Study of molecular interactions in binary liquid mixtures - NOPR

Indian Journal of Pure & Applied Physics Vol. 46, March 2008, pp. 169-175

Study of molecular interactions in binary liquid mixtures R Kumar#, S Jayakumar∗ & V Kannappan+ #

Department of Physics, The New College, Chennai 600 014

∗

Department of Physics, R K M Vivekananda College, Chennai 600 004 +

Department of Chemistry, Presidency College, Chennai 600 005 E-mail: [email protected]

Received 20 March 2006; revised 11 April 2007, accepted14 December 2007 The acoustical parameters for two binary liquid mixtures namely, acetone – carbon tetrachloride (CCl4) and acetone – benzene have been determined at three different temperatures. The acoustical parameters such as the adiabatic compressibility κ, the free length of interaction Lf, interaction parameter χ, Lennard Jones Potential (LJP) and also excess parameters such as excess velocity uE, excess compressibility κE, excess volume VfE and excess free length LfE are computed for the two systems at 303K, 308K and 313K from the measured ultrasonic velocity and density values. The extent of interactions existing between component molecules has been found out. In acetone – CCl4 system, the interaction parameter values have been out to be negative suggesting the presence of weak dipole –induced dipole interactions in this system. However, in acetone – benzene system, there are strong dipole - induced dipole interactions. With increase in temperature, the extent of interaction becomes weak in both the systems due to thermal agitation of the component molecules. Keywords: Binary mixtures, Free length of interaction, Dipole–induced dipole interaction

1 Introduction Ultrasonic velocity measurements have been employed extensively to detect and assess weak and strong molecular interactions in binary1,2 and ternary3,4 mixtures, because mixed solvents find practical applications in many chemical and industrial processes. To meet the needs of applications, ultrasonic velocity measurements are generally carried out at different temperatures. The parameters such as ultrasonic velocity (u), density (ρ) and viscosity (η) and computed parameters such as adiabatic compressibility (κ), free length (Lf), interaction parameter (χ), internal pressure (πi), acoustic impedance (Z) and Lennard Jones Potential (LJP) provide better insight into intermolecular interactions. The present investigation is carried out to study molecular interactions in the binary liquid mixtures of acetone – CCl4 and acetone – benzene in the temperature range 303 – 313K. 2

Materials and Methods High purity acetone, CCl4 and benzene (S.D. Fine Chem. Ltd.) are redistilled and purified by the

standard methods5. Binary mixtures are prepared by mixing appropriate volumes of the liquid components in the standard flasks with airtight caps and the mass measurements are performed on high precision digital balance with an accuracy of ±1 mg. The uncertainty in mole fraction is ±0.0001. The accuracy in the measurements of density and viscosity is of the order of ±0.01 and ±0.001, respectively. The required properties are measured for freshly prepared solutions. The ultrasonic velocity is measured with an uncertainty of ±0.3% using a single crystal ultrasonic interferometer (Mittal Enterprises, New Delhi) operating at 2 MHz (Model F81), which is calibrated with water and benzene. The temperature stability is maintained within 0.1 K by circulating thermostated water around the interferometer cell that contains the liquid, with a circulating pump. In order to minimize the error of measurements, several maxima of ultrasonic velocity are allowed to pass and their number n is counted. All maxima are recorded with highest swing of the needle on the micrometer scale of the interferometer. The total distance, d moved by the reflector of the interferometer cell is given by

INDIAN J PURE & APPL PHYS, VOL 46, MARCH 2008

170 d = nλ / 2

… (1)

where λ is wavelength of ultrasonic wave. The frequency of the interferometer crystal is accurately known (2 MHz) and using λ from Eq. (1), the ultrasonic velocity u m/s is calculated by the relation: u = νλ

… (2)

Employing the measured values of velocity (u), density (ρ) and viscosity (η), some acoustical and allied parameters can be computed through the following expressions6,7: Adiabatic (isentropic) compressibility; κ= 1/ u2ρ

