In dian Journal of Pure & Appli ed Physics Vo l. 4 1, February 2003, pp. 11 3- 120 Ultrasonic speeds and isentropic functions of mixtures of N-methyl-2-pyrrolidinone and branched alcohols at 298.15 K Amalendu Pal*", Harsh Kumar", B R Arbadb & A B Tekal eb "Department of Chemistry, Kurukshetra University, Kurukshetra 1 36 119 hDepartme nt of Chemistry, Dr B A Marathwada University, Aurangabad 43 1 004 *[e-mai l: search @vidya .kuk.ernet.in] Received 8 February 2002 ; re vi sed 9 Sep tember 2002; accepted I Novembe r 2002 Ult rasonic speeds have been measured for bi nary mixtures of N-methyl-2-pyrro li dinone with 2-propanol, 2-meth yl-1- propanol, 2-methyl-2-propa nol, and 3-mcthyl-1-butanol, as a func ti on of co mposition at 298 .1 5 K. The values have bee n comb ined with those of densities de ri ved from excess molar volumes to give es ti mates of the product Ks.m of the molar volumes and the isentropic compressibility Ks and the excess quantity K fm . The K fm values are negative over the entire range of composition for a ll mixtures. Th e deviation s 11D of the speeds of sound from their values in an ideal mixture were also ev aluated for a ll measured mole frac ti ons. Graphs of uD , and K fm against co mpositi on are presented as a basis for a quantitative discussion of the resu lt s. Va ri ous thermodynamic parameters have been der ived from the speed of so und data. Th eoretical values of speeds of sound 11 have also bee n determined using emp irica l relations. 1 Introduction Results of meas urements of some volumetric and transport properties of N-methyl-2- pyrrolidinone with branched alcohols at 298. 15 K have bee n prese nted in an ea rlier paper 1 • In a continuing effort to co ll ect further thermodynamic quantities of these mi xtures and also to extend the ava il a bl e database for N-methyl-2-pyrrolidinone + branched alcohol mi xtures, new experimental spee ds of sound u for the mixtures of N-methyl- 2- pyrrolidinone with 2-propanol, 2-methyl-1- propanol, 2-methy l- 2-propanol, or 3-methyl-1- butanol ove r the whole mole frac ti on range at the tempera ture 298. 15 K and atmosphe ri c pressure are reported in this pape r. Th e isentropic co mpressibility Ks for a ll mixtures were estimated by co mbining the densities de ri ved from the excess molar volumes 1 and the measured ultraso ni c spee d s. Th e molar volumes we re multiplied by the values of isentropic compressibility, to obta in es timates of Ks. rn · Th e authors have also ca lculated devia ti ons uD of the spee ds of so un d u from those in th e id ea l mi xtures uid, to 0 cre ther with the excess molar quantiti es K 5 E . ,m To inves ti gate the nature of interac ti ons, va ri ous thermodynamic parametersv h ave bee n ca lc ul ated, which are sensitive to interac ti ons between solute and solvent. Th eoreti ca l va lu es of spee ds of so un d have bee n estimated using different empiri ca l equations. 2 Experimental Details 2.1Materials Mate ri als we re of the same origin and purit y, as used in the ea rlier study' . All liquids we re kept in ti ghtly sea led bottles to minimize the absorption of atmosphe ri c moisture and C0 2 , and dried over 0.4 nm mol ec ular sieves to redu ce wa ter co ntent Befo re meas urements, a ll liquids were partia ll y de-gassed at low pressure. By comparing the densities at (298. 15 ± 0 .0 I) K and a tmos phe ri c press ure with their corresponding litera ture values 4 • 11 (Ta bl e I) the purity of the liquids was chec ked. Also given in Ta bl e l are the meas ured or litera ture va lu es of th ose quantities w hi ch were re quir ed in the estima ti on of Ks. 111 , K J 111 , and uD . Th e co mposition of each mixture was obtained with an un ce rt a in ty of I x I 0-4 from the measured apparent masses of one of the co mpone nt s. All the mass meas urements were performed on an el ec trica l balance ( Dh ona 2000 , In dia), accurate to ± 0.1 mg. Co rr ec ti ons were made