Indian Journal of ChemistryVol. 21A, December 1982, pp. 1116-1119

Surface Tensions of Mixtures of Methanolwith Acetic Acid, Acetone, Chloroform,

Toluene & Carbon Tetrachloride

SURJIT SINGH*. BHAJAN S LARK &SURESH K AGGARWAL

Department of Chemistry. Guru Nanak Dev University. Amritsar143005

Rcceired 5 AIII(lIsl 19HI; reused and accepted 3 September 1982

Surface tensions of mixtures of methanol with acetic acid. acetone,chloroform, toluene and carbon tetrachloride have been measured at30KI5 K as a function of mixture composition. All the systems showpositive at: values. Melford equation has heen used to calculate theactivity coefficients in the surface phase.

Gibbs adsorption equation predicts the enrichment oflow surface tension component in the surface phaseleading to negative excess surface tension (at.:) forbinary mixtures. Such behaviour is generally met withmost of the mixtures. However, positive O'

E values havealso occasionally been reported for organic mixtures '.We have investigated the surface behaviour of mixturesof methanol with acetic acid, acetone, chloroform,toluene and carbon tetrachloride. These solvents wereselected in order to have variation in the shapes andspecific interactions. Interestingly enough, all themixtures show positive at.: values.

All the solvents were of AR(BDH) grade and werefurther purified by the methods described elsewhere".The purities of the samples were checked bydetermining their densities and refractive indices whichwere found to agree very well with those reported in theliterature.

Surface tension measurements were carried outusing differential capillary rise method. Capillariesu,,('d \lcre "f uniform bore. The ditTerenee in the levels(~hl of the liquid in the two capillaries was noted withthe help of a travelling microscope reading upto± 10 Jim. ~h values were corrected for the curvature ofthe meniscus by the formula.

... (1)

where ()'H is the corrected ()'h and (2 and t 1 are thethicknesses of the meniscus in the two capillaries. Asthe radii of the ca pillaries are small, further correctionswere found to be unnecessary. Surface tension. a, of theliquid having density II is given by Eq. 2.

a = «()'HP)/[~(~_~)Jg rl r,

tJ.HpC ' .. (3)

where C ~ ~(-~ - ~)g rl /'2

Capillary constant C was determined using purebenzene and carbon tetrachloride as calibratingsolvents: it was found to be 2454 ± 6 kg m - 1 N - '.Using this capillary constant, surface tensions of othersolvents used in the present studies were determined.These values compare very well with the literaturevalues.

Densities of binary mixtures required for theclaculations of surface tensions were calculated fromthe relation,

xtMt +X2M2P = ---- 0 o· E

XI VI +X2V2 + V

where M t and M2 are the molecular weights and V?and V~ are the molar volumes of the pure components.VE is the excess volume of the mixture with x 1 mole fra-ction of methanol. VE values for the binary mixtures ofmethanol with acetic acid;' chloroform", toluene" andcarbon tetrachloride" were taken from literature. Forthe methanol + acetone system, Vf

: is reported to beonly slightly negative 7 and is, therefore, assumed to bezero. For methanol +carbon tetrachloride", where VEis small (at x=0.5, VE= -41 x 1O-9m3mol-'), thesurface tension values differ on the average by ±0.014x 10- J N m - I if VE is assumed to be zero. Similarly,

the assumption that VE = 0 for methanol + acetonemixture is unlikely to affect the surface tensionsignificantly.

The uncertainty in the finally determined a valuesfor any mixture arises due to the uncertainties in themeasurements of (i) t\H (ii) density of mixture(iii) capillary constant and (iv) the temperaturevariation. The total uncertainty oa may be derivedfrom Eq. 4.

60' =

J (fdtJ.H)2

+ ( tJ.;dpr + (p~~ de r + ( G~}T Y... (4)

... (2) For dtJ.H=14Jlm, ;/p=O.lkgm-3, de=6 kgm-'N-t and dT=O.OI K.l5O' comes out to be±0.06x 1O-3Nm-l.or

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NOTES

Table I-Surface Tension, Excess Surface Tension and Activity Coefficient Data of the Two Components in the Surface

Phase as a Function of Composition

(J (JE r" rlI

---~-. ~-.-~ ------~-~---.----.-------

XI (I0-3Nm-l) (10-3Nm-l) (I0-"molm-2) (I0-6molm-2) x' ~ • .'i l'~. l "x, methanol + (I - x,) acetic acid

0.000 25.75 000 0.000 0.000 O.OO() 1000

0.144 26.57 147 0.226 0764 0.111 L54~ 10120.289 26.91 2A6 0.248 2.217 0.295 1.182 10800.395 26.59 2.61 0.399 3.604 OA44 1065 11470.480 26.18 2.58 0612 4.747 0.551 1027 11870.541 25.73 2.41 0.6X8 5.536 0.61X 1.0lX 1.201

