An interpretation for the distance parameter of the Fuoss-Onsager conductance equation in the case of ionic association

✍ Scribed by J.-C. Justice

• Publisher: Elsevier Science
• Year: 1971
• Tongue: English
• Weight: 961 KB
• Volume: 16
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(71)85038-7

✦ Synopsis

A discussion is given of the various anomalies apparent in the literature since the publication of the Fuoss-Onsager conductance equation in 1957. A careful re-analysis of available conductance data leads to a reconsideration of the physical meaning of the distance parameter in agreement with Bjemun's concept for the distinction between short and long-range electrostatic, interactions. The conclusion is that the generalization of the original Fuoss-Onsager conductance equation to the case of association must be identical with that proposed originally by Bjerrum in 1926, for the Debye-Hiickel treatment of activity coefficients. R&um&--Les di%rentes anomalies soulign&s dans la litt&ature depuis la parution de I%quation de ConductibilitC de Fuoss-Onsager en 1957 sont discutees et interpr&%s. Une nouvelle expIoitation plus rigoureuse des donnCes conductim&riques disponibles conduit A une interpr&ation de la signification physique du param&re de distance en accord aver le concept de Bjerrum concernant la distinction entre les interactions &ctrostatiques & courte et Iongue distance. La conclusion de ce m&moire est que la g&&+lisation au cas de l'association de 1'6quation de conductibilit6 de Fuoss-Onsager doit Qtre identique B celle que Bjerrum avait proposb en 1926 dans le cas de la thbrie du coefficient d'activite de Debye et Hiickel. Zusammenfassmg-Die verschiedenen Anomalien, welche in der Literatur seit der Veriiffentlichung der Leitf5higkeitsgleichung von Fuoss-Onsager im Jahre 1957 gefunden wurden, werden diskutiert. Die sorgf&ltige Untersuchung der vorhandenen Leitftigkeitsdaten fiihrt zu einer neuen Betrachtung der physikalischen Bedeutung des Distanzparameters in ~hereinstimmung mit dem Konzept von Bjerrum fT.ir die Unterscheidung der elektrostatischen Wechselwirkungen iiber kurze beziehungsweise lange Strecken. Es wird geschlossen, dass die Verallgemeinerung der urspriinglichen Fuoss-Onsager-Gleichung fiir den Fall von Assoziation identisch sein muss mit der von Bjerrum 1926 im Falle der Theorie fiir den Aktivitstskoeffizien ten nach Debye-Hiickel vorgeschlagenen Gleichung. THE THEORY of conductance of symmetrical electrolytes in dilute solutions consists of the following set of equations, A = yu.0 -Sc1'2y1'2 + Ecy log cy + J(R)cy + J3&?)c3'2p'~], (1) 1-Y ___ = K,, Y2C.* '2 (2) lny,' = -A6 1 +B.R.G' (3) Equation (1) is a series expansion of various conductance equations treated by Pitts,l Fuoss and Onsager, Mirtskhulava, 3 Kelbg4 and recently Fuoss and Hsia,s to which is added the concept of ion association to non-conducting pairs, leading to the introduction of the fraction y of free ions. A recent publication* deals with the analytical differences concerning the coefficient E and the functions J(R) and J,,,(R) of the distance parameter R in the various equations mentioned.

Equation (2) takes into account the equilibrium between free and associated ions. In that equation, the activity coefficient of free ions is y+ ', that of the associated pairs is assumed to be equal to unity.