TITLE :
Phase Diagrams (Part B)
AIM :
To determine the mutual solubility curve for phenol and water
INTRODUCTION :
Factually speaking ,miscibility is the characteristic of liquids to mix in all proportions, forming a homogeneous solution. Water and ethanol are miscible because they mix in all proportions. By contrast, substances are said to be immiscible if in some proportion, they do not form a solution.
Some liquids are soluble with each other in certain proportions. The maximum temperature at which the two-phase region exists is termed the critical solution or upper consolute temperature. In the case of the phenol-water system, the critical solution temperature is 66.80C. Therefore, all mixtures of phenol and water above 66.80C will yield one single phase liquid but mixtures exist as different phases under 66.80C. At equilibrium, it is known as conjugate phases. The composition for the two layers of liquid at equilibrium is constant at any temperature below the critical solution temperature. Relative amounts of the two phases will vary if we are working on a tie line.
Apparatus: Boiling tubes, tongs, test tube holder, thermometer
Material: Phenol, distilled water, water bath
PROCEDURE :
1. Sealed tubes containing amounts of phenol and water to produce a phenol concentration scale from 8% to 80% with total volume is 10 ml are prepared.
2. To increase temperature through heating, the tubes are heated in water bath.
3. The water in the beaker is stirred and if possible, the tubes are shaken as well.
4. The temperature for each of the tube is observed and recorded at which the turbid liquid becomes clear.
5. The tubes are removed from the hot water and the temperature is allowed to reduce gradually.
6. The temperature at which the liquid becomes turbid and two layers are separated is recorded.
7. With that, the average temperature for each tube at which two phases are no longer seen or at which two phases exist is determined.
8. The graph of phenol composition (horizontal axis) in the different mixtures against temperature at complete miscibility is plotted. The critical solution temperature is determined.
RESULT :
Plot the graphs of phenol composition (horizontal axis) in the different mixtures against temperature at complete miscibility. Determine the critical solution temperatures.
DISCUSSION ::
In fact , phase rule which is dedicated by J. William Gibbs relates the effect of the least number of independent variables, particularly temperature, pressure and concentration upon different phases namely solid, liquid and gases in condition that it is at equilibrium containing fixed number of components. The phase rule referring to is expressed as follows:
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. The number of components is the least number of constituents where the composition of every phase in the system at equilibrium can be expressed in the form of chemical equation. Whereas the number of freedom is the smallest number of intensive variables.
However, in this experiment, only temperature is needed to define the system since the pressure is fixed at 1 atm. A series of tubes containing known varying percentage of phenol and water were heated and also cooled. Upon plotting the average temperature for the temperature when the system is homogenous and when two phases exist against the percentage of phenol by weight, a curve in the graph above is obtained. The region inside the curve represents the region where the mixtures will separate into two phases. In the contrary, the region outside the curve represents the percentages of phenol and temperatures where homogenous solution will be obtained.
The curve also dedicates the critical solution temperature or upper consolute temperature which is at 640C. Ideally, the critical solution temperature should be 66.80C. This deviation may arise because of inaccurate temperature readings. The temperature when the phases start to change upon cooling may not been taken in time since the phases changed rapidly. While in some cases, during heating, the temperature increased quite rapidly. Thus, precaution steps must be taken to avoid this error. For example, we should observe the temperature and phases changes from time to time in order to obtain the first temperature when the phases start to change. Besides, the conical flask containing the mixtures of phenol and water might not sealed tightly causing evaporation of phenol. This results in incorrect actual percentage of composition in the mixtures. Furthermore, during measurement of liquid, parallax error probably took place. The mixture should not be shaken when it is cooled to ensure that it is in remain at equilibrium.
REFERENCE :
1. Martin,A.N.2006. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences. 5th Ed. Philadelphia: Lea & Febiger.
2. “IUPAC Compendium of Chemical Terminology". http://www.iupac.org/goldbook/LT07279.pdf. Retrieved 2009-03-05.
