Practical 2 - Phase Diagrams B

Aim/Objective

    1.      To understand the system containing two components by using curve.

    2.      To determine the upper critical solution temperature shown by the system containing water and phenol.

Introduction

The mutual solubility of water and phenol is observed throughout this experiment. When both liquids are heated, results obtained can be explained in the curve. Area inside the curve shows the region where phenol and water mixtures will form two separate layers. The region outside the curve indicates that phenol and water exist in homogeneous solution, where no two separate layers can be seen. Phenol is dissolved in water at different temperature. Both liquids become soluble as the temperature increases until the critical solution temperature is reached. The critical solution temperature here is defined as the maximum temperature at where phenol and water can show two separate layers. Both phenol and water become completely miscible in all proportions at a point called upper critical solution temperature.

The relative masses of two layers are explained by the lever rule as :

 Materials

1.  Phenol

2.  Water

Apparatus

Beakers, tubes, thermometer, electrical heater.

Procedures

1.      The tightly sealed tubes containing amounts of phenol and water were been done to produce a phenol concentration scale between 8% to 80%.

2.      The tubes were heated in a beaker containing water to increase the temperature.

3.      The water was stirred and shaken as well.

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

5.      The test tubes were removed from the hot water and were allowed for the temperature to reduce gradually.

6.      The temperature was recorded at which the liquid becomes turbid and two layers are separated.

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

8.      The graphs of phenol composition in the different mixtures against temperature at complete miscibility were plotted.

9.      The critical solution temperatures were determined.

Results

Percentage of Phenol (%)	Temperature (0C)		Average Temperature (0C)
	Heating	Cooling
8	57	37	47
11	63	46	55
20	70	60	65
50	82	56	69
63	67	48	58
70	62	46	54
80	58	42	50

Graph shown above is plotted based on the results obtained in this experiment.

Temperature-composition diagram for the system consisting of water and phenol.

Discussions

Based on the graph above, temperature fixed at 50 ⁰C. At Point a, system containing 100% pure water. Addition of known increments of phenol to a fixed weight of water will result in the formation of a single liquid phase until the point b is reached. Point b, appears a second phase. The concentration is 11 % by weight of phenol in water. Analysis of the second phase, which separates out on top, shows it to contain 63 % by weight of phenol in water. easing quantities of phenol, for instance, as we proceed across the diagram from point b to point c, systems in which the amount of the phenol-rich phase (B) continually increases at the same time the amount of the water-rich phase (A) decreases. Once the total concentration of phenol exceeds 63 % at 50⁰C a single phenol-rich liquid phase is formed.

Tie line is always parallel to the base line in two component systems. All systems prepared on a tie line at 50° C will separate into phases of constant composition whose composition is b and c. These phases are termed conjugate phases. All combinations of phenol and water above this temperature are completely miscible and yield one- phase liquid systems.

Even small concentrations of salts may have large affects on phase separation and the critical temperature. In aqueous solutions of organic molecules or polymers, salt may be added to make the organic material form a phase separate from the salty aqueous phase. This procedure may be familiar as "salting out." The miscibility of phenol and water is reduced by addition of many common salts such as alkali and alkaline-earth halides.2,3 The origin of the effect is the tendency of water molecules to associate with ions, hydrating them. In that way, simple ions reduce the tendency of water to solvate phenol. The result of adding salt is often an increased critical temperature and greater phenol on the phenol-rich side of the coexistence curve.

Conclusion

The critical solution temperature (upper consolute temperature) is the maximum temperature at which two phase region exists. In the case of the phenol-water system, this is 66.8° Celsius.

References

1. Textbook of Physical Chemistry, A. S. Negi, S. C. Anand, Page : 372-373

http://books.google.com.my/books?id=wyP_V3X8YOIC&pg=PA373&lpg=PA373&dq=mutual+solubility+curve+for+phenol+and+water&source=bl&ots=7x0sSYd-04&sig=FZ4azSIJIs39W-xsMt88lmj7tN8&hl=en&sa=X&ei=s0ObUcyxBY3qrQe7vYHQAg&sqi=2&ved=0CDYQ6AEwAg#v=onepage&q=mutual%20solubility%20curve%20for%20phenol%20and%20water&f=false

2.  Patrick J. S, Martin’s Physical Pharmacy and Pharmaceutical Sciences, 50^th Edition, 2011, Lippincott Williams & Wilkins

Practical 1 - Phase Diagram A

Aim/Objective

                 1.      To understand the system that involves three components.

                 2.      To identify how solubility gets affected by addition of third component.
           3.      To learn the rules relating to triangular diagrams.

Introduction

In a three-component system, the concentration of the component can be represented in the coordinate form. The degree of freedom defined in the system is four which include temperature, pressure and the concentration of two of the three components. The concentration of the third component can be obtained by subtracting the sum of the two of the three components from the total concentration of the system. When discussing on the three-component system, the concentrations of the components are expressed according to the weight basis. When a new component is added to a system containing two components which are miscible, the solubility of the system will be affected. If the third component is more soluble in either one of the two components, the solubility of the system will decrease. The solubility will only increase if the third component added is soluble in both components at the same time.

