Experiment 1
Part
B: Phase Diagrams –
Mutual Solubility curve for phenol and water
Objectives:
- To measure the miscibility temperatures of several water-phenol mixtures of known composition.
- To determine the phase coexistence line (miscibility temperature versus composition) and the critical composition and temperature calculated.
- To measure the effect of a third component on the water-phenol critical point.
Introduction:
Liquids such as
ethanol and water are miscible with each other in all proportions. Other
examples such as etherwater, phenol-water (Note that the phenol here is not
really liquid, but is considered to be so since the solid’s melting point under
room temperature is reduced by the addition of the first part of water in order
to produce a liquid-liquid system) have miscibility in limited proportions in
other liquids.
As temperature keeps
rising, usually both liquids become more soluble until the critical solution
temperature or consolute point is attained. The liquids will become completely
miscible after reaching above this point. Any pair of liquids can form a closed
system, whereby both upper and lower critical solution temperature exist. Both
temperatures (before the substance freezes or evaporates) are not easily to
determine except for nicotine and water.
The composition for
two layers of liquids in equilibrium state is constant and does not depend on
the relative amount of these two phases at any temperature below the critical
solution. Also, the presence of a third component will influence the mutual
solubility for a pair of partially miscible liquids.
Materials &
Apparatus:
8 boiling tubes,
beaker, measuring cylinder, pipette, water bath, parafilm sealed thermometer,
water and phenol solution.
Procedure:
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Test tube
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Percentage of phenol
(%)
|
8
|
11
|
23
|
38
|
50
|
63
|
71
|
80
|
Volume of phenol
(mL)
|
1.6
|
2.2
|
4.6
|
7.6
|
10.0
|
12.6
|
14.2
|
16.0
|
Volume of water (mL)
|
18.4
|
17.8
|
15.4
|
12.4
|
10.0
|
7.4
|
5.8
|
4.0
|
- Each of the test tubes was heated in a water bath. Remember to always stir the water and shake the tubes as well.
- The temperature for each of the tube at which the turbid liquid becomes clear was observed and recorded.
Test tube
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
Percentage of phenol
(%)
|
8
|
11
|
23
|
38
|
50
|
63
|
71
|
80
|
Volume of phenol
(mL) |
1.6
|
2.2
|
4.6
|
7.6
|
10.0
|
12.6
|
14.2
|
16.0
|
Volume of water
(mL) |
18.4
|
17.8
|
15.4
|
12.4
|
10.0
|
7.4
|
5.8
|
4.0
|
Temperature at which
turbid liquid becomes clear ( ̊ C)
|
40
|
52
|
59
|
67
|
63
|
53
|
49
|
34
|
Temperature at which
liquid becomes turbid ( ̊ C)
|
37
|
50
|
61
|
69
|
60
|
50
|
47
|
35
|
FIGURE 1: GRAPH PERCENTAGE OF PHENOL AGAINST TEMPERATURE AT WHICH
THE TURBID LIQUID BECOME CLEAR
Discussion:
Miscibility is the property of
substances to mix in all proportions, forming a homogeneous solution. The term
is most often applied to liquids, but applies also to solids and gases. Water
and ethanol, for example, are miscible because they mix in all proportions.
As for phenol and water, phenol is
partially miscible with water. Thus, in the graph it shown that, below the
curve there are two phase of liquid while the upper region of the curve is for
one liquid phase which after the phenol and water is miscible with each other.
Based on the result, temperature which
the turbid become clear is the temperature at which the double phase of phenol
and water become a single phase of liquid. While for the temperature at which
the clear water become turbid is the temperature at which the single phase
liquid become a double phase.
The highest temperature stated for the
double phase turned to a single phase is 66.8 degree Celsius.
The errors that can be detected in this
experiment are the tube is not tightly sealed, thus phenol will evaporate so
this will reduce the concentration of phenol in tubes. We also maybe not aware
when the solution might become separated in two layers and causes the
temperature recorded to be not accurate. Besides, we use measuring cylinder to measure
the amount of phenol and water, so it might causes the concentration to be
inaccurate.
The precaution that can be taken in this
experiment are after the addition of phenol into the conical flask, the top of
conical flask should be wrap with the film with thermometer in the middle to
avoid evaporation of phenol. Besides, we use phenol in this experiment, as we
know phenol is an acidic and carcinogenic compound, thus extra care should be
taken such as wearing a gloves and protective goggle.
Conclusion:
The critical solution temperature for
the experiment is 66.8 degree Celcius. The phenol and water are partially immiscible. The
double phase of phenol and water turned into single phase at 66.8 degree
Celcius.
References:
- Martin, A.N. 2006. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences. 5th Ed. Philadelphia: Lea & Febiger.
- Florence, A.T. & Atwood, D. 2006. Physicochemical Principles of Pharmacy. 4th Ed. New York: Macmillan.
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