PRACTICAL 1
Title : Phase diagram for ethanol/toluene/water system
Objective : To
determine the phase diagram for ethanol/toluene/water system theory
Introduction :
In three-component
system at constant temperature and pressure, the composition can be expressed
in coordinates form of triangular diagram
A
Figure 1 : Ternary Phase Diagram.
In the above
diagram, each corner of the triangle represent one pure component, that is 100
%A, 100%B and 100%C. Each side of the triangle represent two-component mixture
and in this triangle represent ternary component. Any line that is parallel
with one side of the triangular diagram show the constant percentage value for
a component, such as DE show 20%A with any amount of B and C. Line FG also show
all mixture consists of 50%B. These lines intersect at K which contains 20%A,
50%B and 30%C. Measurement can be made like this, it is because sum of all the
distance from K which draw parallel to the three sides of the triangle are the
same and equal length with anyone from the side the triangle in the triangular
diagram.
Addition of the
third component to one pair liquid-liquid which is miscible can change the
solubility of them. If the third component is more soluble in one of these two
component, solubility of both liquid will decrease, but if it is soluble in
both component, their solubility will increase. Hence when ethanol is added to
one mixture of benzene and water, solubility of these two component will
increase until achieve a point where this mixture become homogeneous. This method is used in
formulation of liquids. Examples of 3 liquids component system which had been
tested include castol oil/alcohol/water ;”minyak permen”/glycol
propylene/water, “minyak permen”/glycol polyethylene/water.
Advantage in
preparing an oily ingredient as a homogeneous liquid aqueous is very obvious.
However, we need to know what will happen to a system like this when it is
diluted and this can be explained through the understanding of the triangular
phase diagram. Figure 1 is for system and components of “minyak
permen”polysorbate20-water. One concentration of 7.5%oil, 42.5% of polysorbate
20 and 50% of water ( point A in diagram) can be diluted for 10 times with water, giving one clear
solution ( still having 0.75% oil, 4.25% polysorbate 20 and 95% of water ) However, when 1mL of water is added to 10mL:
of clear solution B ( 49% oil, 50% polysorbate 20,1%water) solution becomes
cloudy, point B’(44.5% oil, 45.45% polysorbate 20 and 10 %water). If add 1mL of
water continuously, solution will become clear, point B’’ ( 40.5% oil,41.3% polysorbate 20,
18.2%water) but the original solution if have been dilutied 3 times ( 16.33%
oil, 16.33% polsorbate 20, 67.33 % water) solution becomes cloudy.
Chemicals :
Ethanol, toluene and
distilled water
Apparatus
Conical flask, conical
flask stopper, retort stand and clamp, pipette, and burette.
Procedures:
1. Mixtures of ethanol and toluene which containing percentages
of ethanol : 10, 25, 35, 50, 65, 75, 90 and 95 were prepared in a 100 cm3 closed conical flask.
2. 20mL of each mixture was prepared by adding the needed
volume of solution using a burette to obtain an accurate volume.
3. The pipette was filled with water.
4. Each of the mixture was titrated with the water until a
cloudy solution formed result from the formation of two phase system.
5. Water was added drop by drop and the conical flask was
shaken vigorously after each addition.
6. The volume of water used for each titration recorded.
7. The percentage according to the volume of each component
when the two phase system observed
was calculated.
8 The point was plotted in the triangular coordinate graph
paper.
9. The experiment was repeated again to obtain more accurate
result.
Results :
Percentage of
ethanol (%)
|
Volume of ethanol(mL)
|
Volume of toluene
(mL)
|
Volume of water
used(mL) in 1st test
|
Volume of water
used(mL) in 2nd test
|
Average volume of
water used (mL)
|
10
25
35
50
65
75
90
95
|
2.0
5.0
7.0
10.0
13.0
15.0
18.0
19.0
|
18.0
15.0
13.0
10.0
7.0
5.0
2.0
1.0
|
0.5
0.8
1.0
1.8
3.0
4.6
10.8
15.8
|
0.6
0.7
1.1
2.2
3.4
4.8
11.0
16.2
|
0.45
0.75
1.05
2.20
3.20
4.70
10.9
16.0
|
Total volume of mixture(mL)
|
Ethanol
Volume
Percentage
(mL) (%)
|
Toluene
Volume Percentage
(mL) (%)
|
Water
Volume Percentage
(mL) (%)
|
|||
20.45
20.75
21.05
22.20
23.20
24.70
30.90
36.00
|
2.0 9.8
5.0 24.1
7.0 33.3
10.0 45.0
13.0 56.0
15.0 60.7
18.0 58.3
19.0 52.8
|
18.0 88.0
15.0 72.3
13.0 61.8
10.0 45.0
7.0 30.2
5.0 20.2
2.0 6.5
1.0 2.8
|
0.45 2.2
0.75 3.6
1.05 4.9
2.20 10.0
3.20 13.8
4.70 19.1
10.9 35.2
16.0 44.4
|
Diagram : Phase
diagram of water-toluene-ethanol
Question :
1. Does the mixture containing 70%ethanol, 20% water
and 10% toluene(volume) appear clear or
does it form two layers?