0.583 25A8 2.35 0.703 6.061 0.659 1017 U030.658 24.91 2.11 0.668 6.98() 0.728 1.021 I I()~

0.746 24.17 177 0.579 8.102 0.803 1.025 1.178

0.889 22.94 1.18 0.429 10.217 0.928 10D 1.3021.000 21.26 0.00 0.000 11.628 1.000 1000

x, 1II£'lhallol+(I-x,) <I('('101l£'

0.000 21.78 0.00 0000 0.000 0.000 J.()()()

0.268 21.88 0.24 -0.034 1.674 0.263 1.042 0.999

0.367 2190 0.31 0.<X14 2.495 0.366 1.024 1007OAD 2188 0.34 0.041 3.51X OA78 1.009 1.0180.572 2183 0.35 0.076 4.6()9 O.SHI 1.0()2 10250.747 21.64 025 0.087 6.917 0.756 IO()() 10290.951 21.36 0.07 0.033 10.550 0.954 1000 ) .0321.000 2126 0.00 o.ooo 11.628 1.000 i.ooo

x, m('I/lllllo/+(I-,\,) chloroform

0.(0) 25.25 0.00 0.000 O.<X)O 0.000 1.0000.231 24.42 0.09 0.316 1.729 0.283 0.909 1.0070.289 24.18 O.OS 0.352 2.195 0.344 0.925 0.9990.330 23.99 0.06 0.362 2.527 0.385 0.939 0.990OAIO 23.65 0.04 0356 3.200 0.461 0.964 0.9720.504 23.35 0.11 0.337 4.080 0.549 0.984 0.9520.584 23.06 0.14 0.329 4.947 0.626 0.992 0.9410.704 22.61 0.17 0.323 6A99 0.741 0.995 0.9360.854 21.96 0.12 0.235 8.839 0.877 0.996 0.9270.899 21.73 0.07 0.174 9.625 0.888 0.998 0.9161000 21.26 0.00 0.000 11.628 1.000 1.000

X, melhallol + (I - x,) toluene

O.<X)() 26.75 0.00 0.000 0.000 0.000 1(0)0.193 26.02 O.D 0.231 1.202 0.239 0.950 0.9960.242 25.91 0.49 0.284 1.557 0.296 0.954 0.9940.324 25.57 0.60 0.368 2.204 0.389 0.969 0.9900.414 25.11 0.63 0.447 3.002 0.486 0.969 0.9840.627 23.99 0.68 0.543 5.431 0.968 0.985 0.9610.727 23.40 0.64 0.515 6.705 0.788 0.991 0.9440.777 23.07 0.59 OA75 7A64 0.830 0.994 0.9330.836 22.68 0.52 0.401 8.433 0.878 0:)96 09190.894 21.99 0.15 0.295 9A71 0.923 0.998 0.9021.000 21.26 0.00 0.000 11.628 1.<X1O 1.000

tContdi-~---~----~----------------.-- ---

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INDIAN J. CHEM., VOL. 21A, DECEMBER 1982

Table I-Surface Tension, Excess Surface Tension and Activity Coefficient Data of the Two Components in the SurfacePhase as a Function of Composition-Contd

(J (JE r~ r,

(10 -3Nm' ') xi 1,'. I 1'2

x, methanol + (1 - x,) carbon tetrachloride

0.000 ~4 ,~, 0.00 0.0000.222 ~j,~2 0.09 0.2340.267 24.0; 0.05 0.2670.444 2J41 0.10 0.3460.543 23.02 0.07 0.3550.605 22.82 0.10 0.3470.685 22.48 0.06 0.3200.761 22.24 0.10 0.2750.812 22.05 0.10 0.2350.915 21.62 0.05 0.1240.982 21.34 0.01 0.2871.000 21.26 0.00 0.000

0.000 0.000 1.0001.452 0.265 0.925 0.9921.785 0.314 0.933 0.9883.268 0.497 0.961 0.9694.251 0.592 0.973 0.9544.939 0.651 0.980 0.9445.928 0.724 0.987 0.9296.996 0.792 0.992 0.9137.800 0.837 0.995 0.9019.696 0.927 0.999 0.875

11.184 0.985 1.000 0.85711.628 1.000 1.000

Table 2--Parameters Used to Express the Surface Tensionas a Function of Mole Fraction and the Standard Deviation

of Experimental Values from the Function

Binary A, A2 A3 A4 Stmixture ----~-----.----- ..-- ------------ dev.

