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Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures



K. Narendra, Ch. Srinivasu and P. Narayana Murthy
 
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ABSTRACT

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.

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  How to cite this article:

K. Narendra, Ch. Srinivasu and P. Narayana Murthy, 2012. Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures. Journal of Applied Sciences, 12: 136-144.

DOI: 10.3923/jas.2012.136.144

URL: https://scialert.net/abstract/?doi=jas.2012.136.144
 
Received: August 04, 2011; Accepted: November 24, 2011; Published: January 18, 2012



INTRODUCTION

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. Job’s 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 thermal equilibrium.

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 Ostwald’s 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:

η = k . ρ . t
(1)

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 K.

From the experimental data of density, viscosity and ultrasonic velocity, various thermodynamic parameters are evaluated using standard equations mentioned below:

Adiabatic compressibility:

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(2)

Internal pressure:

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(3)

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.

Free volume:

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(4)

where, Meff is the effective molecular weight and K is proportionality constant which is sensitive to molecular phenomenon.

Intermolecular free length:

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(5)

where, KT is the temperature dependent constant.

Enthalpy:


Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(6)

where, Vm is the molar volume and π is the internal pressure.

Excess Gibb’s free energy of activation:

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(7)

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 – [x1Y1+x2Y2]
(8)

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:

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(9)

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:

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
(10)

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 2.

Table 1: Experimental and literature values of ultrasonic velocity (U), density (ρ) and viscosity (η) of pure liquid components at 303.15 K
Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
*Expt: Experimental value, *Lit: Literature value, Bhaskaran and Kubendran (2008), Al-Kandary et al. (2006)

Table 2: Ultrasonic velocity (U), density (ρ) and viscosity (η) for the binary systems at varying temperatures
Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different 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. 1-4, respectively.

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 formation.

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
Fig. 1(a-c): 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 temperatures

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
Fig. 2(a-c): 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 temperatures

Table 3: Excess Free length (LfE), Excess adiabatic compressibility (βE) and excess free volume (VfE) for the binary systems at varying temperatures
Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures

Table 4: Redlich-Kister Coefficients (ai) and standard deviation (σ) for the binary systems at varying temperatures
Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different 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).

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
Fig. 3(a-c): Excess Gibb’s 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 temperatures

Image for - Excess Properties of Binary Mixtures of o-xylene, m-xylene and p-xylene with Anisaldehyde at Different Temperatures
Fig. 4(a-c): 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).

CONCLUSION

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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