Apparent Molal Volumes of n-Alkylammonium Chlorides and Sodium n-Alkanecarboxylates in Dilute Aqueous Solutions

• Published in: Bulletin of the Chemical Society of Japan Vol. 48; no. 12; pp. 3491 - 3495
• Main Authors: Sakurai, Masao, Komatsu, Tsuyoshi, Nakagawa, Tsurutaro
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 01.12.1975; Chemical Society of Japan
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.48.3491

The densities of dilute aqueous solutions of two homologous organic salts, RNH3Cl and RCOONa, where R varies from H to n-octyl, have been measured at 5, 25, and 45 °C using a buoyancy technique. The apparent molal volumes, φv, of the salts and the limiting partial molal volumes, \barV°, of the individual ions have been evaluated. The contributions of a methylene group to the partial molal volume, \barV°(CH2), as estimated from the \barV° data for longer-chain salts, are nearly the same for both series: approximately 15.3, 15.9, and 16.5 ml/mol at 5, 25, and 45 °C respectively. Compared to these values, on the other hand, the \barV°(CH2) estimated for shorterchain RNH3Cl is larger and that for shorter-chain RCOONa is smaller. The second derivative of the \barV° with respect to the temperature, ∂2\barV°⁄∂T2, which is often regarded as a useful measure of structural effects, is almost independent of the chain length for longer-chain homologues. The concentration dependence of φv does not always vary in a regular manner with the chain length. The present results suggest that the volumetric behavior of aqueous organic electrolyte solutions is more complicated than has previously been believed.