CHAPTER
6
PARTIALLY MISCIBLE ANILINE-HEXANE SYSTEM
6.1 INTRODUCTION
Not
other;
all
liquids are completely miscible
with
in between this extreme and that of almost
immiscibility,
e.g.,
mercury
and
water,
each
complete
there
is
an
important type of system consisting of two liquids which are
partially
or
miscible. For example, if a little phenol,
ether
aniline is added to water at ordinary temperatures,
material
will dissolve completely, but if the
continued
a
point is reached when no
the
addition
further
is
dissolution
occurs and two liquid layers form. One of these layers is
saturated
the
solution of the organic substance in
water,
other is a saturated solution of water in
compound;
the
conjugate
two
and
the
organic
equilibrium
are
called
It is not necessary for
one
systems
solutions.
a
in
of
the
substances to be water, as incompletely miscible systems are
frequently
aniline
with
two
organic
compounds,
e.g.,
+ hexane and carbon-disulphide + methyl alcohol
ordinary
liquid
obtained
temperatures,
or
with an
organic
compound
sulphur or liquid phosphorous at high
at
and
temperatures.
It is of interest to consider the conditions of
equilibrium
in such systems of partially miscible liquids.
In
hexane
has
hexane
in
the
temperature,
slow
present investigation the system
been chosen for study. Aniline
in
aniline form two separate layers. At
the composition of these layers is
aniline
hexane
any
+
and
given
fixed.
On
warming, at a certain temperature, the composition
of
161
both
layers
becomes
the
same
when
there
is
complete
miscibility (homogenisation of the two layers).
A
aniline
new approach made now is that when two
layers
+ hexane (partially miscible in each other)
homogeneous
at
a characteristic temperature,
of
become
all
changes
occurring in interior of both the phases must be such as
tend
towards
tension,
phases
decrease
in
the
interfacial
such that just at the miscibility temperature
disappear. The internal pressure in each
therefore
be
miscibility
have
a progressive
to
a
assumed
to
temperature
significant
change
phase
may
upto
the
attained
must
analogously
at which the value
relationship with
the
that
in
the
pure
-
water
components at the same temperature.
Pugazhendhi
[57]
investigated the
system and found that at the critical
there
is
solution temperature
a unique turning point at which
corresponds
6.2
phenol
the
composition
to the reported value in literature.
EXPERIMENTAL PROCEDURE
Purified aniline (Robert Johnson Chemical, AR
India)
Grade,
and hexane (E.Merck, AR Grade, India) were used
for
the present study.
Different
ratios of aniline-hexane mixtures made
by
weight were taken in boiling test tubes. For each ratio,
at
the miscibility point the internal pressure
using
the
experimentally
measured
was
quantity
ultrasonic velocity, viscosity and density.
determined
namely,
162
6.3 RESULTS AND DISCUSSION
At
each
temperature
of
miscibility
computed
parameters are given in
of
two
the
constituents
is
the
reproduction
of
the
and
hexane,
at
meant
the
was calculated. Figure 6.1
classical
result
when
experimentally obtained miscibility temperature are
against
and
Table 6.1. For each ratio
aniline
temperature of miscibility Vm/Vf
measured
the
plotted
composition . In all these cases by composition
the
ratio
of weights of aniline
and
hexane
is
taken
experimentally . The so called critical solution temperature
or
the
consolute temperature for the system
is
given
Figure 6.2 wherein a plot of Vm/Vf versus composition
a
first
order
transition
at
the
critical
in
gives
solution
composition.
Consolute
with
the
whose
temperature is
also a
difference that the former is
miscibility
at
a
point
composition
miscibility temperature is the highest for the
system.
given
In other words above the consolute temperature
the
system remains in a completely homogeneous state.
Figure 6.3 gives
temperature,
where
a plot of Vm/Vf versus
the turning point happens
with consolute temperature. To make a sharp
composition
at
the
critical
miscibility
to
reading
solution
sharp
maximum
consolute
at
temperature
the molefraction
of
of the
temperature,
Ln{d(Vm/Vf)/dx^} versus molefraction of hexane was
A
coincide
plotted.
hexane
is seen to be obtained
from
at
the
Figure
6.4.
The
composition for the aniline - hexane system,
at
the consolute temperature, obtained herein (using Vm/Vf)
is
very reproducible and agrees with the literature value.
The
163
Table
6.1 Measured and computed properties
of
aniline (A) - hexane (B) system
Temp
Cone.
