Title
Determination
of Phase Diagram for Ethanol/ Toluene/ Water System Theory
Objectives
To
determine the phase diagram for three-component systems at constant temperature
and pressure.
Introduction
In
the phase diagram, each corner of the triangular diagram represents a pure
component,
which
is 100% A, 100% B, and 100% C. Phase diagrams for ternary systems are usually
represented
using a triangle . This graph accounts for the fact that only two variables are
required.
Along the phase boundary only one variable is required. If the line drawn is
hypothetical,
the real curve will be determined in this experiment. When the solution is
stirred,
the transition from one region to another can be observed by appearance (or
disappearance)
of cloudiness or turbidity in the solution. The turbidity results from
scattering
of
light by the large number of very small “oily” droplets of the second phase
that are
produced
when the system is stirred. Sometimes it is easier to see this when stopping
the
stirring
briefly. If the three components are mixed to give an overall system
composition that
falls
in the 2-phase region, the system will separate into two phases. The compositions of the
phases
that form are given by the intersections of a tie line with the phase boundary.
The tie
line
must also contain the point describing the overall system composition.
APPARATUS
Conical flask
Conical flask stopper
Retort stand and clamp
Pipette
Burette
CHEMICALS
Ethanol
Toluene
Distilled Water
Procedures
1.Mixtures
of ethanol and toluene is prepared in sealed containers measuring 100cm3 containing the following percentages of
ethanol (in percent): 10,25,35,50,65,75,90 and 95.
2.
20 ml of each mixture is prepared by filling a certain volume using a burette
(accurately).
3.
Each mixture is titrated with water until cloudiness is observed due to the
existence of 2nd phase.
4.
A little water is added and shaken well after each addition.
5.
The room temperature is measured.
6.
The percentage based on volume of each component is calculated when the second
phase starts to appear/ separate.
7.
The points are plotted onto a triangular paper to give a triple phase diagram
at the
recorded temperature.
8.
A few more measurements is done if necessary.
Results
%
Ethanol (v/v)
|
Volume
of water used (mL)
|
Average
|
|
Titration
I
|
Titration
II
|
||
10
|
1.5
|
2.0
|
1.75
|
25
|
1.9
|
2.3
|
2.10
|
35
|
2.4
|
3.2
|
2.90
|
50
|
3.1
|
4.0
|
3.55
|
65
|
5.5
|
5.0
|
5.25
|
75
|
6.5
|
8.3
|
7.40
|
90
|
11.4
|
13.0
|
12.20
|
95
|
18.6
|
21.2
|
19.90
|
1. Does the mixture containing 70% ethanol, 20%
water and 10% toluene (volume) appear
clear or does it form
2 layers?
The solution is appear
clear.
2. What will happen if you dilute 1 part of the
mixture with 4 parts of (a) water;
(b) toluene; (c) ethanol?
1 part x 70% ethanol = 1 part x 70/100 = 0.7
part of ethanol
1 part x 20% water = 1
part x 20/100 = 0.2 part of water
1 part x 10% toluene = 1 part x 10/100 = 0.1
part of toluene
~There are 0.7 part of
ethanol; 0.2 part of water; 0.1 part of toluene in the mixture.
a) 1 part of mixture + 4 parts of water:
Ethanol = 0.7/1+4 x
100% =14%
Water = 0.2 +4 / 1+4 x
100% = 84%
Toluene = 0.1 / 1+4 x
100% = 2%
From the phase diagram, this mixture is
outside the area of the binodal curve. Therefore, a
clear single liquid
phase of solution is formed.
b) 1 part of mixture + 4 parts of toluene
Ethanol = 0.7 / 1+4 x
100% = 14%
Water = 0.2 / 1+4 x
100% = 4%
Toluene = 0.1+4 / 1+4
x 100% = 82%
From the phase
diagram, this mixture is within the area of the bimodal curve. Therefore, a
two liquid phase will
form and the mixture is cloudy.
c) 1 part of mixture + 4 parts of ethanol
Ethanol = 0.7 / 1+4 x
100% = 14%
Water = 0.2 / 1+4 x
100% = 4%
Toluene = 0.1+4 / 1+4
x 100% = 82%
From the phase
diagram, this mixture is outside the area of the binodalcurve. Therefore, a clear
single liquid phase of solution is formed.
Discussion
A phase diagram is a
representation of the phases existing in equilibrium at any given
condition. According
to the Phase Rule, a maximum of four intensive properties must be
specified to totally
define the state of a three-component system. The usual intensive
variables are
pressure, temperature, and concentration. A phase diagram is a diagram
representing the
limits of stability of the various phases in a chemical system at equilibrium,
with respect to
variables such as composition and temperature.
There are few errors
in this experiment which caused the result obtained to not be
accurate. One of the
errors is, parallax error. The reading of the pipette is not obtained
accurately due to
wrong position of the eye. Secondly, the mixture was not shaken well after
addition of water and
this lead to poor results obtained. Ethanol and toluene are volatile
liquids. Their volume
may be less than the actual needed value as some of them have been
evaporated. This
affected the volume of water added for titration.
There are several precautions that should take
place during this experiment. Firstly, to
avoid parallax error,
the eyes should be perpendicular to the reading of the pipette.
Furthermore, the
mixture should be shaken well after addition of water so that it gives a
better result.
However, every group will have different results because the judgement of
cloudy solution
differs for each individual.
CONCLUSION
Ethanol,toluene and
water system is a ternary system with one pair of partially miscible
liquid (toluene and
water).
REFERENCES
1. Physicochemical Principles
of Pharmacy,
3rd edition
(1998) . A.T. Florence and
D.Attwood. Macmillan
Press Ltd.
2. Physical Pharmacy: Physical Chemistry
Principles in Pharmaceutical Sciences, by Martin,
A.N.
3. https://www.e-education.psu.edu/png520/m5_p5.html
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