Ion Transport in Solution

Semiconductor Electrochemistry, Zweite Auflage. Rudiger Memming. 

When different salts are dissolved in the electrolyte, the conductivity can be expressed in more general terms 

The mobiUty of an ion is related to the velocity v and the electric field in which an ion is moving. The corresponding electric force, z e , accelerates the ion until the frictional drag exactly counterbalances the electric force. The frictional drag can be approximated from Stokes law as 6n//r v, in which tj is the viscosity of the solution, r is the radius of the ion, and v is the velocity. Using these equations and the definition of mobihty, namely, = vj , one then obtains 

This equation also implies the definition of individual equivalent conductivities, so that we have, according to Eq. (3.5), 

In addition, it is common in electrochemistry to use transference numbers defined as 

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The Mechanism of Ion Transport in Solutions, Solids, Melts and Polymers... 

In volume 1 (Chapters 4 and 5) a fairly detailed treatment of the movement and transport of ions was presented qualitative pictures and quantitative accounts were given of the diffusion and electrical migration of ions in the bulk of the electrolyte. In the treatment of electrodic processes, no mention was made at first of a connection between the transport in solution and processes at electrodes. It was then realized that this neglect of ion transport in solution (ionics) was tantamount to assuming that at no stage in the course of a charge-transfer reaction did the interfacial concentrations of electron acceptors and donors depart from their bulk values. 

This text discusses four aspects of ionic electrochemistry ion-solvent interactions, ion-ion interactions, ion transport in solution, and ionic liquids. 

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