Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
P. Narayana Murthy
The viscosities, densities and ultrasonic velocities of binary liquid mixtures of Anisaldehyde with o-xylene, m-xylene and p-xylene have been measured at temperatures (303.15, 308.15, 313.15 and 318.15) K over the entire range of mole fraction. These data have been used to evaluate adiabatic compressibility (β), free volume (Vf), free length (Lf) internal pressure (π) and enthalpy (H). Excess values of above parameters have also been calculated and fitted to the Redlich-Kister polynomial relation to estimate the binary coefficients and standard errors. The excess values of adiabatic compressibility and free volume are negative for all the binary mixtures. The results are interpreted in terms of molecular interactions present in the mixtures.
Received: August 04, 2011;
Accepted: November 24, 2011;
Published: January 18, 2012
The ultrasonic velocity measurements play an important role in understanding
the physicochemical behavior of liquids. Being sensitive to very low population
densities at high energy states, ultrasonic methods are reported to be complimentary
to the other techniques like dielectric relaxation, infrared spectroscopy, nuclear
magnetic resonance, etc. Thermodynamic properties derived from the measurement
of ultrasonic velocity, density and viscosity for binary mixtures are useful
in understanding the nature and type of intermolecular interactions between
the component molecules (Saravanakumar et al., 2010;
Singh et al., 2005). Excess thermodynamic properties
of mixtures are useful in the study of molecular interactions and arrangements.
Nain et al. (2010) and Singh
et al. (2004) have carried out investigations of thermophysical properties
of binary liquid mixtures containing aromatic ethers.
In order to study, the thermodynamic properties and molecular interactions
in the mixture of anisaldehyde with o-xylene, m-xylene and p-xylene, the ultrasonic
velocity (U), density (ρ) and viscosity (η) over the entire range
of composition at (303.15, 308.15, 313.15 and 318.15) K are reported in the
present study. The experimental values of u, ρ and η were used to
calculate the adiabatic compressibility (β), free volume (Vf),
free length (Lf), internal pressure (π) and enthalpy (H). From
these results the excess parameters have been calculated and fitted to the Redlich-Kister
type (Redlich and Kister, 1948) polynomial equation
to derive the binary coefficients and the standard deviations between experimental
and calculated results.
MATERIALS AND METHODS
The chemicals used were of analar grade and obtained from SRL Chemicals, Mumbai.
They were purified by standard procedure (Perrin and Armarego,
1988). The purity of samples was checked by comparing the densities, ultrasonic
velocities and viscosities of the pure compounds at 303.15 K with the available
literature as shown in Table 1. Jobs method of continuous
variation was used to prepare the mixtures of required proportions. The prepared
mixtures were preserved in well-stoppered conical flasks. After mixing the liquids
thoroughly, the flasks were left undisturbed in order to allow them to attain
The densities of pure liquids and liquid mixtures were measured by using a
specific gravity bottle with an accuracy of ±0.5%. An electronic balance
(Shimadzu AUY220, Japan), with precision of ±0.1 mg was used for the
mass measurements. An average of 4-5 measurements was taken for each sample.
Viscosities were measured at the desired temperature using Ostwalds viscometer,
which was calibrated using water and benzene. The flow time has been measured
after the attainment of bath temperature by each mixture. The flow measurements
were made with an electronic stopwatch with a precision of 0.01 sec. The viscosities
were obtained from the following relation:
where, k, ρ and t are viscometric constant, density of liquid and time
of efflux for a constant volume of liquid, respectively. The values are accurate
to ±0.001 mPa.s.
The ultrasonic velocities were measured by using a single crystal ultrasonic
pulse echo interferometer (Model: F-80X Mittal enterprises, India) which consists
of a high frequency generator and a measuring cell. The measurements of ultrasonic
velocities were made at a fixed frequency of 3 MHZ. The capacity of the measuring
cell is 12 mL. The equipment was calibrated by measuring the velocity in carbon
tetrachloride and benzene. The results are in good agreement with those reported
in literature (Lide and Frederikse, 1995). The ultrasonic
velocity has an accuracy of ±0.5 m sec-1. The temperature
was controlled by circulating water around the liquid cell from thermostatically
controlled constant temperature water bath with an accuracy of ±0.01
From the experimental data of density, viscosity and ultrasonic velocity, various thermodynamic parameters are evaluated using standard equations mentioned below:
where, b is a packing factor, K is a dimension less constant (Pandey
et al., 1993a) independent of temperature and nature of liquids and
its value is 4.28x109 and η is the viscosity. The other symbols
have their usual meaning.
where, Meff is the effective molecular weight and K is proportionality constant which is sensitive to molecular phenomenon.
||Intermolecular free length:
where, KT is the temperature dependent constant.
where, Vm is the molar volume and π is the internal pressure.
||Excess Gibbs free energy of activation:
The strength of interaction between the component molecules of binary mixtures
is well reflected in the deviation of the excess functions from ideality (Pandey
et al., 1993b). The excess properties such as βE,
VfE, πE, HE and LfE
have been calculated using the equation:
YE = Ymix
where, YE is βE or VfE or πE or LfE or HE and x represent mole fraction of the component and subscript 1 and 2 for the components 1 and 2.
