Colligative Properties of an Cyclohexane/1-Propanol Mixture Vijay Kumar and Ben Williamson Washington State University, Chemistry 333

1
Colligative Properties of a Binary Liquid
Cyclohexane 2-Propanol A. Sinclair, C. Jordan
(Grunst), U. Dennis Washington State
University, Chemistry 335
Density Introduction With ideal conditions
partial molar volumes of a binary mixture are
independent of concentration. Therefore, we can
calculate a total volume by adding the two
individual partial volumes. The following
equation defines total volume In reality you
will not be able to add these volumes due to
intermolecular forces, so the following equation
allows us to determine liquid mixture
volumes. Procedure Pycnometer that are 25 mL
were cleaned, dried and then weighed. These same
pycnometers were then filled with the ten
different solutions, weighed and recorded. Then
by the use of the following equation various
densities were found. Results As shown
in our graph we had very similar result to the
reference data. The mixing caused only a slight
inconsistency from the ideal behavior. Conclusions
The reference values that we found for
cyclohexane and 2-propanol are 0.779 g/mL and
0.803g/mL respectively. Our values were
0.778360.001 for cyclohexane and 0.802220.002
for 2-propanol. These compare well to the
reference values. However, due to the
inconsistency of our solutions with the ideal
behavior we cannot assume that the partial molar
volumes are additive. Error Propagation
Surface Tension Introduction Surface tension
occurs because of the intermolecular forces in a
liquid. It produces a resistance between the
surface expanding or contracting. Under constant
temperature and pressure we can measure different
surface tensions due to the various
concentrations that we used. We calculated
surface tension using the simple relationship of
where ? is surface
tension in units of ergs/cm2. Procedure First,
in order to make sure the apparatus, Du Nouy
Tensiometer, was calibrated we placed a 100 mg
piece of paper on the meter and recorded a
measurement. We found that our correction factor
was 1.42. This was found by using the equation
mg/R mmass of paper, Rmeasurement reading, and
gacceleration of gravity. Then we placed our
various concentrations into the dish and recorded
the different measurements. We then made or
graph of mole fraction of cyclohexane versus
surface tension. Results Our results shown for
cyclohexane and 2-propanol are relatively similar
for the literature values that were found. For
cyclohexane our surface tension was equivalent
for the literature values of 25.5 dynes per cm2.
For 2-propanol the literature value was 23.78 and
our experimental value was 23.10.029 dynes per
cm2, a bit further off but still very
close. Conclusions The conclusions for this
experiment are that the surface tension does not
have a linear relationship with the
concentrations/compositions. Our percent errors
for the measured values were for 2-propanol,
0.421 and for cyclohexane 0.203. Error
Propagation References Bettelheim, Frederick
A. Experimental Physical Chemistry. W.B. Saunders
Company, Philadelphia 1971. Perry, R.H, and
D.W. Green. Perrys Chemical Engineers Handbook.
7th Edition. McGraw-Hill, New York
1997. Shoemaker, David P., Carl W. Garland, and
Joseph W. Nibler. Experiments in Physical
Chemistry. 6th Edition. McGraw-Hill, New York
1996. Surface Tension. Wikipedia
Encyclopedia. November 15th, 2006. WSU
Libraries. Washington State University,
Pullman, WA.lthttp//en.wikipedia.org/wiki/Surface_
tensiongt.
Viscosity Introduction Viscosity, (also called
the coefficient of viscosity), is the
proportionality constant between the force that
causes a laminar flow and velocity gradient of
that flow, over an area that is parallel to the
direction of the flow. The relationship
described can be illustrated with Newtons
law A Newtonian liquid near the walls of the
capillary tube can be considered stationary,
while the liquid in the center flows with the
greatest velocity in the center of the tube.
Procedure With the capillary viscometer, diameter
of 200 µm, we can calculate an unknown viscosity
using a known viscous liquid to calibrate the
apparatus and find the constant b for the
following equation t efflux
time ?density Then the constant, b, we can
solve for all the viscosities of our
ten solutions. Placing about 10 mL into the
viscometer we drew the liquid up using a vacuum
and then timed the liquid as it dropped from
mark a to mark b. This is our efflux time and
with this you then plot viscosity versus mole
fraction of cylcohexane. Results From
the data shown above we can see that the
viscosity is gradually decreasing with the
increase of the mole fraction of cyclohexane.
Our experimental cyclohexane has a viscosity of
1.02cP and 2-propanol has a viscosity of 2.04cP.
These compare nicely with the reference values
for cyclohexane and 2-propanol of 1.07cP and
1.97cP respectively. This gives us an error of
4.9 percent for cyclohexane and 3.4 percent for
2-propanol. Conclusions Using equation seven we
can see that the laminar layer separation versus
the molecular equilibrium separation will
decrease as viscosity decreases, or for our
example as the mole fraction of cyclohexane
increases. This shows that the solution is
becoming less viscous, meaning a larger laminar
layer and also that the molecular spacing will
increase more and thus the ratio laminar layer
separation versus molecular equilibrium
separation will decrease. Propagation of Error
Phase Diagram Introduction Liquid- Vapor phase
diagrams are an important tool used to represent
the distillation of a binary liquid pair. A
binary phase diagram is used to show the
relationship between the boiling temperature and
the composition of the liquid and the vapor in
equilibrium at a constant pressure. This phase
diagram shows no boiling point azeotrope.
Procedure Before performing the distillation
process, the refractive indices of the prepared
solutions were measured so that a standardization
curve could be created. The refractive indices
were plotted vs. the mole fractions. Mix
Cyclohexane and 2-propanol at various
concentrations and heat until equilibrium is
reached, Tboil. Record the temperatures and
collect samples of the distillate and residue.
Cool samples in a 20oC water bath. Refractive
indices were taken for all the samples. The
mixtures were made by placing small amounts of
cyclohexane into pure 2-propanol. These were for
our high concentration points for 2-propanol, the
liquid curve. Then the same method was repeated
and the vapor curve was produced by the high
concentrations for cyclohexane. Results From
the phase diagram below, there is no boiling
point azeotrope for the cyclohexane/ 2-propanol
mixture. As mentioned above, the
standardization curve was plotted by plotting the
index of refraction vs. mole fraction for each of
the prepared solutions. The data was fitted
using the most accurate method, or the method
with the best R2 fit, which in our case is a
polynomial fit. Conclusions By distilling a
cyclohexane/2-propanol mixture, it was found that
the system does not form a boiling point
azeotrope. Deviations in the phase diagram can
be accounted for since the data obtained was
taken at 700 mm Hg, compared to the ideal value
of 760 mm Hg. In addition, the binary mixture
was very volatile, and some of the vapor product
may have been lost to the surroundings when the
liquidus samples were taken. Furthermore, flash
vaporization may have occurred when cyclohexane
was added to the reaction flask.