PRACTICAL 3A: Phase Diagrams: Determination of Phase Diagram for Ethanol/Toluene/Water System Theory; Three Component Systems
DATE: 2nd November 2015
OBJECTIVES:
1.
To determine the phase diagram for
ethanol, toluene and water system.
2.
To determine the solubility limits of
water and the two other liquids which are ethanol and toluene, one of which is
completely miscible (ethanol) and the other one is partly miscible with water
(toluene).
3.
To construct the solubility curve of the
system being studied on triangular diagram.
4.
To know the mutual solubility of liquids
in a two-phase system by using the triangular coordinates.
INTRODUCTION:
A
ternary plot, ternary graph, triangle plot, simplex plot, or de Finetti diagram
is a barycentric plot on three variables which sum to a constant. It
graphically depicts the ratios of the three variables as positions in an
equilateral triangle. Ternary components are represented within the triangular
diagram. Any line parallel to a side of the triangular diagram shows constant
percentage value for a component. The
concentration of each species is 100% (pure phase) in each corner of the
triangle and 0% at the line opposite it. The percentage of a specific species
decreases linearly with increasing distance from EACH corners.
In
the diagram above, each corner are the pure component. While, each side
represents two component mixtures. Any parallel line to a side of the triangle
diagram shows constant percentage value for a component. When the line DE which
is 20% of A intersect with the line FG which is 50% of B would make an
intersection point at K which contained 20% of A, 50% of B and 30% of C.
Their mutual solubility can be changed when there is an
addition of the third component to a pair of miscible liquids. If the third
component is more soluble in one of the two different components the mutual
solubility of the liquid pair is decreased. But, if it is soluble in both of
the liquids, the mutual solubility is increased. However, what will happen to a
system like this when it is diluted should also be known and this can be
explained through the understanding of the triangular phase diagram.
Using a ternary plot for depicting compositions has the
benefit of that the three variables can be conveniently plotted in two dimensional
graph. Using this plot also can create phase diagram by outlining the
composition regions on the plot where phases exists. Different composition of
the three components are representing on different points on the ternary plot.
There are three common methods that can be used to determine the ratios of the
three species in the composition. Firstly is the method of estimation based
upon the phase diagram grid which is this ternary plotting. Secondly, the methods
is for the phase diagrams that do not possess grid lines, the easiest way to
determine the composition is to set the altitude of the triangle to 100% and
determine the shortest distances from the point of interest to each of the
three sides. Last but not least is the method that is based upon a larger
number of measurements, but does not require the drawing of perpendicular
lines.
EXPERIMENTAL METHODS:
Apparatus:
Balance, weighing board,
burette, pipette, conical flask, conical flask stopper, retort stand and clamp,
dropper, aluminium foil, filter funnel.
Chemical:
Ethanol, toluene and
distilled water.
Experimental
Procedures:
1. Mixtures of ethanol and toluene are prepared in
sealed containers containing percentages of 10%, 25%, 35%, 50%, 65%, 75% and
90% of ethanol.
2. 20mL of mixtures that contained 10% of ethanol
are pipetted into a conical flask.
3. The mixture is then titrated with distilled
water until cloudiness observed.
4. The solution is shaken well.
5. The volume of distilled water used is measured
and recorded.
6. Step 2 to step 5 are repeated by using 20mL of 25%,
35%, 50%, 65%, 75% and 90% of ethanol.
7. The percentage based on the volume of each when
the second phase appeared are calculated.
8. Points are plotted on the triangle paper to give
a triple phase diagram at the recorded temperature.