Of
u
P
„
»i
VB
vf
(g/cc)
(CP)
(atm)
(ml)
(ml)
vn/vf
Hexane
(•C)
(mf)
(cm/s)
45.1 0.150
146200 0.9401 1.1935 4308
97.947 0.1353 723.9
58.1 0.231
138400 0.9038 0.7809 3852 101.251 0.2333 434.1
64.0 0.319
140200 0.8630 0.6577 3318 105.330 0.3046 345.8
66.2 0.412
101000 0.7749 0.5398 3345 116.469 0.2478 469.9
66.0 0.513
127000 0.8256 0.5234 3090 108.477 0.3617 299.9
64.9 0.621
101900 0.7432 0.5318 3264 119.475 0.2507 476.0
60.4 0.737
101300 0.7164 0.3080 2424 122.831 0.5559 220.9
47.4 0.849
103400 0.6800 0.2874 2174 128.255 0.6280 204.2
MISCIBILITY TEMPERATURE ( *C)
164
0
0-1
0-2
0-3
0-4
0*5
04
0-7
04
0-9
MOLEFRACTIONS OF HEXANE (X| )
Figure 6.1
variation of miscibility temperature
with molefraction of hexane for the
aniline + hexane system
In
(V m /V f)
165
Figure 6.2
Variation of In (V_/Vf) with molefraction of hexane for the partially
miscible aniline -I- hexane system
W
v+
166
SO
60
MISCIBLE TEMPERATURE
Figure 6.3
Flot of Vm/Vf versus miscibility
temperature of aniline + hexane
system
In
t><V»n/Vf ) /< **]
167
MOLEFRACTION OF HEXANE (X|)
FIG 6i- 4- PLOT OF Ln {d(VrrVVf ) / dx] VERSUS MOLEFRACTION OF
HEXANE
{ ANILINE ♦ HEXANE
SYSTEM)
168
value of the consolute temperature of 66.2°C obtained herein
is
very
reproducible
literature
due
but
differs
from
value of 59.4*C. Plausibly this may
to
an
undetected impurity either
hexane,
as
it
impurity
that
on
is very well known that the
the
sensitivity
in
consolute
of
the
temperature
consolute
of
the
perhaps
be
aniline
or
in
effect
of
an
is
marked.
temperature
to
The
small
quantities of impurities is so classical that it is not only
reproducible
but used to know the concentration of a
known
added impurity.
These
(Vm/Vf)
at
results point to a significant
the
miscibility
temperature
importance
including
of
the
consolute temperature. Equation ( 5.5) namely ,
I
*1V
I3
vm/vf - I| -bRT
- I|
given
already
shows
that Vm/Vf is
a
function
of
molar
cohesive energy (w^V). Recalling the important quantitative
role of molar cohesive energy (JTjV) at the miscibility point
of
a
ternary
significant
miscible
system
discussed
in
Chapter
5,
that the cohesive energy density of a
it
is
ternary
phase represented by the linear Equation (5.8)
in
molefractions namely
3
Z
Xj (iriVJj
=
*rmVm
j=l
should
be
applicable also in the case of a
two
partially miscible system at the temperature of
as
component
miscibility
homogenisation of the two phases is common to
both
the
169
situations.
it
was
At a given temperature, in the ternary
the
third
component
that
was
systems
responsible
for
bringing about miscibility. However, in the case of a binary
partially
miscible
system it is the
temperature
that
is
responsible for homogenisation. Hence at each temperature of
miscibility including that at the consolute temperature
linear
relationship of molefractions namely Equation
the
(6.1)
should also be applicable.
Calculation
show
that,
at
each
temperature
miscibility, when homogenisation occurs, the above
is
relation
also valid but the deviations vary in the range
17%.
of
The explanation for such deviation may be as
of
10-
follows:
the properties of individual pure components were taken from
literature
of
the
molar
at convenient temperatures below and above
miscibility temperature. For
cohesive
properties
that
calculation
of
the
energies, interpolations were made
of
the
at the miscibility temperature. Thus
the individual property might in some way
errors
of
get compounded to
give deviations in the range of 10-17%. As mentioned earlier
in
connection
obtained
with the difference
in
the
experimentally
consolute temperature of 66.4*C instead of
59.4*C
reported in literature, this deviation of 10-17% may be
to some unknown impurity either in hexane
due
or aniline..
In conclusion it may be stated that if two immiscible
liquids
are to become homogenise either by the addition
third
component
linear
additions of the molefractions of
implied
in
by a variation of temperature
the
,
the
constituents
Equation (6.1) is that the miscibility
constituents is
the
or
of
of
two
conditioned by the minimum requirement that
molar free energy (ir^ Vm) is to be
the species in the
equipartitioned
ratio of their mole fractions.
by