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Journal of Molecular Liqu

Thermodynamic and transport behaviour of binary liquid mixtures of benzyl

alcohol with monocyclic aromatics at 303.15 K

A. Ali *, M. Tariq

Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi, 110025, India

Received 25 April 2005; accepted 20 September 2005

Available online 5 July 2006

Abstract

This paper presents densities, q, ultrasonic speeds, u, viscosities, g, and refractive indices, n, of pure benzyl alcohol (BA), benzene (B),

chlorobenzene (CB), benzonitrile (BN), nitrobenzene (NB), and their binary liquid mixtures, with BA as a common component, over the whole

composition range at 303.15 K. The excess molar volumes, VE, deviations in isentropic compressibility, Dks, viscosity, Dg, ultrasonic speed, Du,and in refractive index, Dn, were calculated from the experimental data. The apparent molar volumes, Vf,2, and apparent molar isentropic

compressibilities, Kf,2, of B, CB, BN and NB in BA were also calculated. The values of Vf,2 and Kf,2 were used to estimate the partial molar

volumes, V0f,2, and partial molar isentropic compressibilities, K0

f,2, of B, CB, BN and NB in BA at infinite dilution. The variations of these

parameters with composition of the mixtures suggest that the interaction between BA and B/CB/BN/NB molecules follow the sequence:

B<CB<BN<NB. Apart from using density data for the calculation of VE, excess molar volumes have also been estimated by using Flory’s

statistical theory. The results show that Flory’s theory predicts VE well for the mixture with least interaction between the component molecules

while it shows large deviation for the mixture showing highest interaction.

D 2006 Published by Elsevier B.V.

Keywords: Density; Ultrasonic speed; Viscosity; Refractive index; Excess molar volume; Binary mixtures; Interactions

1. Introduction

The present work is a continuation of our research program

[1–3] on thermodynamic and transport behaviour of binary

liquid mixtures of industrially important components. A

thorough knowledge of thermodynamic and transport proper-

ties of binary liquid systems is essential in many industrial

applications such as design calculation, heat transfer, mass

transfer, fluid flow, and so forth [4]. Benzyl alcohol was chosen

as solvent for the present study because its properties were the

subject of considerable interest, due to the versatility of this

compound as a solvent for gelatin, cellulose acetate, and

shellac and for pharmaceutical aid as an antimicrobial agent

[5]. Benzyl alcohol is also used in perfumery, in microscopy as

an embedding material, and in veterinary applications [6].

Benzene, chlorobenzene, benzonitrile, and nitrobenzene are

also well-known organic solvents used in many industrial and

biological processes. This study also aims to understand the

0167-7322/$ - see front matter D 2006 Published by Elsevier B.V.

doi:10.1016/j.molliq.2005.09.002

* Corresponding author. Tel.: +91 11 26981717x3257.

E-mail address: anwar_ ch@jmi.ernet.in (A. Ali).

intermolecular interactions, particularly the (k. . .H) bonding

between the molecules of aromatic alcohol and monocyclic

aromatics with different functional groups. Benzyl alcohol is

protic and exists in associated form whereas benzene,

chlorobenzene, benzonitrile, and nitrobenzene are aprotic

and, thus, exhibit no hydrogen bonding. Among the aromatics

benzene molecules are non-polar, while those of chloroben-

zene, benzonitrile and nitrobenzene are weakly polar, polar and

highly polar, respectively [7].

In order to investigate the nature of interactions we have

measured the densities, q, ultrasonic speeds, u, viscosities, g,and refractive indices, n, of the binary mixtures of BA with B,

CB, BN and NB, including those of the pure liquids, at 303.15 K

covering the entire composition range expressed by the mole

fraction x1 of BA. From the experimental values of q, u, g, and n,excess molar volumes, VE, deviations in isentropic compressi-

bilities, Dks, viscosities, Dg, ultrasonic speeds, Du, and in

refractive indices, Dn, partial molar volumes, V 0f,2, and partial

molar isentropic compressibilities, K 0f,2, of the monocyclic

aromatics in BA at infinite dilution have been calculated. These

functions offer a convenient model-free approach for the study

ids 128 (2006) 50 – 55

www.elsev

A. Ali, M. Tariq / Journal of Molecular Liquids 128 (2006) 50–55 51

of thermodynamic and transport properties of liquids and liquid

mixtures [8], not easily obtained by other means.