RESULTS AND CALCULATIONS:
Before titration
|
||||
Conical flask
|
Ethanol
|
Toluene
|
||
%
|
mL
|
%
|
mL
|
|
A
|
10
|
2
|
90
|
18
|
B
|
25
|
5
|
75
|
15
|
C
|
35
|
7
|
65
|
13
|
D
|
50
|
10
|
50
|
10
|
E
|
65
|
13
|
35
|
7
|
F
|
75
|
15
|
25
|
5
|
G
|
90
|
18
|
10
|
2
|
H
|
95
|
19
|
5
|
1
|
After titration
|
Total volume of mixed solution (mL)
|
||||||
Conical flask
|
Ethanol
|
Toluene
|
Water
|
||||
%
|
mL
|
%
|
mL
|
%
|
mL
|
||
A
|
9.7
|
2
|
87.4
|
18
|
2.9
|
0.60
|
20.60
|
B
|
24.2
|
5
|
72.5
|
15
|
3.4
|
0.70
|
20.70
|
C
|
33.2
|
7
|
61.6
|
13
|
5.2
|
1.10
|
21.10
|
D
|
44.4
|
10
|
44.4
|
10
|
11.1
|
2.50
|
22.50
|
E
|
56.5
|
13
|
30.4
|
7
|
13.4
|
3.00
|
23.00
|
F
|
61.3
|
15
|
20.4
|
5
|
17.5
|
4.45
|
24.45
|
G
|
57.8
|
18
|
6.4
|
2
|
35.8
|
11.15
|
31.15
|
H
|
50.1
|
19
|
2.6
|
1
|
47.2
|
17.90
|
37.90
|
QUESTIONS:
1.
Does the mixture containing 70% ethanol,
20% water and 10% toluene in volume appear clear or does it form two layers?
The
mixture appear clear when the mixture are composed of 70% ethanol, 20% water
and 10% toluene in volume.
2.
What will happen if you dilute 1 part of
the mixture with 4 parts of water, toluene and ethanol?
When
1 part of the mixture is mixed with water or with toluene, two phased-layer are
formed or in the other word the mixture is immiscible but 1 one part of the
mixture is mixed with ethanol, only one phased-layer is formed which means that
the mixture is miscible.
DICUSSION:
A ternary phase diagram is a
triangular diagram that shows the phase behaviour of mixture containing three
components. By applying the phase rule F = C–P+2 for this experiment, the
degrees of freedom in this system is F = 3–1+2 = 4. Degree of freedom of a
system is the number of independent variables that does not change the number
of phases present at equilibrium. Four degrees of freedom of this experiment
are temperature, pressure, and the concentrations of two components, in which
the temperature and pressure of the system are constant.
Ethanol acts as surfactant and
it causes the water-toluene system become partially miscible. Only a single
phase is formed after ethanol is added because all the liquid are miscible.
Normal water-toluene system is a two-phase system formed which includes
water-rich phase and toluene-rich phase. Water and toluene do not mix
thoroughly Toluene is insoluble in water because it is aromatic hydrocarbon
that is a non-polar molecule. As the volume of ethanol becomes higher, more
volume of water is added to the mixture until cloudiness is observed. This
indicates that ethanol increases the miscibility of the water-toluene system
and therefore it breaks the homogeneity easily.
Based on the ternary phase
diagram plotted, the binomial curve drawn separates the single-phase region and
two-phase region. Region bounded by the curve represents two-phase region while
region unbound by the curve indicates single-phase region. The region above the
curve is region for high ethanol concentration and low toluene concentration.
This indicates that solution mixtures that have higher ethanol concentration
are more miscible, thus it forms homogenous solution that has only a
single-phase solution. For the region below the curve which has lower ethanol
concentration, the solution mixtures are less miscible form two-phase
solution.
The curve plotted is nearly
perfect except at the intersection point 4. At the intersection point 4, the
toluene and ethanol used for experiment are at the same ratio. Different
intersection point represents different concentration of the liquids. The total
percentage of three components involved in this system adds up to 100% at any
intersection point. However, at some intersection point, the total percentage
of components in this system is not 100% as the rounding off changes the
accurate number. The inaccuracy of phase diagram plotted is due to some errors
that occurred during experiment.
These
are the possible errors that affect the accuracy of data. Parallax error occurs
when eyes level of observer is not perpendicular to the reading. Impurities
that remain in the apparatus can affect the concentration of liquids. Since
ethanol and toluene are volatile, some volume may escape from the solution and
this reduces the actual volume of solution. This directly affects the
concentration of liquid and volume of water needed for titration.
Precautionary
steps for this experiment include placing eyes of observer at perpendicular
level to the meniscus of liquids. The apparatus must be rinsed properly before
using to prevent the presence of impurities. Solution must be mixed well. The
conical flask that contains ethanol and toluene should always keep closed as
these liquids are easily escaped to the surrounding.