… (3)

Acoustic impedance; Z = u ρ

… (4)

Free length; Lf = K κ1/2

… (5)

Internal pressure; πi = bRT (Kη/u) 1/2ρ2/3 / Meff … (6) where, Meff = x1 M1 + x2 M2; b is a constant (value , 2); K is temperature dependent constant. [value, (93.875 + 0.375 T) × 10-8]; R is universal gas constant. Interaction parameter;χ = (uexp2 / uideal2) – 1

… (7)

where, uideal = x1 u1 + x2 u2 is ideal mixing velocity. Lennard Jones Potential; (LJP) =(6*V / VA) – 13

… (8)

Excess parameters are computed using the relations: Excess velocity; uE = u – (x1u1 + x2u2)

… (9)

Excess compressibility;κ = κ - (x1κ1 + x2κ2) … (10) E

3

Results and Discussion Acetone contains carbonyl functional group, which is polar and hence it can interact with non-polar molecules like benzene and carbon tetra chloride through polar – induced dipolar interaction. In pure acetone there are dipole – dipole as well as the dispersive interactions. The effect of adding a nonpolar second component is primarily to disrupt the dipolar interactions of the first component. It can be seen from the plot (Fig.1) that the ultrasonic velocity decreases with increase in mole fraction of CCl4. This may be due to self-association of the solvent molecules and a very weak dipole – induced dipole interaction between the component molecules, which is concentration dependent8. Further, in this binary system the interaction becomes weak with increase in temperature due to thermal agitation of component molecules and this is indicated by the decrease in velocity values (Table 1). Kannappan et al.2 showed similar kind of interaction between an aliphatic ketone and hexane system. They also showed that the adiabatic compressibility exhibited a non-linear variation. Similar trend is observed in the case of acetone – CCl4 system (Fig.1). The interaction parameter (χ), free length of interaction (Lf) and internal pressure (πi) values (Table 1) also suggest that the interaction between the component molecules of acetone and CCl4 becomes weak and decreases both with increase in mole fraction of CCl4 as well as with temperature. The increase in the internal pressure with concentration of CCl4 and with temperature is attributed to the decreasing extent of interaction between the solute solvent molecules.

Fig. 1—Plot of ultrasonic velocity versus mole fraction of CCl4

KUMAR et al.: MOLECULAR INTERACTIONS IN BINARY LIQUID MIXTURES

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Table 1 — Computed values of acoustical parameters at different temperatures for acetone – Carbon tetra chloride Mole fraction xCCl4

Ultrasonic Density (ρ) Adiabatic Acoustic Free length Interaction (Lf) velocity (u) Kg/m3 compressibility (κ) impedance (Z) parameter χ m/s 10-10 N-1m2 106 Kg m-2s-1 A0

