Indian Journal of Chemi ca l Technol ogy Vo l. 9, July 2 002. pp. 34 1-345 Articles Ultrasonic and vi scometric behaviour of hexadecane-butanol mixtures at different temperatures Rit a Mehra * & Rekh a Israni Depa rt me nt of Pure and App li ed Chemistry. Mahars hi Daya na nd Sa ras wa ti Uni vers it y, Ajmer 305 009 . In d ia Received 28 April 2001; revised recei ved 5 Ap ril 2002; accepted 10 May 2002 Ultrasonic speed, density and viscosity data were measured for binary mixtures of hexadecane and butanol over the entire range of composition and at different temperatures ranging between 298.15 and 318.15 K at 5 K From the experimental data, the values of adiabatic compressibility (K s ), excess adiabatic compressibility (K/), acoustic impendence (Z) , excess viscosity, excess free energy of activation of flow (G*E) were calculated. The results ar e interpreted in terms of degree of interaction between component molecules. The data at various temperatures also provide an opportunity to study the effect of temperature on the sign and magnitude of the deviation in compressibility. The co mp os iti on depe nd ence of ultraso ni c prope rti es of binary liquid mi xtures has proved to be a useful tool to inv es ti gate th e interac ti ons between th e co mponent s of binary liquid mi xtures. The ultraso ni c speed and th e rm odynami c data deri ve d from it has been widely used for thi s purposel- 6 . However, no att empt has been made to study th e ultr as onic and visco metri c behav iour of binary liquid mixtures of hexadecane and no rm al alcohols at different te mp eratures. In continuati on to th e rece nt studi es 7 - lo now ultraso ni c speed, vi sc osit y, densit y, adi abati c co mpressibility, acousti c impedence, excess vi scos it y, excess free energy of ac ti va ti on of viscous fl ow and excess adi aba ti c compressibility for mi xtur es of hexadecane a nd butanol at 298. 15 , 303. I 5, 30 8. 15 , 3 13. 15 and 3 18.1 5 K covering th e entire range of mole fr ac ti on of hexadecane are bein g reported. The significance of th ese parameters has been e mph as ized in und erstand in g th e nature of molec ul ar interac ti on be tween th e co mp one nt molec ul es. Experimental Procedure Hexadecane a nd butanol (S. D. Fin e Mumbai) with puri ty bett er than 99.5% we re used as such. The purit y of th e co mpo nents were ch ecked by co mp aring th e meas ur ed va lu es with th ose repo rt ed in literatur e. The ex perimental va lu es of th e dens ity and viscoc it y of hexadecane at 298. 15 K were 773 .3 kg m- 3 and 3.032x I0- 3 kg m- Is- I (l it erature va lu es : 772 .9 kg m- 3 and 3.03 lx IO- 3 kg m- Is - I ) and that of butanol at *For cor respondc nce: (Fax : 0 1 45-44 11 76) 298. 15 K we re 807 .8 kg m- 3 and 2. 5440x I0- 3 kg m- Is - I (l it erature va lu es : 809. 5 kg m- 3 and 2.5442x I0- 3 kg m- Is- I ) respec ti ve ly . The close ag ree ment between exp eriment al va lu es with those reported in literature asce rt ain th e re li abili ty of present res ults ll - 12 . Ultraso ni c speeds were measured by a si ngle crys tal ultraso ni c interferometer at 2 MH z frequ ency. These were accurate to 0.03%. The te mp erature was mainta in ed by circul ating water around liquid ce ll with a th ermostat contro ll ed at ±O .l 0 c. A bi capillary pykn ometer mounted in te mperature controlled wa ter bath was used for dens it y measurement s. The perc e nt age erro r in densit y measurement s is 0.024%. The vi scos iti es of pure liquid and th e ir binary mi xtures were measured by us in g an Ostwa ld 's viscometer with an accuracy of 0.09 %. Results and Di scussion Differe nt th e rm odyna mi c parameters such as adi abati c compressibility ( K s), acousti c impedance (2), have been co mputed us in g th e equ ati ons: 2 Ks= I/u P ... (I) . .. (2) The excess ad iaba ti c co mp ress ibility (K /), excess viscos it y (1 {), and excess free energ y of activation of visco us flow (C"E) have been calc ul at ed throu gh the relations 1 3. 1 5,