journalof MOLECULAR LIQUIDS E LS EVI E R Journal of MolecularLiquids 89 (2000) 169-174 www.elsevier.nl/Iocate/molliq Apparent Molar Volumes of Some Symmetrical Tetraalkylammonium Bromides in Methanol + Acetonitrile Mixtures at 298.15 K Nirmal Saha, and Bijan Das* Department of Chemistry, North Bengal University, Darjeeling 734 430, India Received 18 May 2000; accepted 27 September 2000 Abstract The apparent molar volumes of six symmetrical tetraalkylammonium bromides, R4NBr (R = ethyl through heptyl) have been determined in methanol + acetonitrile binary mixtures (containing 0.20, 0.40, 0.60 and 0.80 mole fractions of acetonitrile, x) over the concentration range (I.005 - 0.065 mo].kg': at 298.15 K from precise density measurements. Use has been made of the nonthermodynamic, so-called extrapolation method to split the limiting apparent molar volumes into ionic contributions. The results have been interpreted in terms of ion-ion and ion-sol\ ent interactions. © 2000 ElsevierScience B.V. All rights reserved. Introduction Ihc volumetric behaviour of solutes has been proved to be very useful in elucidating various interactions occurring in solutions) Studies on the apparent molar volumes of electrolytes haxc been widely used to examine the ion-ion, ion-solvent, and solvent-solvent interactions.-' Thc apparent molar volumes of tetraalkylammonium salts have been investigated rather cxtcnsively in aqueous, organic, and aquo-organic solvent systems.244 However, such measurements involvintg mixtures of organic solvents are relatively scarce. The present paper reports thc apparent molar volumes of six symmetrical tetraalkylammonium bromides, R4NBr (R = ethyl through heptyl) in methanol + acetonitrile mixtures containing 0.20, 0.40, 0.60 and 0.80 mole tiactions of acetonitrile ( x ) at 298.15 K. Experimental Nlcthanol (E. Merck, India, uvasol grade, 99.5% pure) was dried over molecular sieves and distilled fractionally. Tke middle fraction was collected and redistilled. The purified solvent had a density of 0.78654 g.cm 3 and a viscosity of 0.545 mPa.s at 298.15 K. These values agree x~cll ~ith the literature values, is Acetonitrile (E. Merck, India, 99% pure) was distilled with P2Os and then redistilled over Calt,. rile purified solvznt had a density of 0.77686 g.cm3 and a viscosity of 0.345 mPa.s at 2,)8i 5 K, these values are also found to be in good agreement with literature values] 6'17 lch-aalkylamn~onium bromides were of purum or puriss grade (Fluka) and were purified as described in the literature) 8":9 The salts were purified by recrystallisation and the higher homt~logues were recry:;tallised twice to ensure highest purity. The recrystallised salts were dried under vacuum at 373.15-383.15 K for 24 h. Owing to the hygroscopic nature of the salts, 0167-7322/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII S0167-7322(00) 00160-4