Practical 3 : Phase Diagrams

PART B

Title  :  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 mutual solubility curve for phenol and waterTo measure the CST (Critical Solution Temperature.

Date of Experiment :  4 November 2014

Introduction

             There are some liquid that are miscible at all different composition, one of the example is: ethanol and water. On the other hand, other liquids,they are partially miscible with one another in limited proportions, for example: ether-water system and phenol-water system. (Even though phenol is not really a liquid, but we consider it as a liquid because as we add in the first part of water, the melting point is reduced until it becomes below room temperature to form a liquid-liquid system.

In general,two liquids will be more miscible when the temperature is increased until it reaches the critical temperature or consolute point of the solution and above this point, the two liquid is miscible at any proportion. 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 (before the substance freezes or evaporates) except for nicotine and water.

            While at any temperature below the critical solution temperature, the composition for two layers of liquid in equilibrium is always a constant and it does not depend on relative amount of the two phases. The mutual solubility for a pair of partially miscible liquids in general is extremely by the presence of a third component.

Material     

   

Phenol

                           

   Distilled Water

Apparatus

               Measuring Cylinder

    Test Tube

 Test Tube Holder

 Thermometer

 Pipette

 

   Water Bath

 Procedure

  1.   8 test tube were prepared with different composition of phenol and water

Test tube	1	2	3	4	5	6	7	8
Water (ml)	1.6	2.2	4.6	7.4	10	12.6	14.4	16
Phenol (ml)	18.4	17.8	15.4	12.6	10	7.4	5.6	4

  2.  All the test tube were tightly seal and each of the tubes were heated in a water bath.Remember to always stir the tubes to allow the solution to mix completely. 

  3.  The solution were heated until the turbid solution turned clear. The temperature was then recorded.

  4.  The test tube was removed from water bath and allowed the temperature to reduce gradually.The temperature at which the turbid solution reformed and two layers are separated was recorded.Some of the test tube might require ice bath for the turbid solution to reform.

   5.  By using the temperature obtained, the average temperature for each tubes at which the two phases were no longer seen or at which two phases were exist were determined.

 6.  A graph of temperature is plotted against different phenol composition in.The critical temperature
is then determined from the graph.

 Result

Concentration of phenol (%)	Volume of phenol (mL)	Volume of water (mL)	Temperature (°C)
			When the liquid turns clear	When mixture turns cloudy	Average Temperature
8.0	1.6	18.4	68.0	31.0	49.5
11.0	2.2	17.8	57.5	51.0	54.4
23.0	4.6	15.4	69.0	66.0	67.5
37.0	7.4	12.6	73.0	65.5	69.3
50.0	10.0	10.0	69.0	66.0	67.5
63.0	12.6	7.4	66.0	59.0	63.0
72.0	14.4	5.6	75.0	41.0	58.0
80.0	16.0	4.0	59.0	35.0	47.0

Question

1.Plots the graph of phenol composition (horizontal axis) in the different mixtures against              temperature at complete miscibility. Determine the critical solution temperature.

Critical solution temperature is the maximum temperature at which the two-phase region exists.Above this temperature,the mixture exist as a single phase layer which is miscible.From this experiment, it is shown in the graph above, the critical solution temperature is approximately 69.3 ˚C which is slightly higher than the theoretical value.

2.Discuss the diagrams with reference to the phase rule.

By applying the phase rule, F=C-P+2 where F is the number of degrees of freedom in the system, C is the number of components and P is the number of phases present. This rule is apply to this two-component condensed system having one liquid phase, F= 2-1+2=3. Because the pressure is fixed, F reduced to 2.Therefore, F=1. From the diagram, if the temperature is given, the composition of the mixture can be determined easily through the diagram. In short, only two independent variables are required to define the phenol and water system completely.

 3.Explain the effect of adding foreign substances and the importance of this effect in pharmaceutical .

Solubility of liquids in liquids is very important in preparation of drug in pharmacy. It is very common for two or more liquids to be mixed together in a pharmacy to make a solution, therefore the pharmacist needs to know what liquids can be mixed together without precipitation occurring.If precipitation occur,it will cause a bad effect to the patient as theor body cannot absorb the drugs into their tissues.

            Addition of foreign material to binary system results in ternary system. If material soluble only in one component, or if solubilities in both liquids are very different, leading to mutual solubility decreased. Its upper consolute temperature is raised and lower consolute temperature is lowered.It will reduces the miscibility of the two liquid and the dispensed medicine may changes its nature and no longer suitable for consumption. Besides, the therapeutic effect of some drug will be reduced and may be harmful to human body.

            However if the addition of foreign material caused it to be soluble in all the components  leading to mutual solubility increased. Its upper consolute temperature is lowered and lower consolute temperature is raised. It is also referred as blending. Thus,it will be more easier for the body to absorb the drugs.

      

Discussion

 Diagram above shows the theoretical phase diagram. As the diagram indicates, at low and high percentages of phenol, water and phenol mix completely, forming a single liquid phase. However, at intermediate compositions (and below the critical temperature) mixtures of phenol and water separate into two liquid phases. Point "h" in the figure is the critical point. Above the critical temperature, phenol and water are completely miscible. This has proven that the phases of the mixture will change in different temperature at different composition.

     Based on the graph above, It is found that above 66.8⁰C,the 2 liquids will become miscible in all proportions because after have been cooled after the heating process,the mixture started to separate into two single layer, and hence it is known as the Critical Solution Temperature (CST).

       - Above this temperature, the liquid mixture is homogeneous which is completely miscible.

       - Below this temperature, the mixture separates into 2 layers which is inmiscible.

This means that in this system, all combinations of water and phenol were completely miscible above 66.8°C.

For the ‘tie line’, it is always parallel to the base line in two component systems. The tie line at equilibrium will separate into phases of constant composition which is called as ‘conjugate phases’.

However,the critical solution temperature is markedly affected by pressure and also by the presence of impurities.So,the pressure and also presence of impurities are controlled during the experiment so that the result won’t be affected.

From our experiment,the result however was slightly different from the theoretical .

From the graph, we determined the critical solution temperature, which is the maximum temperature of two components exists in two different phase region. It shows approximately   69.3 ˚C from the experiment. However, it is slightly varies from the theoretical value which is 66.8 ˚C for phenol-water system.

It may due to errors occur during the experiment. For example, phenol used may contain impurities which then affect its miscibility in water.Pressure of the mixture also cannot be sonstant all the time because of the changing in the surrounding and the handling care. Film must also cover the mouth of test tube firmly to prevent evaporation of phenol. The water bath prepared is make sure not too high temperature to minimise the error during heating of phenol-water in test tube. The temperature is taken immediately once the turbid solution turns clear, however, some of the timing is not accurate which missed out the exact temperature. These factors lead to the deviations of the critical solution temperature in this experiment.

   

Conclusion

In conclusion,the critical solution temperature for our solution is 69.3 ˚C which is the maximum temperature.We also get a better understanding about mutual solubility of phenol-water in different composition and a graph have been plotted to show the overall result.