Experiment 1 : Phase Diagrams (Part A) ; Determination of Phase Diagram for Ethanol/ Toluene/ Water System Theory

Date

9 March 2013

Title
Determination of Phase Diagram for Ethanol/ Toluene/ Water System Theory

Objectives

1. Determination of the solubility limits in a ternary system of water and two other liquids (ethanol and toluene), one of which is completely miscible (ethanol) and the other is partly miscible with water (toluene).
2. Construction of the solubility curve of the system being studied on triangular diagram.

Introduction

         In making pharmaceutical formulation. often multiple component need to be mixed together and need to be in homogeneous form. This is usually possible by knowing the exact ratio of each component to be mixed with regard of some other condition such as temperature. In this experiment, there are three components of concern which were Ethanol, Toluene and Water. Water is insoluble and toluene, but as it were mixed together with ethanol, all three components can achieve homogeneous solution at equilibrium if proper proportion was used.

     Often to present a three component system, aid of ternary diagram is needed. Each side of a triangular diagram correspond one of the three component in the system and can be divided into part to produce equilateral grids as shown above. Thus any point in the diagram will show the amount of all three components while a point on the sides will show amount of any two components with each apex represent an amount of 100% of any one of the three components. 

   Following the basis of describing the effect of intensive variable to various phase in a system at equilibrium, which is the phase rule, it is determine that this system have 4 degress of freedom. The four degrees of freedom are - temperature, pressure, and any two from the three component concentration. 

F = C – P + 2

F = 3 – 1 + 2

F = 4

Apparatus and Materials

1. Eight 100cm³ conical flask.
2. Burette
3. Toluene
4. Ethanol
5. Distilled water

Procedures

     An amount of eight, 20 ml solution of toluene and ethanol were prepared in eight different 100cm³  conical flasks. Each flash were filled so that it contain 10%, 25%, 35%, 50%, 65%, 75%, 90% and 95% of ethanol with the rest was toluene. The conical flask were labelled A, B, C, D, E, F, G and H respectively. Measuring these component were done by using a burette to make sure accuracy.

Using a burette to measure and also to do titration.

     Each flask were then were titrated slowly with water and stop when cloudiness were observed which stated that second phase started to appear. The temperature was recorded as well. The data obtained were used to plot onto the triangular diagram. This experiment was not repeated since there was not enough time. Comparison can be done by using other groups data.

Results

• Table of Data

• Data presented in triangular diagram.

Practice

1. Does the mixture containing 70% ethanol, 20% water and 10% toluene (volume) appear clear or does it form two layers?

          It appears in clear solution.

    2.   What will happen if you dilute 1 part of the mixture with 4 parts              of 

           a. water      : Two phase is formed
           b. toluene   : Two phase is formed
           c. ethanol    : The phase remains clear

Discussion

Toluene is soluble in ethanol while it is not soluble with water. But, as these three component were mixed until certain proportion, all three components would be completely miscible. This experiment is carried out by first making a solution of ethanol and toluene which will be completely miscible and addition of water where at first it will make up two phase. As we continue to add more water until appropriate amount, it will result to one phase system.  

Addition of water to the mixture of ethanol and toluene increases the mutual solubility of the liquid pair until at one point the mixture become homogenous. The region under the graph shows that there are two phase system form which consist of water and toluene since the solubility of water with toluene is weaker than that with ethanol. Meanwhile the region above the graph shows homogenous mixture. 

But the result obtained were not to the most accuracy as when the data have been plotted it should have look something like below  graph.

A nice and complete binomial curve

The line which separate the single-phase system and the two-phase system were the point at which supposed to be obtained through this experiment. There are some errors that were formed when conducting this experiment which lead to this inaccuracy which include :

• Exact point when to stop water titration is wrongly determine as the cloudiness disappearance were not properly observed.
• Different rate of agitation may influence the disappearance of cloudiness.

In order to get a better result in doing this experiment is by taking serious consideration to some precaution step. The precaution steps are :

• Rinse the glassware before use to remove impurities as the impurities may affect the result.
• Take the reading of solution with the eye is perpendicular to the meniscus to avoid parallax error.
• Use consistent rate of agitation for each mixture.

Conclusion

The the solubility limits in a ternary system of water and two other liquids (ethanol and toluene) cannot be exactly obtained due to incomplete binomial curve.

References

1. http://www.lboro.ac.uk/research/phys-geog/tri-plot/
2. Website : "Ternary Phase Diagram" (http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/experimental/ternary2.html)
3. http://www.brocku.ca/earthsciences/people/gfinn/petrology/ternary4.htm
4. Martin's Physical Pharmacy and Pharmacautical Science, Sixth Edition, Patrick J. Sinko, Wolters Kluwer, Lippincott Williams & Wilkins.