Ultrasonic investigation of induced dipole-induced dipole interactions in binary liquid mixtures at 298K

Size: px

Start display at page:

Download "Ultrasonic investigation of induced dipole-induced dipole interactions in binary liquid mixtures at 298K"

Piers Hicks
5 years ago
Views:

1 Indian Journal of Pure & Applied Physics Vol. 44, November 2006, pp Ultrasonic investigation of induced dipole-induced dipole interactions in binary liquid mixtures at 298K V Kannappan # & R Jaya Santhi # Postgraduate and Research Department of Chemistry, Presidency College, Chennai Department of Chemistry, Auxilium College, Vellore Received 4 July 2005; revised 18 October 2005; accepted 4 September 2006 Induced dipole-induced dipole interactions have been studied in binary liquid mixtures of benzene, n-hexane, carbon tetra chloride and p-xylene with cyclohexane by ultrasonic velocity (U), density (ρ) and viscosity (η) measurements at 298K and at different mole fractions. Acoustical parameters such as adiabatic compressibility (β), free volume (V f ) internal pressure (π i ), intermolecular free length (L f ), available volume (v a ), cohesive energy (CE) Rao constant (R) and molecular interaction parameter (χ U ) were calculated from the experimental data. The ultrasonic investigations on four binary liquid systems reveal that in the liquid mixture containing non-polar liquids, there exist weak induced dipole-induced dipole attractions. The strength of this type of intermolecular attraction depends on the polarizability of molecules of the components present in the mixture. Keywords: Interactions, Induce dipole, Mole fractions, Polarizability, Adiabatic Compressibility, Ultrasonics, Binary liquid mixtures IPC Code: B01J 19/10 1 Introduction Considerable scientific and practical interest has been stimulated by the investigation of organic liquids by ultrasonic measurements 1-3. Studies involving density and viscosity measurements are important for elucidation of ion-solvent, ion-ion and solvent-solvent interactions in mixed solvent systems. The nature and degree of molecular interactions in different solutions depend upon the nature of the medium, the structure of the solute molecule and also the extent of solvation 4,5 taking place in solution. Basically, a binary mixture is formed by the replacement of like contacts in pure liquids by unlike contacts in the mixture. Ultrasound velocity measurements have been extensively applied to assess the molecular interactions in pure binary 6-8 and ternary 9-11 liquid mixtures. In binary mixtures containing non-polar components, there can be only induced dipoleinduced dipole interactions, which arise due to polarizability aspects. The forces of attraction due to induced dipole-induced dipole are very weak and optical methods cannot be used to detect and access these interactions. Literature survey showed that very few studies have been done on the induced dipoleinduced dipole interactions in binary liquid mixtures. Hence, an attempt has made to measure the ultrasonic velocity, density and viscosity in order to assess the weak dispersion interactions existing between the molecules of the components in four binary liquid mixtures. The liquid mixtures contain cyclohexane (CH) as the common component and the second component varied are benzene (B), n-hexane (n-h), carbon tetrachloride (CTC) and p-xylene (p-x). In these binary systems the variation in the intermolecular attraction is mainly due to the second component. 2 Experimental Details The non-polar solvents cyclohexane (b.p: 80.72), benzene (b.p: 80.1), n-hexane (b.p: 68.7), carbon tetrachloride (b.p: 76.8) and p-xylene (b.p: 138.3) were of AnalaR grade samples and these were purified by usual methods 12, 13 and their boiling points agreed with the literature values indicating that the liquids used in the present study are of high purity. The mixtures were prepared by mixing appropriate weight of the two components in these four systems and the mole fractions were calculated from the number of moles. The ultrasonic velocities (U) of the above liquids and their mixtures were measured using multi-frequency ultrasonic interferometer at a frequency of 2MHz (Mittal Enterprises-Model F-81). The accuracy in the measurement of ultrasonic