It is equally useful to carry out the theoretical analysis of the

experimental data in order to ascertain the suitability of

different theories and models of liquids and their mixtures. In

the recent years thermodynamic and transport properties of

liquid mixtures have been successfully estimated [9,10] with

the help of Flory’s statistical theory [11]. In the present study

the excess molar volumes have been computed by using

Flory’s theory.

2. Experimental

The chemicals (AR grade) employed were supplied by

Merck and S.D. Fine Chemicals Ltd. India. The purities of

the chemicals were �99%. All the chemicals were used

without further purification other than drying with molecular

sieves (Sigma Union Carbide 0.4 nm) to eliminate the

residual traces of water, if any, and were degassed right

before the measurements. The solutions were prepared by

mass using a Precisa XB-220A (Swiss make) electronic

balance with a precision of T0.1 mg. The precision of the

mole fraction is estimated to be better than 10�4. The

solutions were stored in special airtight bottles to prevent

contamination and evaporation.

The densities of pure liquids and their binary mixtures were

measured pycnometrically by the method described in our

earlier works [1–3]. The ultrasonic speeds were measured

using a single crystal variable path ultrasonic interferometer

operating at 3 MHz as described in the literature [1–3]. The

viscosity measurements were done using an Ubbelohde-type

suspended level viscometer. The viscometer containing the test

liquid was allowed to stand for about 30 min in a thermostated

water bath so that thermal fluctuation in the viscometer was

minimized. The temperature of the samples was maintained at

303.15T0.02 K in an electronically controlled thermostatic

water bath (JULABO, Germany).

Furthermore the accuracies of the density, ultrasonic speed,

viscosity and refractive index measurements were ascertained

by comparing the experimental values for pure liquids with the

corresponding literature values at 303.15 K (Table 1).

3. Results and discussion

Excess properties describe the deviation of a solution from

the ideal behaviour, and can provide insight into effects such

Table 1

Comparison of experimental density, viscosity, ultrasonic speed, and refractive inde

Component q (kg m�3) u (m s�1)

Expt. Lit. Expt. Lit.

Benzyl alcohol 1037.1 1037.0a 1516.6 1510

Benzene 868.6 868.2e 1281.5 1281

Chlorobenzene 1094.9 1095.0a 1252.2 1252

Benzonitrile 996.5 996.4c 1403.9 1402

Nitrobenzene 1194.2 1193.4b 1447.5 1444

aRef. [12], bRef. [13], cRef. [14], dRef. [15], eRef. [16], fRef. [17], gRef. [18], hRef

as: (i) difference in shape and size of the component molecules,

(ii) reorientation of the component molecules in the mixture,

and (iii) molecular interactions between them. Excess molar

volumes, VE, deviations in isentropic compressibilities, Dks,

viscosities, Dg, ultrasonic speeds, Du, and refractive indices,

Dn, were evaluated from the experimental measurements of q,g, u, and n (Table 2) at 303.15 K, using the relations given

elsewhere [20–22].

The properties YE (VE,Dks,Dg,Du and Dn) of the mixtures

were fitted according to the Redlich–Kister [23] polynomials:

YE ¼ x1x2X5i¼1

Ai 1� 2x1ð Þi�1 ð1Þ

where x1 and x2 are the mole fractions of BA and monocyclic

aromatics. The Ai fitting coefficients were evaluated by least-

squares method and the corresponding standard deviations, r(YE), were calculated using the relation:

r YE� �

¼X

YEexpt � YE

cal

� �2= m� nð Þ

�� 1=2

ð2Þ

where m is the number of experimental data points and n is the

number of coefficients considered (n =5 in the present

calculation), and are listed in Table 3. The variations of the

smoothed values of VE, Dks, Dg, Du, and Dn, using Eq. (1),

with mole fraction x1 of BA at 303.15 K, are shown graphically

in Figs. 1–5 and have been qualitatively examined by

considering the effects, which influence these parameters.

