PRACTICAL 2 : PHASE DIAGRAM

PART B

DATE: 26/03/2013

Objective:  

1)      To investigate the critical solution temperature of water-phenol system.

2)      To determine the mutual solubility curves of phenol and water.

Introduction

Some liquid are miscible in all  proportions, such as ethanol and water. However, some cases, the solubility of one liquid into the other is limited, such as phenol-water are partially miscible under ordinary condition.

However, the miscibility of liquid can be influenced by the temperature of the system. A variation in the proportion of the component can causes the quantities of two layer to change One of the saturated layer is phenol in water while other are water in phenol. Phenol-water will become more soluble with rising temperature until the critical solution temperature is achieved. Critical solution temperature is the temperature at which complete miscibility is reached as the temperature is raised. Above the point, phenol-water are completely miscible. At any temperature below the critical solution temperature, the composition for two layers of liquids in equilibrium state is constant and does not depend on the relative amount of these two phases.

Next, the mutual solubility for a pair of partially miscible liquids in general is also influenced by the presence of a third component. The mutual solubility curves of system can be obtained by analytical method and synthetic method.

Procedure

1. 7 test tube was prepared.

2. The first test tube was filled with 100% water and 0% phenol.

3. Then, phenol was added to the rest of the test tube until sixth test tubes with  concentration scale between 8% to 80%.

4. The seventh test tube was filled with 100% phenol and zero water.

5.  The second until the sixth test tube were covered with perifilm before being heated.

6. Next, the tubes were heated in a beaker containing water.

7. The water was stirred and the tubes were shaken well if possible.

8. The temperature for each of the tube at which the turbid liquid becomes clear was observed and recorded.

9.  The tubes were removed from the hot water and the temperature was allowed to reduce gradually. The temperature at which the liquid becomes turbid and two layers were separated was recorded.

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

11. Part of the tubes were cooled.

Graph of phenol composition (horizontal axis) in the different mixtures against temperature at complete miscibility

Based on the graph, the critical solution temperatures is 65.8 °C.

Discussion

Based on the diagram, the graph shows the temperature against the percentage by weight of phenol in water. The average of the two readings ( that obtained from temperature when solution become clear and the temperature when it’s become cloudy back ) gives the temperature of complete miscibility of the two liquid (water and phenol).The temperature of two liquid phases; phenol in water to become one liquid phase increase as the composition of phenol in water increase until reach the critical temperature.

The critical temperature that we obtained from the result is 65.8˚C. This result are close to the theoretical value that is 66.8˚C. At this temperature, all combinations of phenol and water above this temperature are completely miscible and yield one-phase liquid systems. Applying the phase rule to the diagram, shows that with a two-component condensed system having one liquid phase, so F = 3.  Because the pressure is fixed, F reduces to 2, and it is necessary to fix both temperature and concentration to define the system. Thus, When two liquid phases are present, F = 2 again.

However, there were some precaution step during conducted this experiment. Firstly, we must wear safety goggles and gloves to avoid any contact with a chemical use during the experiment. Next, the water must be stirred gradually during heating to allow the equal amount of heat dispersed throughout the water. Then, our eyes must be perpendicular to the temperature when take the temperature reading to avoid parallex error and ensure the accurate reading.

Question

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

The foreign substances like impurities will affect the critical solution temperature. If the foreign substance is soluble in one of the two liquids, the critical temperature is increases, due to the salting out of water. When the added substance dissolves in both the liquids, the critical solution temperature is lowered because of negative salting out effect. This effect is important to the industrial production of highly concentrated solutions of tar acids (phenols and cresols) used as disinfectants.

CONCLUSION

From the experiment, the mutual solubility of phenol and water can be influenced by the temperature and will affect the critical solution temperature. The critical solution temperature obtained from this experiment is 65.8˚C.

REFERENCE

1. Advanced Practical Physical Chemisty, 29th edition,by Dr. J.B. Yadav, page 120, year  publisher : 2010

2. College Practical Chemistry, by V K Ahluwalia, Sunita Dhingra, page 360 , year 2005

3. Polymer phase diagrams: a textbook, by Ronald Konigsveld, W. H. Stockmayer, E. Nies , page 46, year 2001

4. http://dictionary.babylon.com/partial_miscibility_(partially_miscible)/

5. http://global.britannica.com/EBchecked/topic/444973/partial-miscibility