentration were expressed on a weight-weight basis, the concentration of another liquid can be easily known. For the system of two liquid phases, the value of F is two. Again, as the pressure is fixed, only need to define the temperature to completely define the system.

For instance, at 50ºC, two liquid phases of phenol-water system occur between 11% up to 63% by weight of phenol in water. This was proved from the experiment as the system at which were 8% and 80% by weight of phenol in water, the system did not become turbid after being cooled to room temperature. Easily said, one liquid phase of phenol-water system occur when there is a small quantity of phenol is added to larger amount of water or a large amount of phenol added to smaller amount of water.

Besides, the maximum temperature at which the two liquid phases existed is the critical solution or upper consolute temperature. As from the graph above, the upper consolute temperature is 68ºC. Above 68ºC, phenol and water are completely miscible thus yield one liquid phase.

There were some errors that occurred throughout the experiment that caused some errors in the results. One of the errors was the change in the pressure of the system due to the parafilm was not seal tightly causing phenol to be evaporated. Another error was the exact duration the two liquid phases existed was not accurate.

Therefore, one of the precautions that should be taken to reduce the errors is by ensuring that the mouth of the tube is sealed tightly with parafilm throughout the experiment to avoid changes in the pressure of the system. Furthermore, should be aware when the moment of one liquid phase or two liquid phases occur so that can be recorded immediately.

QUESTIONS:

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

The adding of foreign substances to a system can give effect to the phase separation and critical solution temperature. For phenol-water system, substances such as naphthalene and sodium chloride reduce the miscibility of the two liquids with each other. Naphthalene is soluble in phenol while sodium chloride is soluble in water. The water molecules will associate with ions of sodium chloride and hydrating them. The ions will then lower the tendency of water to solvate phenol. This causes increase in critical solution temperature and higher concentration of phenol on the phenol-rich side of the coexistence curve. In pharmaceutical industry, salt are being added to form a phase separate between organic material and salty aqueous phase.

Besides, addition of foreign substances can also increase the miscibility of the first two liquids. This is known as ‘blending’. For example is the use of propylene glycol as a blending agent that helps in improving the miscibility of volatile oils and water.

CONCLUSION:

The critical solution temperature of phenol-water system is 68ºC. The solubility of two partially liquids, which in this experiment were water and phenol can be determined by referring to the graph of percentage of volume of phenol in water against the average temperature plotted. Outside the curved line, the system would be miscible. While, below the curved line, the system would be immiscible, thus produced two liquid phases.

REFERENCE:

1.   http://www.globalresearchonline.net/journalcontents/Volume3issue2/Article%20012.pdf

2.   Aulton, M.E. & Taylor, K.M.G. 2013. Aulton’s Pharmaceutics: The Design and Manufacture of Medicines. 4^th Edition. Elsevier: Churchill Livingstone.