The excess values of above parameters for each mixture have been fitted to Redlich-Kister polynomial equation:
The values of the coefficients ai were calculated by method of least squares along with the standard deviation σ (YE). The coefficient is adjustable parameters for a better fit of the excess functions. The standard deviation values were obtained from:
where, m is the number of experimental points, n is the number of parameters, Yexpt and Ycal are the experimental and calculated parameters, respectively.
RESULTS AND DISCUSSION
The experimental results of ultrasonic velocity, density and viscosity of the
pure liquids at 303.15 K are compared with the published data in Table
1. The values of ultrasonic velocity, density and viscosity were taken for
all the three mixtures at four different temperatures and are shown in Table
|| Ultrasonic velocity (U), density (ρ) and viscosity (η)
for the binary systems at varying temperatures
From these values, various acoustical parameters like adiabatic compressibility,
free length, free volume, internal pressure and enthalpy have been evaluated.
The excess values of some of the acoustic parameters are also calculated and
are presented in Table 3. The values of the Redlich-Kister
polynomial coefficient, ai evaluated by the method of least squares
along with the standard deviation is given in Table 4. Plots
of πE, UE, G*E and HE against
mole fraction of anisaldehyde for all the three systems are given in Fig.
From Table 2, it can be observed that the ultrasonic velocity (U) of binary mixtures at each mole fraction decreases with increase of temperature. Also it is observed that at each temperature, as anisaldehyde mole fraction increases, the ultrasonic velocity, density and viscosity of the mixtures increase. The order of interactions among the mixtures is observed as anisaldehyde+o-xylene>anisaldehyde+m-xylene> anisaldehyde+p-xylene.
Adiabatic compressibility, β is found to be decreased with increase in
the concentration of anisaldehyde. It is primarily the compressibility that
changes with structure, which leads to a change in ultrasonic velocity. The
change in adiabatic compressibility in liquid mixtures indicates that there
is a definite contraction on mixing and the variation may be due to complex
||Excess Internal pressure (πE) as a function
of mole fraction of anisaldehyde (x1) for anisaldehyde+o-xylene
(a), anisaldehyde+m-xylene (b) and anisaldehyde+p-xylene (c) at different
||Excess ultrasonic velocity (UE) as a function of
mole fraction of anisaldehyde (x1) for anisaldehyde o-xylene
(a), anisaldehyde+m-xylene (b) and anisaldehyde+p-xylene (c) at different
|| Excess Free length (LfE), Excess adiabatic
compressibility (βE) and excess free volume (VfE)
for the binary systems at varying temperatures
|| Redlich-Kister Coefficients (ai) and standard
deviation (σ) for the binary systems at varying temperatures
It clearly shows that there are some significant interactions between the molecules
of the mixtures taken under study. Intermolecular free length (Lf)
shows a similar behavior as reflected by adiabatic compressibility. The decrease
in compressibility brings the molecules closer, resulting in a decrease of intermolecular
free length. Intermolecular free length is a predominant factor in determining
the variation of ultrasonic velocity in the mixtures. The decrease in the values
of adiabatic compressibility and the free length with increase in ultrasonic
velocity further strengthens the strong molecular interactions between the unlike
molecules through hydrogen bonding.
It is also observed that there is decrease in free volume and increase in internal pressure with increase in mole fraction of anisaldehyde for all the three systems. It shows the presence of strong interactions and hence, supports the present investigation. In order to understand in a better way, the nature of molecular interactions between the components of the liquid mixtures, the discussion can be extended to excess parameters.
The results of excess values of compressibility, βE of anisaldehyde+o-xylene,
anisaldehyde+m-xylene and anisaldehyde+p-xylene are shown in Table
3 and are observed to be negative. The negative values of βE
suggest that the mixtures are less compressible than the corresponding ideal
mixtures which signifies chemical effect including charge transfer forces, formation
of H bonds and other complex forming interactions making negative contributions
towards βE and positive contributions towards G*E
(Parveen et al., 2009a). Also it is observed
that in case of all the mixtures at each temperature, as mole fraction of anisaldehyde
increases, the βE values of the binary mixtures attain a minimum
value at the mole fraction 0.5. Beyond this, the βE values of
the mixture increases with the increase of mole fraction of anisaldehyde. However,
the change in βE with temperature has been observed to be small
for the mixtures anisaldehyde+p-xylene. Similar behaviour was reported by Gupta
et al. (2006) and Iloukhani et al. (2005),
who worked on binary mixtures.