CONCLUSION:
Water,
toluene and ethanol are one of the ternary system that is the phase diagram
represented in the form of triangle. Although at first toluene and water form
partially miscible liquid and two phase system, single phase was formed after
ethanol was added. This is because ethanol acted as a surfactant which
increases the miscibility of the water-toluene system and turns it into a
single phase system. The higher the concentration of ethanol, the more miscible
the mixtures are and this forms homogenous solution consisting single phase
solution. Lastly,
the errors made in this experiment should be avoided in the future in order to
obtain an accurate result.
PRACTICAL 3B:
DATE:
2nd
November 2015
OBJECTIVES:
1.
To measure the miscibility temperatures of
several water-phenol mixtures of nown composition.
2.
To construct the mutual solubility curve
of a pair of partially miscible liquids, which are phenol and water.
3.
To
determine the critical solution temperature of water-phenol mixtures.
INTRODUCTION:
Ethanol
and water are miscible with each other in all proportions. However, both liquid
can become soluble with the rising of temperature until the critical solution
temperature is achieved and above this point the liquids become completely
miscible. There is a big possibility that any pair of liquids can form a closed
system, whereby both upper and lower critical solution temperatures exist. But
it is difficult to determine both the temperatures except for nicotine and
water.
At any temperature below the
critical solution temperature, the composition for the two layers of liquids in
equilibrium state is constant and does not depend on the relative amount of
these two phases. The mutual solubility for a pair of partially miscible
liquids in general is extremely influenced by the pressence of third component.
Figure 1 Temperature –
composition diagram for the system consisting of water and phenol. (from A. N.
Campbell and A. J. R. Campbell, J. Am. Chem. Soc. 59, 2481, 1937).
The
curve GBHCI shows the limits of the temperature and concentration within which
two liquid phases exist in equilibrium. The region outside this curve contains
systems having but one liquid phase. Starting at the point a, equivalent to a
system containing 100% water (pure water) at 500C, the addition of
known increments of phenol to a fixed weight of water, the whole being
maintained at 50 0C will result in the formation of a single liquid
phase until the point b is reached, at which a minute amount of a second phase
appears. The concentration of phenol and water at which this occurs is 11% by
weight of phenol in water. Analysis of the second phase, which separates out on
the bottom, shows it to contain 63% by weight of phenol in water. This
phenol-rich phase is denoted by the point c on the phase diagram.
As we prepare mixtures containing increasing
quantities of phenol, that is, as we proceed across the diagram from point b to
point c, we form systems in which the amount of the phenol-rich phase (B)
continually increases, as denoted by the test tubes drawn in Figure 2.14. 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. The maximum temperature at which the two-phase region
exists is termed the critical solution, temperature. In the case of the
phenol-water system, this is 66.80C (point H in Figure 1). All
combinations of phenol and water above this temperature are completely miscible
and yield one-phase liquid systems.
EXPERIMENTAL
METHODS:
Apparatus:
Test tubes and test tube
rack, thermometer, pipette, dropper, aluminium foil, measuring cylinder.
Chemical:
Distilled water, phenol, water
bath and ice
Experimental
Procedures:
1.
A tightly sealed tubes containing an
amounts of phenol and water is given to make a phenol concentration scale between
8% to 80%.
2.
Water bath is set up for 500C.
Test
tube
|
Phenol
|
Water
|
||
Volume(mL)
|
Percentage(%)
|
Volume(mL)
|
Percentage(%)
|
|
1
|
1.6
|
8
|
18.4
|
92
|
2
|
4
|
20
|
16
|
80
|
3
|
8
|
40
|
12
|
60
|
4
|
12
|
60
|
8
|
40
|
5
|
16
|
80
|
4
|
20
|
3.
The tubes are heated in a beaker
containing hot water bath.
4.
The water bath is stirred to get an even
heating and the test tubes are shaken slightly.
5.
The temperature for each test tubes are
measured and recorded at which the turbid liquid becomeclear.
6.
The temperature of the test tubes are
reduced gradually by removing them from the water bath.
7.
The temperature of the liquids are
recorded at which the liquid becomes turbid and two layers are separated.
8.
The average temperature are determined for
each of the test tubes at which two phases are no longer seen or at which two
phases exist.