Lennard Jones Potential LJP J/mol

Internal pressure πi 105 pascal

At 303K 0.0000 0.1590 0.3354 0.5317 0.7516 1.0000

1148.2 1073.6 1008.0 960.3 924.0 906.0

777.80 957.60 1090.40 1265.50 1420.90 1559.70

9.752 9.060 9.026 8.569 8.243 7.811

0.893 1.03 1.10 1.22 1.31 1.41

0.6246 0.602 0.6009 0.5855 0.5742 0.559

0.0000 -0.0640 -0.1075 -0.1126 -0.0854 0.0000

8.248 5.237 3.216 2.007 1.201 0.833

1.373 0.667 0.939 1.41 2.2 1.234

At 308K 0.0000 0.1590 0.3354 0.5317 0.7516 1.0000

1121.8 1055.3 996.5 949.8 915.5 892.7

772.1 940.17 1085.14 1258.2 1406.8 1544

10.291 9.551 9.28 8.81 8.481 8.127

0.866 0.992 1.08 1.20 1.29 1.38

0.6416 0.6181 0.6093 0.5936 0.5824 0.5702

0.0000 -0.0548 -0.0909 -0.0981 -0.0707 0.0000

7.077 4.625 2.907 1.765 1.025 0.573

1.476 0.694 0.989 1.496 2.309 1.303

At 313K 0.0000 0.1590 0.3354 0.5317 0.7516 1.0000

1101.4 1039.2 980.6 933.2 900.0 877.8

771.9 927.5 1077.1 1255.96 1393.4 1517.7

10.679 9.984 9.655 9.143 8.86 8.55

0.850 0.964 1.06 1.17 1.25 1.33

0.6536 0.6319 0.6215 0.6047 0.5953 0.5848

0.0000 -0.0504 -0.0890 -0.0999 -0.0718 0.0000

6.255 4.118 2.499 1.397 0.714 0.293

1.574 0.729 1.043 1.571 2.409 1.367

Fig. 2—Plot of ultrasonic velocity versus mole fraction of C6H6

In acetone – benzene system the ultrasonic velocity increases with increase in concentration of benzene. This indicates that there is a dipole – induced dipole interaction between component molecules. Further, increase in temperature decreases the interaction due to thermal agitation, which is obvious from the decrease in ultrasonic velocity at higher temperatures. Similar observations were made by Syal et al.10 and Subramaniyam Naidu & Ravindra Prasad11 in the

investigation of temperature dependence of ultrasonic velocity in certain binary liquid mixtures. The free length of interaction Lf decreases with increase in the mole fraction of benzene which shows that the dipole – induced dipole interaction becomes stronger which makes the system less compressible as evident from the values of adiabatic compressibility. The induced dipole – dipole interaction is confirmed by the nonlinear variation of ultrasonic velocity in the binary

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INDIAN J PURE & APPL PHYS, VOL 46, MARCH 2008

Fig. 3— Plot of adiabatic compressibility versus mole fraction of CCl4

Fig. 4— Plot of adiabatic compressibility versus mole fraction of benzene

liquid mixtures of non-polar compound P-Xylene with polar liquids such as pyridine, chlorobenzene, bromobenzene and nitrobenzene9. The increase in the values of Lf and κ with increase in temperatures clearly reveals that the interaction becomes weaker at high temperatures. The trend in other parameters such as LJP, internal pressure πi and interaction parameter χ also supports the increase in dipole – induced dipole interaction with mole fraction of benzene and decreasing trend with temperature. The internal pressure shows similar trend as in the case of acetone – CCl4 system. But in acetone – benzene system the extent of interaction is comparatively more. The extent of dipole – induced dipole interaction depends on the polarizability of the interacting molecules. Benzene molecule, being larger molecule than CCl4 is more polarizable. Therefore, the interactions are stronger in acetone – benzene system than in acetone CCl4 system.

Excess Thermodynamic Parameters

The excess parameters such as excess velocity uE, excess compressibility κE, excess free volume VfE and excess free length LfE for the two systems are plotted in Figs 5-8. The excess velocity shows a slight negative deviation in acetone – CCl4 mixture and relatively large positive deviation in acetone – benzene mixture suggesting the presence of weak and strong dipole – induced dipole interactions in the two systems respectively. At higher temperatures, the increasing negative value and decreasing positive values of excess velocity for the two systems indicate the weakening of interactions. The values of κE changes sign from positive to negative in acetone – CCl4 at 303K and show positive deviation at high temperatures. For acetone – benzene it shows negative deviation at 303K and changes sign from positive to negative at high temperatures. The behaviour of the two systems can be explained as

KUMAR et al.: MOLECULAR INTERACTIONS IN BINARY LIQUID MIXTURES

Fig. 5—Plot of excess velocity versus mole fraction of CCl4/ benzene

Fig. 6—Plot of excess compressibility versus mole fraction of CCl4/ C6H6

Fig. 7—Plot of excess volume versus mole fraction of CCl4/ C6H6

Fig. 8—Plot of excess free length versus mole fraction of CCl4/ C6H6

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Table 2 — Computed values of acoustical parameters at different temperatures for acetone – benzene Mole fraction xC6H6