3. Alfonso R. Gennaro al.1995. Remington: The Science & Practice of Pharmacy.19th Edition. Easton, Pennsylavania: Mack Publishing Company.
To determine the mutual solubility curve for phenol and water
INTRODUCTION :
Factually speaking ,miscibility is the characteristic of liquids to mix in all proportions, forming a homogeneous solution. Water and ethanol are miscible because they mix in all proportions. By contrast, substances are said to be immiscible if in some proportion, they do not form a solution.
Some liquids are soluble with each other in certain proportions. The maximum temperature at which the two-phase region exists is termed the critical solution or upper consolute temperature. In the case of the phenol-water system, the critical solution temperature is 66.80C. Therefore, all mixtures of phenol and water above 66.80C will yield one single phase liquid but mixtures exist as different phases under 66.80C. At equilibrium, it is known as conjugate phases. The composition for the two layers of liquid at equilibrium is constant at any temperature below the critical solution temperature. Relative amounts of the two phases will vary if we are working on a tie line.
Apparatus: Boiling tubes, tongs, test tube holder, thermometer
Material: Phenol, distilled water, water bath
PROCEDURE :
1. Sealed tubes containing amounts of phenol and water to produce a phenol concentration scale from 8% to 80% with total volume is 10 ml are prepared.
2. To increase temperature through heating, the tubes are heated in water bath.
3. The water in the beaker is stirred and if possible, the tubes are shaken as well.
4. The temperature for each of the tube is observed and recorded at which the turbid liquid becomes clear.
5. The tubes are removed from the hot water and the temperature is allowed to reduce gradually.
6. The temperature at which the liquid becomes turbid and two layers are separated is recorded.
7. With that, the average temperature for each tube at which two phases are no longer seen or at which two phases exist is determined.
8. The graph of phenol composition (horizontal axis) in the different mixtures against temperature at complete miscibility is plotted. The critical solution temperature is determined.
RESULT :
DISCUSSION ::
In fact , phase rule which is dedicated by J. William Gibbs relates the effect of the least number of independent variables, particularly temperature, pressure and concentration upon different phases namely solid, liquid and gases in condition that it is at equilibrium containing fixed number of components. The phase rule referring to is expressed as follows:
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. The number of components is the least number of constituents where the composition of every phase in the system at equilibrium can be expressed in the form of chemical equation. Whereas the number of freedom is the smallest number of intensive variables.
However, in this experiment, only temperature is needed to define the system since the pressure is fixed at 1 atm. A series of tubes containing known varying percentage of phenol and water were heated and also cooled. Upon plotting the average temperature for the temperature when the system is homogenous and when two phases exist against the percentage of phenol by weight, a curve in the graph above is obtained. The region inside the curve represents the region where the mixtures will separate into two phases. In the contrary, the region outside the curve represents the percentages of phenol and temperatures where homogenous solution will be obtained.
The curve also dedicates the critical solution temperature or upper consolute temperature which is at 640C. Ideally, the critical solution temperature should be 66.80C. This deviation may arise because of inaccurate temperature readings. The temperature when the phases start to change upon cooling may not been taken in time since the phases changed rapidly. While in some cases, during heating, the temperature increased quite rapidly. Thus, precaution steps must be taken to avoid this error. For example, we should observe the temperature and phases changes from time to time in order to obtain the first temperature when the phases start to change. Besides, the conical flask containing the mixtures of phenol and water might not sealed tightly causing evaporation of phenol. This results in incorrect actual percentage of composition in the mixtures. Furthermore, during measurement of liquid, parallax error probably took place. The mixture should not be shaken when it is cooled to ensure that it is in remain at equilibrium.
REFERENCE :
1. Martin,A.N.2006. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences. 5th Ed. Philadelphia: Lea & Febiger.
2. “IUPAC Compendium of Chemical Terminology". http://www.iupac.org/goldbook/LT07279.pdf. Retrieved 2009-03-05.
3. Alfonso R. Gennaro al.1995. Remington: The Science & Practice of Pharmacy.19th Edition. Easton, Pennsylavania: Mack Publishing Company.
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