A qualitative interpretation of the behaviour of the above

parameters with composition may be proposed. Mixing of the

liquid components into each other will induce (i) the disruption

of hydrogen bonds in BA and loss of dipolar association in CB,

BN and NB molecules which would be maximum in CB and

minimum in NB and (ii) the formation of weak to medium-

strength hydrogen bonds between k-electrons of aromatic rings

(B, CB, and BN molecules) and H-atom of the BA molecule,

somewhat stronger hydrogen bond between nitrogen atom of

NB (with its lone pair of electrons) and H-atom of the BA

molecule, and dipole–dipole interaction between unlike

molecules. Also, the interaction of the type k. . .k (between

k-electrons of BA and B/CB/BN/NB molecules) may also be

present in these mixtures. The first effect (i) leads to an

expansion in volume, resulting in positive VE and Dks values or

negative Du and Dn values. Positive values in VE and Dks, and

opposite trend in Du and Dn, may also occur when component

x of pure liquids with literature data at 303.15 K

g (10�3 Nm�2 s) n

Expt. Lit. Expt. Lit.

.8f 4.5250 4.5150a 1.5352 1.5354a

.7e 0.5645 0.5680e 1.4948 1.4948h

.0f 0.7098 0.7155a 1.5191 1.5195a

.7d 1.1238 1.1260c 1.5192 1.5189g

.3f 1.6461 1.6262b 1.5420 –

. [19].

Table 2

Experimental values of density, q, ultrasonic speed, u, viscosity, g, and

refractive index, n, as a function of mole fraction, x1, of benzyl alcohol for the