Rules Relating to Triangular Diagrams

1.      100% by weight of one component is represented by each of the three apexes of the triangle. The same apex will express the 0% of the other two components.

2.      Lines AB, BC and CA show the combinations of two-component mixtures of A and B, B and C, and C and A, respectively.

3.      All possible combinations of A, B and C are represented by the area within the triangle.

4.      If a line is drawn through any apex to a point on the opposite side, the two components represented by points on such a line are said to be in constant ratio.

5.      If a line is drawn parallel to one side of the triangle, it is said that the proportion of one component is constant whereas the other two components vary in concentrations.

  

Apparatus and Materials

·         Burette

·         Beaker

·         Measuring cylinder

·         Retort stand and clamp

·         Toluene

·         Ethanol

·         Distilled water

Procedure

1.      Mixures of ethanol and toluene containing the following percentages of ethanol (in percent) : 10, 25, 35, 50, 65, 75, 90 and 95 were prepared in sealed containers measuring 100 cm³.

2.      20 ml of each mixture was prepared by filling a certain volume using a burette (accurately).

3.      Each mixture was titrated with water until cloudiness is observed due to the existence of a second phase.

4.      A little water was added and the mixture was shaken well after each addition.

5.      The experiment was repeated. Average values were determined.

6.      The room temperature was measured. The percentage was calculated based on the volume of each component when the second phase starts to appear/separate.

7.      The points were plotted onto a triangular paper to give a triple phase diagram at the recorded temperature. 

Result

Ethanol (mL)	2	5	7	10	13	15	18	19
Toluene (mL)	18	15	13	10	7	5	2	1
Average Water (mL)	0.4	0.6	1.0	1.7	3.3	4.7	11.4	22.2

Ethanol (%)	10	24	33	46	57	61	58	45
Toluene (%)	88	73	62	46	30	20	6	2
Average Water (%)	2	3	5	8	13	19	36	53

Diagram 1

Discussion

            In this experiment, we are going to discuss on the properties of the system containing three-component that exist in one phase only.

                                    F = C - P + 2

                                    F = 3 - 1 + 2 = 4

where ;

            F - Degrees of freedom

            C- The number of components

            P - The number of phases present      

The four degrees of freedom are temperature, pressure, and the concentrations of two of the three components. The three components used are Ethanol, Toluene and water. A three-component system can be explained by referring to the phase diagram as plotted in Figure 1. This system occurs at constant temperature and pressure. The compositions of the components are expressed in the form of coordinate for a triangular-diagram.

            Based on the diagram, each of the corners or apexes of the triangle represents 100% by weight of  component ( A=Ethanol, B= Toluene, C= Water). The same apex will represents 0% of the other two components. ( A= 0% of Toluene and Water, B= 0% of Ethanol and Water, C= 0% of Ethanol and Toluene).  

            As we move along Ethanol-Toluene in the direction of  Toluene, the systems of  Ethanol and Toluene containing increasing concentrations of  Toluene and corresponding smaller amounts of Ethanol. Moving along Toluene-Water towards Water will represent systems of Toluene and Water containing more concentrations of Water and closer the closer approached Ethanol on the line Water-Ethanol, the greater will be the concentration of Ethanol in system of  Ethanol and Water.

            The area within the triangle represents all the possible combination of Ethanol, Toluene and Water to give three-component systems. At points M, its represents  the system contain 10% of Ethanol, 88% of Toluene and 2% of water.  The another point R represents 61% of Ethanol, 20% of Toluene and 19% of water. Any line that parallel to one side of the triangle represents ternary systems in which the proportion of one component is constant.

            There are some error while doing this experiment. Generally, there are two kind of errors that usually been done during experiment which are random errors and systemic errors. The common error is the parallax error. The eye is not put perpendicular to the miniscus of the liquid correctly. The temperature during experiment is not constant.

            The precaution steps that should be taken during the experiment are wear safety goggles, glove and lab coat while conducting the chemical. The safety glasses of goggles will protect anything from entering eyes. The lab coat is important to avoid spilling anything on clothes. The glove can protect our hand from chemical that can cause harm. Avoid parallax error by placing the eye such that the line of view is perpendicular to the scale read. The temperature while doing the experiment should be constant.

Practice

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

The mixture will appear clear which is contain one liquid phase and only one layer will be formed.

2. What will happen if you dilute 1 part of the mixture with 4 parts of (a) water (b) toluene (c) ethanol?

a) Two phases will form

b) Two phases will form

c) One phase will form

Conclusion

1.      A three-component system can be explained using a triangular diagram.

2.      The addition of the third component will affect the solubility of the system. The solubility of the system will depend on the solubility of the third component in the other two components.

3.      There are several rules applied when discussing about the triangular diagrams.

References

1.  Patrick J. S, Martin’s Physical Pharmacy and Pharmaceutical Sciences, 50^th Edition, 2011, Lippincott Williams & Wilkins

2.  http://www.csun.edu/~jeloranta/CHEM355L/experiment5.pdf

3. http://www.brocku.ca/earthsciences/people/gfinn/petrology/ternary1.htm