Practical 2: Phase Diagrams
Part B
Title: Mutual solubility
curve for phenol and water.
Objective: To understand
the phase diagram of phenol and water.
Theory:
Phenol and water are partially
miscible liquids, but here phenol is not really liquid, it is considered as
liquid since the addition of first part of water reduces the solid’s melting
point under room temperature to produce a liquid-liquid system. It forms a two
component systems containing liquid phases, below shows the
temperature-composition diagram.
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| Click to enlarge |
Referring the
figure above, the region outside the curve contains one liquid phase while the
region under the curve is where two liquid phases exist. This is when two
different layers can be seen. When the temperature is maintained at 50°C, it
will result in the formation of a single liquid phase until a point is reached,
at which a minute amount of second phase is observed.
Normally, the two liquids (phenol
and water) will become more miscible in each other with the increasing of the
temperature until where it reach a consulate temperature and beyond this
temperature, the liquid-liquid system will be completely miscible at any
measurement forming a one phase liquid. Most probably, any conjugated liquids
can form a close system, whereby there
is the existence of two consulate temperature at the top and bottom, but it is
not easily to determine the two temperature (before the substance become
evaporated or solidified) except with nicotine and water.
At any temperature below certain
critical solution temperature, the compositions for two liquid phases in
equilibrium are constant and are not affected by the relative amount of these
two phases. These phases are termed conjugate phases. The relative amounts of
the two phases vary. The miscibility between two partial miscible liquids is
normally affected by the existence of third component. All systems prepared on
a tie line, at equilibrium will separate into phases of constant composition.
Material: Phenol, water
Apparatus: Test tube,
parafilm, thermometer, water bath
Procedures:
1. 20 mL mixture of phenol and water are
prepared for every test tube.
2. For
mixture containing 8% concentration of phenol, the volume of phenol and water needed
to produce 20 mL mixture are calculated and measured using measuring cylinder.
3. The measured amount of water and phenol
are then transferred to a test tube.
4. Step 1-3
are repeated to produce mixtures containing phenol concentration scaled between
11%, 20%, 50%, 63%, 70% and 80%.
5. All of the
test tubes are then labeled before being placed in the water bath. The test
tubes are sealed with parafilm and a thermometer is poked through the parafilm
to measure the temperature.
6. The
water is stirred and if possible the tubes are shaked as well.
7. The
temperature at which the liquid becomes turbid and the two layers separate are
observed and recorded.
8. The
average temperature is determined.
9. The
graph of average temperature versus percentage of phenol is then plotted and the
critical solution temperature is determined.
Results:
Discussion:
In this experiment, two different components in liquid phase –
phenol and water are used. Phenol is partially miscible with water. Based on
the results obtained from the experiment, a curve is obtained in the graph
temperature versus percentage of phenol in water in volume. The curve shows the
limits of temperature and concentration within which two liquid phases exists
in equilibrium. The region outside this curve shows systems with only one
liquid phase whereas the region inside the curve contains systems with two
liquid phases.
As the concentration of phenol in water continues to increase, the
amount of phenol-rich phase will increase as well. However, once the
concentration of phenol in water exceeds a certain level, a single phenol-rich
liquid phase is formed.
From the curve, the critical solution or upper consulate temperature
is 67ºC. The critical solution or upper consulate temperature is the maximum
temperature at which the two-phase region exists. A line drawn across the
region containing two phases is termed a tie line and it is always parallel to
the base line in two-component systems. All systems prepared on the tie line,
at equilibrium, will separate into phases of constant temperature. These phases
are termed conjugated phases. Tie line in a phase diagram is used to
calculate the composition of each phase in addition to the weight of the
phases.
Among the precaution that is taken during the experiment is by
wrapping the top of conical flask with parafilm to avoid evaporation of phenol.
When taking readings from the thermometer, the eyes are ensured to be at the
right angle with the meniscus layer of the mercury level in the thermometer. As
phenol is a carcinogenic compound, gloves, goggles and mouthpiece are worn all
the time during the experiment.
There is a deviation of the upper consolute temperature because of
evaporation of some of the phenol. Besides, the amount of phenol used may not
be exactly accurate and the temperature may not be taken at the exact time when
two phases exist or two phases does not exist.
Conclusion:
The critical solution or consolute temperature for
phenol/water system is 67ºC.
References:
1. Martin’s Physical Pharmacy and Pharmaceutical Sciences, 5th
Edition, Patrick J. Sinko, Lippincott Williams and Wilkins, page 39, 40
2.
E.A.Moelwyn- Hughes. (1961). Physical Chemistry, 2nd Ed.
Pergamon. New York.
hello,
ReplyDeletecan i know how to draw the graph or the digram of this expirment?
what is its appication or use for pharmacy
ReplyDelete