Thursday, December 15, 2016

Lab 3: Part A (Determination of Phase Diagram for Ethanol/Toluene/Water)



TITLE: Determination of phase diagram for ethanol/toluene/water system.

AIM: To determine the phase diagram for ethanol/toluene/water system.

APPARATUS: retort stand and clamp, burette, pipette, conical flask,measuring cylinder

dropper

conical flask

measuring cylinder



CHEMICALS: ethanol, toluene, distilled water.
ethanol

toluene

INTRODUCTION:
            A phase diagram is a graph that shows under what conditions distinct phases of matter occur and it is to elaborate about a phase or state. The major features of a phase diagram is the triple point and phase boundaries. The phase rule is a device to relate the effect of the least number of independent variables upon the various phases that can exist in an equilibrium system containing given number of components. Phase rule is expressed as:
F=C – P + 2
F=number of degrees of freedom
C=number of components
P=number of phases


           A three component system is one with three components such as mixture of three liquids or a solid in two liquids. In systems containing three components but only one phase, F=4 where the four degrees of freedoms are temperature, pressure and the concentrations of two of the three components. For three components systems at constant temperature and pressure, the compositions may be stated using triangular coordinate graph paper.
Based on the figure above, each point A, B and C each represents pure components in 100%. Each side of the triangle represents the two-component mixtures and within the triangle, it represents the ternary components. Furthermore, any lines that is parallel to the side of the triangle is a percentage value for the component. At point K, the line intercepts that shows it has 20% A, 50% of B and 30% of C. The sum of all distances from K is of the line that is drawn parallel to the sides of the triangle is same and equals to the length of any side of the triangle.
            An addition of a third component to a pair of miscible liquids can change the two components’ mutual solubility. If the third component is soluble in one of the tow components, the mutual solubility of the liquid pair is decreased. Nevertheless, if the third component is soluble in both of the liquids, the mutual solubility is increased. In an example of mixture of benzene and water, when ethanol is added, the mutual solubility of the liquid pair increased until it reaches a point where the mixture becomes homogenous since ethanol is miscible in both benzene and water. This method had been used in the formulation of solutions between castor oil, alcohol and water including between peppermint oil propylene glycol and water.
            There are many benefits of preparing an oily substance as homogenous water in liquid. The understanding of the triangular phase diagram can help explain what will happen to the system when it is diluted.

PROCEDURES:
  1.  Mixtures of ethanol and toluene are prepared in sealed containers measuring 100cm3 which according to percentages of ethanol (in percent: 10, 25, 35, 50, 65, 75, 90, 95)
  2. 20ml of each mixture are prepared by filling a certain volume using a burette.
  3. Each mixture is filtrated with distilled water until cloudiness is observed which indicates the existence of second phase.
    cloudiness appeared after the addition of distilled water
  4. A little of water is added and then shaken well after the addition into mixtures.
  5. The room temperature is measured.
  6. The percentages are calculated based on the volume of the each component when the second phase starts to appear.
  7. The points are plotted onto triangular paper to give a triple phase diagram at the recorded temperature.
  8. Each determination in this experiment is repeated again to obtain an accurate result. 

RESULTS:
















Test Tube
Ethanol in
Ethanol
Toluene
Distilled water
Total Volume


percentage
Volume of
% of ethanol
Volume of
% of toluene
Average of
% of water
(ml)