binary mixtures at 303.15 K

x1 q (kg m�3) u (m s�1) g (10�3 Nm�2 s) n

Benzyl alcohol +benzene

0.0000 868.6 1281.5 0.5645 1.4948

0.1079 889.7 1305.1 0.8732 1.5003

0.2167 910.5 1330.3 1.0305 1.5062

0.3472 934.5 1362.6 1.2915 1.5128

0.4657 955.6 1392.6 1.6010 1.5183

0.5516 970.4 1413.9 1.8773 1.5221

0.6577 987.7 1439.5 2.3059 1.5263

0.7244 997.9 1455.1 2.6529 1.5285

0.8680 1018.9 1487.5 3.5939 1.5328

0.9178 1025.9 1498.6 3.9835 1.5338

1.0000 1037.1 1516.6 4.5250 1.5352

Benzyl alcohol +chlorobenzene

0.0000 1094.9 1252.2 0.7098 1.5191

0.1372 1087.9 1294.2 0.9498 1.5218

0.2844 1081.2 1337.9 1.1576 1.5249

0.3371 1078.8 1353.6 1.2598 1.5261

0.4255 1074.6 1379.1 1.4588 1.5281

0.5741 1066.8 1421.6 1.9074 1.5307

0.6507 1061.9 1441.9 2.2118 1.5316

0.7556 1054.5 1466.8 2.7130 1.5326

0.8031 1051.1 1477.6 2.9823 1.5331

0.9053 1043.7 1498.7 3.6616 1.5342

1.0000 1037.1 1516.6 4.5250 1.5352

Benzyl alcohol +benzonitrile

0.0000 996.5 1403.9 1.1238 1.5192

0.1460 1005.7 1438.9 1.1228 1.5218

0.2760 1012.8 1462.7 1.2630 1.5246

0.3251 1015.3 1471.1 1.3659 1.5257

0.4147 1019.3 1485.9 1.5352 1.5276

0.5549 1025.2 1504.8 1.9016 1.5302

0.6387 1028.2 1512.9 2.1844 1.5314

0.7443 1031.3 1514.8 2.6347 1.5324

0.8022 1032.8 1515.9 2.9422 1.5329

0.9039 1035.2 1515.4 3.5949 1.5338

1.0000 1037.1 1516.6 4.5250 1.5352

Benzyl alcohol +nitrobenzene

0.0000 1194.2 1447.5 1.6461 1.5420

0.1725 1173.1 1488.9 1.2916 1.5412

0.2352 1164.2 1500.6 1.2923 1.5410

0.3083 1153.6 1511.9 1.3893 1.5407

0.4517 1132.5 1529.9 1.6568 1.5401

0.5919 1110.5 1538.6 2.0148 1.5394

0.6592 1099.3 1539.1 2.2341 1.5389

0.7706 1080.1 1538.6 2.6580 1.5375

0.8314 1069.5 1535.6 2.9556 1.5367

0.9106 1055.1 1530.2 3.4862 1.5359

1.0000 1037.1 1516.6 4.5250 1.5352

A. Ali, M. Tariq / Journal of Molecular Liquids 128 (2006) 50–5552

molecules interact less strongly. The second effect (ii)

contributes to the contraction in volume, thereby, making VE

and Dks values negative, and those of Du and Dn positive. It is

clear from Figs. 1 and 2 that for binary mixtures investigated

the values of VE and Dks become more negative as we move

from benzene to nitrobenzene. This suggests that the combined

effect (ii) of interaction of BA with B, CB, BN and NB

molecules exceeds the structure-breaking effect (i) in the

component molecules. Further, the extent of negative deviation

in these binary mixtures suggests that the strength of

interaction between unlike molecules should follow the order:

B<CB<BN<NB. Our finding is in good agreement with the

view proposed by Fort and Moore [24], according to which VE

and Dks become increasingly negative with increasing strength

of interaction between unlike molecules in the liquid mixtures.

Fig. 3 shows that Dg values are entirely negative for all the

four binary systems (BA+B/CB/BN/NB) and these negative

values follow the sequence: B<CB<BN<NB over the

complete composition range. Negative deviations occur where

dispersion and dipole–dipole forces are operative in the

system [25,26], but they may also occur where the components

are known to interact more strongly [24]. Similar conclusion

regarding Dg was also drawn by Prasad et al. [26] for

mixtures of anisole or methyl-tert-butyl ether with monocyclic

aromatics.

The extent of positive deviations in Du (Fig. 4) over the

entire composition range for all the four systems studied

suggests that significant interactions are operative in these

mixtures [27], and these interactions are in the order:

B<CB<BN<NB, this again reinforces our view regarding

the interaction between BA and B/CB/BN/NB molecules.

Similar trends in Du have also been reported for dimethylsul-

phoxide+N, N dimethylformamide/N, N dimethylacetamide

[28] binary mixtures.

The curves in Fig. 5 show that for all the systems under

study the deviations in refractive indices, Dn, are positive and

tend to become less positive on going from benzene to

nitrobenzene over the complete composition range. In general,

the magnitude of Dn decreases as the strength of interaction

between the component molecules in the mixture increases

[29], as in the present case.

The extent of interaction between the component molecules

in a mixture is well reflected in the parameters like apparent

molar volume, apparent molar compressibility, partial molar

volume and partial molar compressibility [30,31]. The apparent

molar volumes, Vf,2, of B, CB, BN, and NB in BA were

calculated by using the equation [30]:

Vf;2 ¼ V42 þ V E=x2� �

ð3Þ

where V 2* is the molar volume of B/CB/BN/NB. The partial

molar volumes, Vf,20 , of B, CB, BN, and NB in BA at infinite

dilution were obtained by using the method described by others

[31,32].The deviations in Vf,2 at infinite dilution, DV, were

calculated by using the equation [31]:

DV ¼ V 0f;2 � V 4

2 ð4Þ

The values of Vf,20 , V 2* and DV are listed in Table 4. It is clear

from Table 4 that the values of DV are negative (i.e., the partial

molar volume, Vf,20 , of B/CB/BN/NB in BA at infinite dilution

are smaller than their corresponding molar volumes in the pure

state, V 2*), and become more so in the sequence: B<CB<

BN<NB. Thus, as also suggested by VE values, the strength of

interaction between unlike molecules in the mixtures increases

as we move from benzene to nitrobenzene.