2 816 INDIAN J PURE & APPL PHYS, VOL 44, NOVEMBER 2006 Table 1 Ultrasonic velocity, density and viscosity values for cyclohexane benzene, n-hexane, carbon tetrachloride and p-xylene systems at 298 K Ultrasonic velocity (U) ms -1 Density (ρ) kgm -3 Viscosity (η) / 10-3 Nsm Fig. 1 Plots of ultrasonic velocity versus molefraction of cyclohexane with hydrocarbons at 298 K velocity was within ±0.01ms -1. The densities (ρ) of these solutions were measured using 10ml specific gravity bottles in an electronic balance precisely within ±0.1mg accuracy. Oswald s viscometer was used to measure the viscosities (η) of the solutions. The temperature was maintained constant at 298 K using proportional temperature controller (accuracy ±0.1 C) during the measurement of ultrasonic velocity, density and viscosity values. Acoustical parameters such as adiabatic compressibility (β), free volume (V f ), internal pressure (π i ), intermolecular free length (L f ), Rao constant (R), cohesive energy (CE), Available volume (v a ) and the molecular interaction parameters (χ) were calculated using standard equations Results and Discussion The measured values of ultrasonic velocity along with densities and viscosities for all the four systems are given in Table 1. The plots of ultrasonic velocity against mole fraction of cyclohexane at 298K are shown in Fig 1. These plots are almost linear with either positive or negative slope indicating the existence of very weak intermolecular attractions in these systems and there is little deviation from ideal behaviour. These forces may be of induced dipoleinduced dipole type. It may be pointed out that in systems containing cyclohexane and aromatic hydrocarbons, ultrasonic velocity decreases with increase in the mole fraction of cyclohexane unlike in aliphatic systems where the trend is reverse. This is because the ultrasonic velocity of aromatic hydrocarbon is greater than that of aliphatic compounds of comparable molecular mass. Similarly, the trend in ultrasonic velocity suggests that the cyclohexane-p-xylene interaction is stronger than cyclohexane-benzene. This may be probably due to the larger size of p-xylene and hence greater polarisability of the molecule. The cyclohexanecarbon tetrachloride interaction is stronger than cyclohexane n-hexane interactions. This may be due to the presence of electronegative chloro group. Adiabatic compressibility (β), intermolecular free length and internal pressure values are calculated for four systems investigated and the values are presented in Table 2. Since adiabatic compressibility is inversely proportional to u 2, the trend in adiabatic compressibility with concentration is the reverse of the trend in ultrasonic velocity with concentrations in all the four systems. Further, the plots of adiabatic compressibility versus mole fraction of cyclohexane are almost linear suggesting that these systems are close to ideal ones. The variations in adiabatic compressibility values with concentration indicate that the strength of induced dipole induced dipole interactions is concentration dependent and generally

3 KANNAPPAN & SANTHI: ULTRASONIC INVESTIGATION OF BINARY LIQUID MIXTURES 817 Table 2 diabatic compressibility and linear free length and internal pressure values for cyclohexane benzene, n-hexane, carbontetrachloride and p-xylene systems at 298 K Adiabatic compressibility (β)/ m 2 N -1 Linear free length (L f ) Å Internal pressure (Πi) atm the interactions are very weak in dilute solutions and relatively strong in concentrated solutions. In the case of cyclohexane-benzene and cyclohexane-p-xylene systems, the linear free length decreases when benzene or p-xylene is added to cyclohexane. This trend suggests the molecular interactions increase with increase in mole fraction of benzene or p-xylene. But in the case of the other two systems, the reverse trend is observed. The increase in free length in the case of cyclohexane-n-hexane system suggests that there is weak interaction between the components. In cyclohexane-carbon tetrachloride system, there is decrease in the free length with increase in mole fraction of carbon tetrachloride but the decrease is less than those observed in cyclohexane-benzene and cyclohexane-p-xylene. Thus, the interactions in cyclohexane-carbontetrachloride are stronger than the interaction in cyclohexane-n-hexane, but weaker than CH-B and CH-p.-X. The intermolecular free length (L f ) in binary liquid mixtures can be used to assess the attraction between the component molecules. The values of intermolecular free length in a binary mixture depend on concentration and temperature. At a given concentration for binary systems intermolecular free length increases with increase in temperature. This may be due to the weakening of intermolecular attraction due to thermal agitation. At a given temperature, intermolecular free length either increases or decreases with concentration depending upon the components of the liquid mixture. The intermolecular free length values at a given temperature and concentration in different systems can be used to compare the induced dipole-induced dipole interactions in the four systems investigated. A intermolecular free length values are also concentration dependent indicating that the molecular interactions in these four systems are concentration dependent. In the case of CH-B, CH-p-X, the free length values are almost constant suggesting similar interactions between the components in these two systems. In CH- CTC a free length values are much greater than in CH-n-H system at any concentration indicating much weaker interactions in CH-n-H. A comparison of intermolecular free length values in this way suggests that the intermolecular attractions are in the order cyclohexane-p-xylene cyclohexanebenzene > cyclohexane-carbontetrachloride > cyclohexane-n-hexane. Thus, the dispersion interaction correlates with dielectric constant of the components. The dielectric constants of cyclohexane, p-xylene, benzene, carbon tetrachloride and n-hexane are 2.02, 2.27, 2,28, 2.24 and 1.89 respectively 18. The internal pressure (π i ) in binary mixtures can be used to access the intermolecular attraction between the components. These values are given for the four systems in Table 2. The internal pressure values are less in mixture containing aromatic hydrocarbons while they are greater in the case of pure components for systems with aliphatic components suggesting the presence of weak induced dipole-induced dipole molecular interaction. The change in the internal pressure value is significant in mixtures containing equimolar components. Thus, these types of molecular interactions are the strongest in mixtures with mole fraction of the component is about 0.5. The free volume (V f ) and available volume (V a ) values are also calculated for the four binary systems (Table 3). It is found that for a given system at a given temperature, free volume increases with concentration while available volume decreases except cyclohexane p-xylene system.

