Transport Properties of Ions

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There are three modes of transport of ions in solution: diffusion, migration and convection. The factors that encourage ions to move in these modes are, in the case of diffusion, a concentration gradient; in the case of migration, a potential gradient; in the case of convection, either a temperature gradient or mechanical stirring or flow.

The electrical potential of species i is defined as

Spontaneous movement of i will take place from regions of higher to lower electrochemical potential. The rate of such movement is proportional to the gradient where x is the distance of i from a reference plane so that