Table 3

Coefficients Ai of Eq. (1) and standard deviations r ( YE) for the binary mixtures at 303.15 K

Property A1 A2 A3 A4 A5 r ( YE)

Benzyl alcohol +benzene

VE (10�7 m3 mol�1) �10.3532 8.5147 7.5788 �5.6932 �6.0709 0.0243

Dks (10�11 m2 N�1) �8.0128 0.6942 2.7561 �0.6451 �1.7248 0.0026

Dg (10�3 Nm�2 s) �3.3650 1.6443 �0.0775 �0.6332 3.1265 0.0025

Dn (10�2) 13.6856 �7.2600 �2.9120 �2.5920 1.2847 0.0611

Du (m s�1) 8.4051 �29.0139 �23.6776 10.1374 14.9345 0.0357

Benzyl alcohol +chlorobenzene

VE (10�7 m3 mol�1) �19.9869 8.6246 21.9870 �7.1648 �12.169 0.0509

Dks (10�11 m2 N�1) �9.7941 1.1340 1.5515 �1.9973 �1.3974 0.0153

Dg (10�3 Nm�2 s) �3.8314 1.4771 0.1142 1.2199 �0.5870 0.0008

Dn (10�2) 9.3523 �2.8762 �17.2273 3.0089 16.5358 0.0114

Du (m s�1) 66.2122 �38.5092 �5.4261 27.1753 9.3842 0.1975

Benzyl alcohol +benzonitrile

VE (10�7 m3 mol�1) �25.0084 �1.0444 0.0340 �2.5257 �0.2892 0.0539

Dks (10�11 m2 N�1) �11.5183 0.5554 3.4270 �6.0086 �4.0480 0.0347

Dg (10�3 Nm�2 s) �4.3353 1.3146 �0.9338 0.6666 �1.3916 0.0065

Dn (10�2) 8.2848 �3.8567 �12.2474 5.5634 2.3252 0.0217

Du (m s�1) 153.793 �33.4484 �65.8836 100.0788 62.8513 0.6073

Benzyl alcohol +nitrobenzene

VE (10�7 m3 mol�1) �36.6632 5.5544 6.2463 �6.4767 �36.023 0.0563

Dks (10�11 m2 N�1) �12.6676 0.3937 0.6673 0.6751 �5.9167 0.0208

Dg (10�3 Nm�2 s) �5.2983 0.5751 �2.4945 1.7346 �2.6304 0.0081

Dn (10�2) 5.7706 �3.1834 �8.3026 6.2955 4.2813 0.0246

Du (m s�1) 206.620 �2.8000 �19.8109 �15.9297 84.1171 0.4141

A. Ali, M. Tariq / Journal of Molecular Liquids 128 (2006) 50–55 53

The apparent molar compressibilities, Kf,2, of B, CB, BN,

and NB in BA were calculated using the relation [30]:

Kf;2 ¼ Kf;24 þ KEs =x2

� �ð5Þ

where KsE [= (ksV)

E] is the excess molar compressibility of

the mixture; x2 and K*f,2 are the mole fraction and molar

isentropic compressibility of B/CB/BN/NB, respectively. The

partial molar compressibilities, K0f,2, of B, CB, BN, and NB

in BA at infinite dilution were obtained by using the method

-12

-10

-8

-6

-4

-2

0

0 0.25 0.5 0.75 1x1

VE (

10-7

m3

mol

-1)

BCBBNNB

Fig. 1. Variation of excess molar volume with mole fraction x1 of benzyl

alcohol for the binary mixtures at 303.15 K.

described elsewhere [21,30,31]. The deviations in Kf,2 at

infinite dilution, DK, were obtained by using the relation

[30]:

DK ¼ K0f;2 � Kf;24 ð6Þ

The values of K0f,2, K*f,2 and DK are also included in Table

4. The partial molar compressibilities, K0f,2, of B, CB, BN,

and NB in BA, at infinite dilution, characterize the com-

-4

-2

0

0 0.25 0.5 0.75 1x1

Δks

(10-1

1 m

2 N-1

)

BCBBNNB

Fig. 2. Variation of deviation in isentropic compressibility with mole fraction x1of benzyl alcohol for the binary mixtures at 303.15 K.