4 818 INDIAN J PURE & APPL PHYS, VOL 44, NOVEMBER 2006 Table 3 Rao constant, free volume and available volume values for cyclohexane benzene, n-hexane, carbontetrachloride and p-xylene systems at 298 K Rao constant (R) / 10-4 Free volume V f / 10-7 m 3 Available volume Va / 10-5 m Table 4 Cohesive energy and molecular interaction parameter values for cyclohexane benzene, n-hexane, carbontetrachloride and p- xylene systems at 298 K Cohesive energy (CE) kjmol -1 Molecular interaction parameter (χ) 10-2 (X 1 ) CH-B CH-n-H CH-CTC CH-P-X CH-B CH-n-H CH-CTC CH-P-X Fig. 2 Plots of molecular interaction parameter versus molefraction of cyclohexane with hydrocarbons at 298 K Cohesive energy (CE) in a liquid is an indicative of the attractive force existing between the molecules. When two liquids are mixed, the cohesive energy decreases if there are molecular attraction and in all the four systems the cohesive energy of the mixture is less than that of pure cyclohexane. Of course the change in cohesive energy is less. The values of cohesive energy are given in Table 4. The trend in cohesive energy also suggests that the weak induced dipole-induced dipole interactions are stronger in binary systems containing aromatic liquids than mixture containing aliphatic compounds. This may be due to greater polarizability of aromatic hydrocarbons than those of aliphatic compounds. The molecular interaction parameters with respect to velocity (χ U ) are negative for the mixtures indicating the presence of attractive force due to induced dipole in four binary mixtures. Further, molecular interaction values are more negative for binary mixtures with compositions X 1 = 0.5. This also suggests that the induced dipole-induced dipole attractive forces are the strongest for this composition (Table 4 and Fig.2). Generally, induced dipoleinduced dipole interactions are almost weak and this is indicated by the almost linear variation of Rao Constant (Table 3) with concentrations in all the four binary mixtures. 4 Conclusion There are weak induced dipole-induced dipole interactions in binary mixtures including cyclohexane

5 KANNAPPAN & SANTHI: ULTRASONIC INVESTIGATION OF BINARY LIQUID MIXTURES 819 and benzene, n-hexane, carbontetrachloride in p- xylene. These interactions are significant at concentration above 0.5 mole fraction. The strength of the interactions is in the order p-xylene-cyclohexane benzene cyclohexane > carbon tetrachloride cyclohexane > n-hexane cyclohexane. Thus, the interactions correlate with the polarizability of the molecules of the components in the mixture. References 1 Ali A, Nain A K Chand D & Lal B, Indian J Chem, 44A (2005) Seetharaman V, Kalyanasundaram S & Gopalan A, Indian J Pure & Appl Phys, 42 (2004) Acharya S, Dash S K & Swain B B, Acoust Lett, 21(3) (1997) Kannappan V & Jaya Santhi R, Indian J Pure & Appl Phys, 43 (2005) Mishra P.K, Dash A, Behera B, Swain B.B & Chakravorthy V, Acoust Lett, 19 (1995) Kannappan V, Xaxier Jesu Raja S & Jaya Santhi R, Indian J Pure & Appl Phys, 41 (2003) Nikam P S, Mehdi Hasan Pqwar T B & Sawant A.B, Indian J Pure & Appl Phys, 42 (2004) Yadava S S & Aniruddh Yadav, Indian J Pure& Appl Phys, 42 (2004) Kannappan V & Jaya Santhi R, J Acous Soc Ind, 29 (2001) Kannappan V, Jaya Santhi R & Malar E JP, Phys & Chem Liq, 40 (2002) Kannappan V, Jaya Santhi R & Xavier Jesu Raja S, Phys & Chem Liq, 14 (2003) Suryananarayanan C V & Kuppusamy J, J Acous Soc Ind, 4 (1976) Suryanarayanan C V, Indian J Chem, 25A (1986) Tiwari K, Patra C & Chakaravorthy A, Acoust lett, 19(3), 1995), Ramanjappa T, Murahari Rao E & Rajagopal E, Indian J Pure & Appl Phys, 31 (1993) Subramanyan Naidu P & Ravindra Prasad K, Indian J Pure & Appl Phys, 42 (2004) Ezhil Pavai R, Vasantharani P & Kannappan A N, Indian J Pure & Appl Phys, 42 (2004) Robert C Weust, CRC Handbook of chemistry & physics 52 nd Edition (The Chemical Rubber Co) 1971.

Journal of Chemical and Pharmaceutical Research, 2012, 4(1): Research Article

Available online www.jocpr.com Journal of Chemical and Pharmaceutical Research, 2012, 4(1):170-174 Research Article ISSN : 0975-7384 CODEN(USA) : JCPRC5 Acoustical studies on ternary mixture of toluene