The solution appear clear.
2. What will happen if 1 part of the mixture is diluted with
4 parts of (a) water (b) toluene (c) ethanol ?
Let assume that 1 part of solution = 100mL
So, 4 parts = 400mL
(a) Original volume :
70% ethanol = 70mL
20% water = 20mL
10% toluene = 10mL (Total
volume = 100mL)
After dilution with 400mL water
70%ethanol= 14%
20% water = 84%
10% toluene = 2 %
(Total volume = 500mL )
From the graph, the point A is inside two liquid phase,
hence cloudy solution is formed
(b) Original volume :
70% ethanol = 70mL
20%water = 20mL
10%toluene
=10mL (Total volume = 100mL )
After dilution with 400mL toluene
70%ethanol = 14%
20%water = 4%
10%toluene = 82%
(Total volume = 500mL )
From the graph, pint B is inside the two liquid phase, hence
cloudy solution is formed
(c) Original volume :
70%ethanol = 70mL
20%water =
20mL
10%toluene=
10mL (Total volume = 100mL )
After dilution with 400mL of 70%ethanol
70%ethanol = 94%
20%water= 4%
10%toluene= 2%
(Total volume = 500mL )
From the graph, point C is outside the two liquid phase,
locating single, hence clear solution is seen
Discussion :
Phase diagram for ternary systems
is usually represented using a triangle. Each of the three corners or apexes of
the triangle represent 100% by weight of one component ( ethanol, water or
toluene). As a result, that same apex will represent 0% of the other two
components. The three lines which join the corner points represent
two-component mixtures of the three possible combinations of ethanol, water and
toluene. Therefore the lines ethanol-toluene, toluene-water, and water-ethanol
are used for two component mixtures of ethanol and toluene, toluene and water,
water and ethanol, respectively. The area within the triangle represents all
the possible combinations of ethanol, toluene and water to give three-component
systems.
In this practical,water and toluene
are partially miscible, so when mixing usually forms two-phase system. The
heavier of the two phases consists of water saturated with toluene, while the
lighter phase is toluene saturated with water. However, ethanol is completely
miscible with both toluene and water. It shows that addition of sufficient
alcohol to two-phase system of water and toluene will produce a single liquid
phase which make the three components miscible.
The result of this experiment has been plotted on a triangular
diagram as shown in diagram 1. The curve plotted on the triangular diagram is
known as the bimodal curve. The region below the curve represent a two phase
system. The mixture found in this region are cloudy and there is an obvious
separation of two phases. Although ethanol is miscible with both water and
toluene, the immiscibility of water and toluene is more than the homogenous
effect brought about by ethanol alone. Therefore,the amount of ethanol is
insufficient to produce a homogenous one phase mixture. However the systems
found in region above the curve are one phase systems. The amount of
ethanol in these systems enough to
produce a homogenous mixture and a clear mixture is obtained for the systems
found in this region.
Some experimental errors maybe
happen in the experiment and cause inaccurate result formed. Firstly, when taking
reading on burette , the eyes of observer maybe not parallel to the meniscus
level of the water which caused reading of volume taken and recorded wrong.
Secondly, the conical flask is not swirled well after each addition of water
and this may result inaccurate volume of water was taken. Furthermore, judgment
of cloudy solution formed depends on personal judgment as the cloudiness is not
obviously seen.
Conclusion :
Ethanol, toluene and water system is a ternary system with
one pair of partially miscible liquid( toluene and water).
Reference :
1)
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/DOWNSTREAM/ternary.htm
2) Physical pharmacy : Physical chemistry Principles in
Pharmaceutical sciences, by Martin
A.N.
3) Physicochemical Principles of Pharmacy , 3rd edition
(1998) . A.T. Florence and D.Attwood. Macmillan Press Ltd.
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