-1.5

-1

-0.5

0

0 0.25 0.5 0.75 1x1

Δη(1

0-3 N

m-2

s)

B

CB

BN

NB

Fig. 3. Variation of deviation in viscosity with mole fraction x1 of benzyl

alcohol for the binary mixtures at 303.15 K.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 0.25 0.5 0.75 1x1

Δn (

10-3

)

B

CB

BN

NB

Fig. 5. Variation of deviation in refractive index with mole fraction x1 of benzy

alcohol for the binary mixtures at 303.15 K.

A. Ali, M. Tariq / Journal of Molecular Liquids 128 (2006) 50–5554

pressibilities of their molecules in the mixture, whereas

molar isentropic compressibilities, Kf,2* , of pure components

B/CB/BN/NB can be considered as partial molar isentropic

compressibilities of these aromatics when dissolved in itself.

It is worth mentioning that all the values of DK (Table 4)

for four binary mixtures studied are negative and the

negative values follow the order: B<BN<CB<NB. Negative

values of DK are indicative of significant interaction between

the component molecules in the mixture. This further supports

our earlier finding.

It is worth to mention that the variations of VE, Dks, Dg, Du,and Dn with composition of the mixtures investigated, together

Table 4

The values of V0f,2, V*2, DV, K

0f,2, K*2, and DK of monocyclic aromatics in BA

for the binary mixtures at 303.15 K

BA + V0f,2 V*2 DV

(10�5 m3 mol�1)

Benzene 8.8354 8.9926 �0.1573Chlorobenzene 1.0050 1.0280 �0.2308Benzonitrile 1.0040 1.0348 �0.3086Nitrobenzene 9.6772 1.0309 �0.6318

BA + K0f,2 K*2 DK

(10�14 m5 N�1 mol�1)

Benzene 5.2746 6.3042 �1.0296Chlorobenzene 4.5357 5.9881 �1.4524Benzonitrile 3.8838 5.2689 �1.3850Nitrobenzene 1.7664 4.1200 �2.3536

-5

15

35

55

0 0.25 0.5 0.75 1x1

Δu (

m s

-1)

B

CB

BN

NB

Fig. 4. Variation of deviation in ultrasonic speed with mole fraction x1 of benzyl

alcohol for the binary mixtures at 303.15 K.

l

with the values of DV and DK, truly support each other, and

they further suggest that the strength of interaction in these

binaries is in the order: B<CB<BN<NB.

In recent years [10,33], Flory’s statistical theory [11] has

been successfully used to estimate theoretically and then

analyse the excess thermodynamic functions of binary liquid

mixtures. In this paper, we have applied Flory’s theory in order

to predict the excess molar volume, VFE, for the present binary

liquid mixtures. According to Flory’s equation of state [11], VFE

is given as:

VEF ¼

X2i¼1

xiVi4

#"VV o7=3= 4=3ð Þ � VV o

� �1=3on ihTT � TT o� �

ð7Þ

The terms and notations used in the Eq. (7) are the same as

given in the literature [10,11].

The estimated values of VFE together with the experimental

values of VE for binary mixtures, BA+B and BA+NB, are

graphically shown in Fig. 6. It is evident (Fig. 6) that for the

mixture BA+B, which shows least interaction between BA and

-10

-8

-6

-4

-2

0

x1

BA+B

BA+NB

VE (

10-7

m3

mol

-1)

Fig. 6. Variation of experimental and theoretical values of excess molar volume

for the systems BA+B and BA+NB at 303.15 K. Hollow points show values

calculated using Flory’s theory and filled marks show experimental values.

A. Ali, M. Tariq / Journal of Molecular Liquids 128 (2006) 50–55 55

B molecules, both VE and VFE values show negative deviations

and closely support each other. On the other hand, for the

mixture BA+NB, which shows highest interaction between

BA and NB molecules, VE values show negative deviation

while VFE show no deviation. Thus, it is interesting to note that

Flory’s statistical theory, which is known to predict excess

molar volumes for mixtures containing non-polar or weakly

polar components well, fails when applied to mixtures con-

taining polar components [34], as in the present case.

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