(%)
ethanol(ml)
after titration
toluene(ml)
after titration
water added
added



A
10
2
9.3
18
83.9
1.45
6.8
21.45


B
25
5
22.8
15
68.5
1.9
8.7
21.90


C
35
7
33.4
13
62.1
0.95
4.5
20.95


D
50
10
46.1
10
46.1
1.7
7.8
21.70


E
65
13
58.0
7
31.3
2.4
10.7
22.40


F
75
15
60.9
5
20.3
4.7
18.9
24.70


G
90
18
60.6
2
6.7
9.7
32.7
29.70


H
95
19
52.9
1
2.8
15.9
44.3
35.90












the triangular phase diagram of ethanol/water/toluene

DISCUSSION:
The experiment is conducted to determine the phase diagram of ethanol/toluene/water system. Toluene is miscible in ethanol but immiscible in water. But all these three component can be miscible if mixed until certain portion. This experiment is carried out by first mixing the ethanol and toluene which is completely miscible in a conical flask. Then water is titrated into the mixture which is at first will formed in two phase but, as we continue add water into the mixture until reach appropriate amount it will exist in one phase.
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 below the graph shows two phase system, while the region above the graph shows homogenous mixture.
According to phase rule: P + F = C + 2,  Where P is the number of phases in the system
C is the minimum number of chemical components required to constitute all the phases in the system F is the number of degrees of freedom in the system (also referred to as the variance of the’ system).
For ethanol/toluene/water system, we have 3 components and 1 liquid phase. F= 3-1+2= 4. Hence, 4 degrees of freedom are required. They are temperature, pressure, and the concentrations of two of the three components. Only concentrations of two components are required because concentration of the third component can be obtained by further calculation. The experiment was carried out at a constant temperature and pressure. The temperature when this experiment is carried out is 27°C.
Based on the result obtained, when the percentage of ethanol is high and the percentage of toluene is low, more water is needed to observe the cloudiness of the mixture. The cloudiness of the mixture indicates the two phase system. This proved that the ethanol had increased the miscibility of the other two components and more water is needed to break the homogeneity.
There are some errors occur during the experiment is conducted. Firstly, the apparatus is not clean and dry. If the apparatus is not dry, it may affect the result obtained as the water react with mixture of toluene and ethanol. Next, parallax error which may occur when the reading of the buret is taken. Finally, the titration is done by different person so, the observation of the cloudiness might be different.
The precaution steps that must be taken are make sure the apparatus is clean and dry before use it. Next, make sure the level of eye is perpendicular to the reading scale of the apparatus in order to avoid the parallax error. Finally, the titration process should be conducted by one person only to make sure the observation of the cloudiness is the same for all titration. 

QUESTIONS:

1) Does the mixture containing 70% ethanol, 20% water and 10% toluene (volume) appear clear or does it form two layers?
The mixture of these solutions would appear as one phase since ethanol is majority in percentage where ethanol can dissolve in both water and toluene.  As the result, clear solution is obtained.

2) What will happen if you dilute 1 part of the mixture with 4 parts of…?
a)  Water
b) Toluene
c) Ethanol



a) 1 part of mixture with 4 parts of water.
Based on the phase diagram, a clear solution is obtained since the percentage of mixture is outside the bimodal ternary curve.


b) 1 part of mixture with 4 parts of toluene

A cloudy solution would be obtained which mean that the solution appear have 2 phase since the percentage of the mixture is within the bimodal ternary curve.


c) 1 part of mixture and 4 parts of ethanol


Based on the phase diagram, a single phase solution would be obtained since the percentage of the mixture is located outside of bimodal ternary curve. A clear solution is obtained.

CONCLUSION:
            Water, toluene and ethanol is ternary system and ethanol which acts as the other component added to the liquid pair is soluble in both water and toluene. Toluene is immiscible in water and as ethanol is miscible in both water and toluene thus it helps to increase the mutual solubility between water and toluene. From the graph, the area bounded shows a two-phase system and the area that are not bounded or above the graph shows that a homogeneous mixture.
REFERENCE:
  1. Alfred.N Martin. 2006. Martin’s Physical Pharmacy and Pharmaceutical Sciences: Physical Chemical and Biopharmaceutical principles in the Pharmaceutical Sciences. Patrick J. Sinko, Yashveer Singh, David B. Troy. 6th Edition. Maryland: Lippincott William & Wilkins.
  2. Boundless. “Major Features of a Phase Diagram.” Boundless Chemistry Boundless, 26 May. 2016. Retrieved 12 Dec. 2016 from https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/liquids-and-solids-11/phase-diagrams-91/major-features-of-a-phase-diagram-395-1266/

No comments:

Post a Comment