Ultrasonic Density (ρ) Adiabatic Acoustic Free length Interaction (Lf) velocity (u) Kg/m3 Compressibility (κ) impedance (Z) parameter χ m/s 10-10 N-1m2 106 Kg m-2s-1 A0

Lennard Jones Potential LJP J/mol

Internal pressure πi 105 pascal

At 303K 0.0000 0.1712 0.3553 0.5536 0.7678 1.0000

1148.2 1164.4 1193.0 1221.4 1245.6 1278.0

779.36 792.01 811.97 827.14 844.11 864.67

9.733 9.312 8.653 8.104 7.636 7.081

0.895 0.922 0.969 1.01 1.05 1.11

0.6239 0.6103 0.588 0.5693 0.5527 0.5322

0.0000 -0.0103 -0.0021 0.0023 -0.0036 0.0000

8.248 9.0386 10.59 12.36 14.088 16.814

1.373 1.068 1.185 1.308 1.469 1.202

At 308K 0.0000 0.1712 0.3553 0.5536 0.7678 1.0000

1121.8 1154.6 1180.9 1209.1 1233.2 1254.8

772.1 788.03 802.59 823.52 833.49 860.61

10.291 9.5191 8.9347 8.3062 7.8892 7.3798

0.866 0.910 0.948 0.996 1.03 1.08

0.6416 0.6171 0.5978 0.5764 0.5618 0.5433

0.0000 0.0175 0.0202 0.0228 0.0151 0.0000

7.077 8.554 9.906 11.558 13.172 14.81

1.476 1.139 1.236 1.381 1.562 1.306

At 313K 0.0000 0.1712 0.3553 0.5536 0.7678 1.0000

1101.4 1134.3 1162.3 1189.4 1214.2 1233.2

771.9 779.47 798.59 821.5 836.04 856.36

10.679 9.971 9.269 8.604 8.114 7.679

0.850 0.884 0.928 0.977 1.02 1.06

0.6536 0.6315 0.6089 0.5867 0.5697 0.5542

0.0000 0.0185 0.0248 0.0259 0.0194 0.0000

6.255 7.615 8.934 10.383 11.881 13.172

1.562 1.18 1.287 1.463 1.674 1.392

follows. Mixing of acetone with CCl4 will induce the breaking up of the associated clusters of acetone releasing several dipoles, which in turn, can induce a dipole moment in CCl4 molecules, resulting dipole – induced dipole interaction. Thus, CCl4 acts as a structure breaker for acetone. This is also suggested by the complex trend in πi values with concentration in both the systems (Tables 1 - 2). The breaking up of associated structure of acetone leads to an expansion in volume, hence, an increase in κE and the dipole – induced dipole interaction is responsible for contraction in volume, hence, a decrease in κE. With increase in temperature the interaction becomes weak and the breaking of associated structure of acetone dominates, hence, increase in βE. The small negative values of κE and LfE for the acetone - benzene system in the entire range of mole fraction indicate that the effect of dipole – induced dipole interaction dominates over the breaking up of associated structure of acetone. Ali et al.12, 13 made similar observations for benzyl alcohol with cyclohexane and toluene. Ali and Nain14 also interpreted that κE and LfE become increasingly negative as the strength of interaction between component molecules increases. The structural changes in the component molecules of

Table 3 — Computed values of excess thermodynamic parameters at various temperatures for acetone – Carbon tetra chloride Mole fraction XCCl4

uE m/s

κE 10-11 N-1m2 VfE m3/mole

LfE 10-13 m

At 303K 0.1590

-36.090

3.815

0.0120

-12.51

0.3354

-58.966

-0.7337

0.0041

-1.999

0.5317

-59.122

-1.496

-0.0010

-4.455

0.7516

-42.162

-0.4876

-0.0039

-1.177

0.1590

-54.439

1.089

0.0099

3.570

0.3354

-70.611

1.798

0.0027

6.36

0.5317

-69.768

0.9054

-0.0019

3.692

0.7516

-50.715

1.882

-0.0043

7.019

0.1590

-71.096

5.372

0.0076

17.27

0.3354

-87.408

5.475

0.0014

18.31

0.5317

-87.385

4.149

-0.0025

14.51

0.7516

-67.010

5.614

-0.0046

19.69

At 308K

At 313K

KUMAR et al.: MOLECULAR INTERACTIONS IN BINARY LIQUID MIXTURES

Table 4 — Computed values of excess thermodynamic parameters at various temperatures for acetone – benzene uE m/s

