Experiment 1 Part B: Phase Diagrams – Mutual Solubility curve for phenol and water

Experiment 1

Part B: Phase Diagrams – Mutual Solubility curve for phenol and water

Objectives:

1. To measure the miscibility temperatures of several water-phenol mixtures of known composition.
2. To determine the phase coexistence line (miscibility temperature versus composition) and the critical composition and temperature calculated.
3. To measure the effect of a third component on the water-phenol critical point.

Introduction:

Liquids such as ethanol and water are miscible with each other in all proportions. Other examples such as etherwater, phenol-water (Note that the phenol here is not really liquid, but is considered to be so since the solid’s melting point under room temperature is reduced by the addition of the first part of water in order to produce a liquid-liquid system) have miscibility in limited proportions in other liquids.

As temperature keeps rising, usually both liquids become more soluble until the critical solution temperature or consolute point is attained. The liquids will become completely miscible after reaching above this point. Any pair of liquids can form a closed system, whereby both upper and lower critical solution temperature exist. Both temperatures (before the substance freezes or evaporates) are not easily to determine 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. Also, the presence of a third component will influence the mutual solubility for a pair of partially miscible liquids.

Materials & Apparatus:

8 boiling tubes, beaker, measuring cylinder, pipette, water bath, parafilm sealed thermometer, water and phenol solution.

Procedure:

1. In a tightly sealed tube, certain amount of phenol and water was prepared.

Test tube	1	2	3	4	5	6	7	8
Percentage of phenol (%)	8	11	23	38	50	63	71	80
Volume of phenol (mL)	1.6	2.2	4.6	7.6	10.0	12.6	14.2	16.0
Volume of water (mL)	18.4	17.8	15.4	12.4	10.0	7.4	5.8	4.0

2. Each of the test tubes was heated in a water bath. Remember to always stir the water and shake the tubes as well.
   
3. The temperature for each of the tube at which the turbid liquid becomes clear was observed and recorded.

4.The tube from the hot water bath was removed and allowed for the temperature to reduce gradually. The temperature at which liquid becomes turbid and two layers are separated was recorded.

 

5.The average temperature for each tube at which two phases are no longer seen or at which two phases exist was determined. 

Results:

Test tube	1	2	3	4	5	6	7	8
Percentage of phenol (%)	8	11	23	38	50	63	71	80
Volume of phenol (mL)	1.6	2.2	4.6	7.6	10.0	12.6	14.2	16.0
Volume of water (mL)	18.4	17.8	15.4	12.4	10.0	7.4	5.8	4.0
Temperature at which turbid liquid becomes clear ( ̊ C)	40	52	59	67	63	53	49	34
Temperature at which liquid becomes turbid ( ̊ C)	37	50	61	69	60	50	47	35

FIGURE 1: GRAPH PERCENTAGE OF PHENOL AGAINST TEMPERATURE AT WHICH THE TURBID LIQUID BECOME CLEAR

Discussion:

Miscibility is the property of substances to mix in all proportions, forming a homogeneous solution. The term is most often applied to liquids, but applies also to solids and gases. Water and ethanol, for example, are miscible because they mix in all proportions.

As for phenol and water, phenol is partially miscible with water. Thus, in the graph it shown that, below the curve there are two phase of liquid while the upper region of the curve is for one liquid phase which after the phenol and water is miscible with each other.

Based on the result, temperature which the turbid become clear is the temperature at which the double phase of phenol and water become a single phase of liquid. While for the temperature at which the clear water become turbid is the temperature at which the single phase liquid become a double phase.

The highest temperature stated for the double phase turned to a single phase is 66.8 degree Celsius.

The errors that can be detected in this experiment are the tube is not tightly sealed, thus phenol will evaporate so this will reduce the concentration of phenol in tubes. We also maybe not aware when the solution might become separated in two layers and causes the temperature recorded to be not accurate. Besides, we use measuring cylinder to measure the amount of phenol and water, so it might causes the concentration to be inaccurate.

The precaution that can be taken in this experiment are 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, we use phenol in this experiment, as we know phenol is an acidic and carcinogenic compound, thus extra care should be taken such as wearing a gloves and protective goggle.

Conclusion:

The critical solution temperature for the experiment is 66.8 degree Celcius. The phenol  and water are partially immiscible. The double phase of phenol and water turned into single phase at 66.8 degree Celcius. 

 References:

1. Martin, A.N. 2006. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences. 5^th Ed. Philadelphia: Lea & Febiger.
2. Florence, A.T. & Atwood, D. 2006. Physicochemical Principles of Pharmacy. 4^th Ed. New York: Macmillan.