(I0--'Nm")

Methanol +acetic acid 10.130 4.227 2.6R5 -7.107 0.03Methanol+acetone 1.401 0.032 -0.582 -0.828 (>.01Methanol +chloroform 0.371 -1.058 1.271 2.450 0.01Methanol +toluene 2.822 -0.62R 0.08Methanol +carbontetrachloride 0.382 -0.119 0.02

._-----------

The experimental a values for the various systems asa function of mole fraction have been given in Table 1.The aE values have been calculated by Eq. 5,

... (5)

and fitted to Eq. 6,n

E x x' "A ( . x.)' - 1a =. I· 21.,. i 'X2 -"1 ... (6)

by least squares method. The Ai parameters and thestandard deviations for the various systems have beenincluded in Table 2. These seldom exceed ±O.03x 10- 3 Nm - 1. and therefore remain within the

expected uncertainties of ±O.06x IO-3Nm-l.It is apparent from the data given in Table 1 that all

the systems have positive aE values contrary to theexpected negative values. This shows preferredtendency of methanol molecules for the bulk phase inall these systems. The deviations are largest in the case

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of methanol-acetic acid system and show a maximum.This may be due to the formation of hydrogen bondedhetero complex. well evidenced in literature frommeasurements of other thermodynamic functions andspectral data:'. Acetone system also shows a maximumbut it is not pronounced. It may again be attributed tohydrogen bonded hetero complex. Other three systemsdo not show maxima; but, however, aE values arepositive against the expected opposite behaviour. aE

for toluene system is maximum and for equimolarmixture it is ~O.7xl0-3Nm-l. This may beattributed to the strong three dimensional associationof methanol molecules which pushes the toluenemolecules from the bulk to enrich the surface phasewhich is generally considered to be unimolecular thick.In the cases of carbon tetrachloride and chloroformsystems, aE values are not much larger than theexperimental uncertainties, but their consistentpositive sign confirms positive deviations. It may beconcluded that the three dimensional association ofmethanol molecules restrict its enrichment in thesurface even though its surface tension is lowest of allthe components studied.

The activity coefficient of a component in the surfacephase (Y," of a certain binary mixture may be calculatedfrom Melford equation (Eq. 7),

x (YI)e1a-a,)A,!RT +x (l'~)ela-a2)A2/RT = 11 }'~ 2\},~

... (7)

where Ai is the molar surface area of the COOiPO,.. '\1t iand may be calculated from the relation,

Ai=(nN)I!3(3/4 ViO)2!3

where V? is the molar volume.The assumption that ii and bulk phase activity

coefficients (}';)are equal, predicts a(cal.) from Eq. (3) to

be more than the experimental value for the mixtures ofmethanol with toluene, chloroform and carbontetrachloride which means that yf is less than Yi forthese systems. Opposite values are obtained for themixtures of methanol with acetone and acetic acid. Ifthe activity coefficients in the bulk phase are assumedto be unity then Gibbs adsorption equation can bewritten as,

r~=X2rl-Xlr2X1X2 do

=--x-RT dX1

... (8)

where I" I and F 2 are the numbers of moles ofcomponents 1 and 2 in the surface phase of unit areawhich, for a unimolecular thick surface layer, arerelated by the relation,

rIA1+r2A2=1

daldx, is obtained by differentiating Eq. (1), and thevalues of q and F I are given in Table I.

Under the assumption )'i= 1, Eq. (7) may berearranged to give,

... (9)

NOTES

where xi is the mole fraction of the ith component inthe surface phase which may be obtained from therelation,

rixi r, +r2

The results obtained (Table 1) are in agreement withthe qualitative conclusions arrived at above. Thepresent data reveal that in the case of methanol + aceticacid mixture, the activity coefficients in the surfacephase of both the components are significantly largerthan unity while for all the other systems they do notdiffer very much from the bulk activity coefficients.

References1 Myers R S & Clever H L,J Chem Engng Dota, 14 (1969) 91; 161.

2 Weissberger A & Praskaver E S. Organic solvents: physical

properties and methods of purification, Vol VII

(Interscience-John Wiley. New York), 1967.

3 Lark B S & Palta R C. J chem Thermodynamics. 12 (1980) 101.

4 Singh P P. Sharma B R & Sidhu K S. Can J Chem. 56 (1978) 2127.

5 Singh J. Excess ,'olumes ofsome binary mixtures, M Sc Thesis,Guru Nanak Dev University. Amritsar, 1980.

6 Paraskevopoulos G C & Missen R W. Trans Faraday Soc. 58(1962) 869 .

7 Campbell A N & Anand S C. Can J Chem, SO (1972) 1109.

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