The excess properties of the mixtures are influenced by three main contributions, viz. (1) physical : due to non-specific Vander Waals type forces, (2) chemical : due to hydrogen bonding, dipole-dipole and donar-acceptor interactions between unlike molecules and (3) structural: due to the fitting of smaller molecules into the voids created by the bigger molecules. The first effect leads to contraction in volume and hence, leads to positive contribution towards HE and negative contribution towards UE and πE. In case of all the three mixtures, the ΠE values are found to be negative for the mole fraction range of 0.0 to 0.7. The negative contribution of πE value (Fig. 1) is an evidence of presence of stronger molecular interactions between the components present in the mixture. Further, the values of πE are more negative in anisaldehyde+m-xylene and anisaldehyde+p-xylene when compared to anisaldehyde+o-xylene mixtures.
VfE is found to be negative for all the mixtures over
the entire composition range of anisaldehyde. As temperature rises, VfE
values decreases in the mixtures. The negative values of VfE
suggest the existence of strong dipole-dipole interactions due to hydrogen bonding
among the molecules (Parveen et al., 2009b).
The plots (Fig. 2) of deviation in ultrasonic velocity, UE
with mole fraction at all the four temperatures for all the three mixtures exhibit
positive values. The positive values of UE decrease with increase
in temperature which indicates the decrease of strength of interactions with
temperature in all the systems. The higher positive values of UE
are observed in case of the anisaldehyde+p-xylene when compared with other two
mixtures. It confirms that anisaldehyde+p-xylene exhibits higher molecular interactions
when compared to other two mixtures. Similar results of UE have been
observed by Chorazewski (2007).
||Excess Gibbs free energy of activation (G*E)
as a function of mole fraction of anisaldehyde (x1) for anisaldehyde+o-xylene
(a), anisaldehyde+m-xylene (b) and anisaldehyde +p-xylene (c) at different
||Excess Enthalpy (HE) as a function of mole fraction
of anisaldehyde (x1) for anisaldehyde+o-xylene (a), anisaldehyde+m-xylene
(b) and anisaldehyde+p-xylene (c) at different temperatures
Figure 3 indicates the variation of G*E with mole
fraction of anisaldehyde at different temperatures for all the mixtures, respectively.
In case of all the three mixtures, G*E values are almost positive.
It indicates the presence of strong intermolecular interactions through hydrogen
bonding between the molecules of the mixtures. Subha et
al. (2004) made the similar results. The positive values of G*E
in each system attain a maximum value at all temperatures at the mole fraction
of 0.8. It suggests that an increase in intermolecular interaction between unlike
molecules is due to thermal energy. However, G*E value with temperature
is small in anisaldehyde+o-xylene mixture when compared to other two mixtures.
The values of HE can be interpreted in terms of the formation of
intermolecular hydrogen bonding and the breaking of associated structures of
anisaldehyde with o-xylene, m-xylene or p-xylene. In case of all the three mixtures,
the HE values (Fig. 4) are found to be negative
for the mole fraction range of 0.0-0.7. The negative values of HE
in the mixtures indicate the presence of stronger interactions between unlike
molecules. However, as mole fraction of anisaldehyde increases from 0.7-1.0,
the HE values are found to be positive. The positive values of HE
indicate that the interactions among the molecules lead to weak dispersion type
of forces arrived due to rupture of hydrogen bonding in the structure. Similar
variations in HE with change in composition has also been reported
by Misra et al. (2007).
In the present investigation, the excess adiabatic compressibility βE,
excess free volume VfE exhibit negative values over the
entire range of composition in case of all the three mixtures. It clearly indicates
the presence of strong hydrogen bonding interactions between unlike molecules
(Fort and Moore, 1965). This also may be quantitatively
interpreted in terms of closer approach of unlike molecules leading to reductions
in compressibility and volume (Jayakumar et al.,
1996). Further, πE which is usually discussed in terms of
molecular interactions, whose negative excess values for all the systems suggests
that strong molecular association between the unlike molecules. The positive
values of G*E and UE in case of all the three mixtures
supports the interpretation given above in terms of strong interactions. On
comparing the above results for the three mixtures, the strengths of interactions
xylene (b) and anisaldehyde+p-xylene (c) at different temperatures are observed
in the following order anisaldehyde+m-xylene>anisaldehyde+p-xylene> anisaldehyde+o-xylene.
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