κE 10-11 N-1m2

VfE m3/ mole

LfE 10-13 m

At 303K 0.1712 0.3553 0.5536 0.7678

57.665 130.894 207.322 283.361

-1.054 -4.081 -5.724 -6.249

0.0032 0.0018 0.0008 -0.0001

-3.374 -13.24 -19.13 -21.6

At 308K 0.1712 0.3553 0.5536 0.7678

47.962 118.899 195.127 271.082

1.020 -1.249 -3.687 -3.703

0.0016 0.0009 -0.0002 -0.0012

3.385 -3.691 -12.01 -12.54

At 313K 0.1712 0.3553 0.5536 0.7678

27.536 100.053 175.177 251.824

5.525 2.071 -0.73 -1.475

0.0008 0.0001 -0.0011 -0.0021

17.82 7.312 -1.846 -4.659

Mole fraction XC6H6

DMSO with acetone, 3-methoxyacetophenone and 4chloroacetophenone by the observed values of κE and LfE have been reported9, 15. 4

Conclusions The dependence of ultrasonic velocity and other derived parameters on composition of the mixtures and temperature is indicative of the presence of molecular interactions. The sign and extent of deviation of the excess functions from linear dependence on the composition of these mixtures and their variations with temperatures reveal that the extent of interaction decreases with increase in temperature. The interactions are primarily of dipole –

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induced dipole type of interactions which become stronger with mole fraction in acetone – benzene system and weaker in acetone – CCl4 system. Further, in both the systems the non polar CCl4 and benzene molecules behave as structure breaker for associated acetone. Acknowledgement The authors thank the management of R K M Vivekanada College and The New College for their keen interest shown in this work. References 1 Jayakumar S, Karunanithi N & Kannappan V, Indian J pure Appl Phys, 34 (1996) 761. 2 Kannappan V, Xavier Jesu Raja S & Jaya Santhi R, Indian J pure Appl Phys, 41 (2003) 690. 3 Ali A, Hyder S & Nain A K, Indian J Phys, 74B (1)(2000) 63. 4 Carter S, J Chem Soc, A 404 (1968). 5 Vogel A I, A textbook of practical Organic Chemistry, 5th Edn (John Willey, New York) 1989. 6 Subramaniyam Naidu P & Ravindra Prasad K, Indian J pure Appl Phys, 42 (2004)) 512. 7 Ezhil Pavai R, Vasantharani P & Kannappan A N, Indian J pure Appl Phys, 42 (2004) 934. 8 Dash S K, Chakaravorthy V & Swain B B, Acoust Lett, 19 (1996) 142. 9 Kannappan V & Jaya Santhi R, Indian J pure Appl Phys, 43 (2005) 750. 10 Syal V K, Chauhan S & Uma Kumari, Indian J pure Appl Phys, 43 (2005)) 844. 11 Subramaniyam Naidu P & Ravindra Prasad K, J pure Appl Ultrason, 27 (2005) 15. 12 Ali A,Yasmin A & Nain A K, Indian J pure Appl Phys, 40 (2002) 315. 13 Ali A, Hyder S & Nain A K, Indian J Phys, 74B (2000) 63. 14 Ali A, & Nain A.K, Bull Chem Soc (Japan). 15 Subramaniyam Naidu P, Prabhakara Rao & Ravindra Prasad K, J Pure Appl Ultrason, 24 (2002) 36.