RESULTS
AND CALCULATIONS:
Phenol composition (%)
|
8
|
20
|
40
|
60
|
80
|
Average Temperature
(˚C)
|
43.5
|
44
|
74
|
46.5
|
32.5
|
QUESTIONS:
Explain the effect of
adding foreign substances and show the important of this effect in pharmacy.
The addition of third
component will change the solubility between phenol and water. If the third component
is soluble only in one of the two different components in tubes, the solubility
of the mixture will decrease. For example, salt only dissolve in water to form
salt solution. So, it lowers the tendency of salt solution to miscible with
phenol. If the third component is soluble in both components, the solubility
will increase make the mixture form only one phase. The critical temperature of
the solution, where the specific temperature of the solution that have the
complete mutual solubility, will be disturbed. If the mutual solubility
decreased, the upper consolute temperature raised while the lower consolute
temperature lowered, but when the mutual solubility increased, the upper
consolute temperature lowered while the lower consolute temperature raised. In
pharmaceutical practice, the adding of the substances into the formulations of
liquid drug might end up by decreasing the mutual solubility which will then
decrease the efficacy and its availability to the patient’s body system.
DISCUSSION:
Phase rule is useful
device that relate the effect of the least number of independent variables upon
various phase that can exist in equilibrium at a given components.
Phase rule equation can
be expressed as:
F = C - P + 2
where,
F - the number of degrees
of freedom in the system
C - the number of
components
P - the number of phases
present
From
the experiment, all tubes form immiscible mixture between water and phenol where the composition of phenol in the solution are 8%, 20%, 40%, 60%,
80% each. The
solutions are cloudy at first. After the mixture is heated, the solutions
become miscible and colourless. Then, the process of cooling down makes the
mixture to form two layers and become immiscible. From the result, the graph is
plotted and n-shape of graph is obtained.
There
are several errors and precaution steps to get an accurate data in this
experiment. Firstly, we must avoid parallax error. Parallax error occurs when
the measurement of an object's length is more or less than the true length because
of your eye being positioned at an angle to the measurement markings. So, the
eyes must perpendicular to the meniscus of solution to gain accurate
measurement. The excess or less amount of solution cause change in percentage
of phenol and water.
Secondly,
the tubes must be sealed tightly. This is because, as we heat the tubes, the
evaporation and boiling process will occur and cause some of the sample to
release out to the surrounding. So, we need to use para film and ensure the
tubes are tightly sealed before putting it in the water bath.
Lastly,
we must take reading immediately after the reaction occur either after heated
or cool down. This is because the reaction occur in short time.
The curve in diagram
shows the limits of the temperature and the concentration within which two
liquid phases exist in equilibrium. Are under the graph will give two layer
between phenol and liquid. Other region will give homogenous of solution which
the mixtures are miscible – one layer. As the percentage of phenol increase,
the water-rich phase will decrease and the phenol-rich phase will increase.
According to phase rule, when the phenol and water are miscible
F = 2 – 1 + 2
F = 3
So, 3 variables need to
be fixed to define the system completely. From the experiment, the pressure is
fixed. Thus, the degree of freedom, F is reducing to 2 where the temperature
and concentration of the phenol need to be fixed.
When the mixture turn
immiscible,
F = 2 – 2 + 2
F = 2
As the pressure is fixed,
the degree of freedom, F reduces to 1. Only temperature needs to be fixed.
CONCLUSION:
The
critical temperature for phenol-water system is around 65 degree C. Phenol and water are
immiscible and a two phase system is formed between them. When the mixtures
were heated, phenol and water became completely miscible with each other and
single phase system was formed. Lastly, the errors made in this experiment should be avoided in
the future in order to obtain an accurate result.
REFERENCES:
1. Chemfarming,
2012. Importance of Solubility in Pharmacy. https://chempharming.wordpress.com/2012/12/04/importance-of-solubility-in-pharmacy/
[10th November 2015]
2. Online
Magazine for Analytical Laboratories, 2014. The Basic Principles of
Sieve Analysis. http://www.analytic-news.com/papers/detail/500.html [13th
November 2015]
3. Dexter
P, John B. 2007. Phase Diagrams (and Pseudosections) for Petrologists. http://serc.carleton.edu/research_education/equilibria/simplephasediagrams.html
[16th November 2015]
4. Campbell, F. C. 2012. Phase Diagrams—Understanding the Basics ASM International®
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