Planck-Henderson expression

This is the usual Planck-Henderson expression for the diffusion potential. In the present situation it is containing the contribution of the protons and only. Eliminating AVfrom Eqs. (1) and (4) we have... 

Henderson (/ c) has likewise dealt with the general case, in which the two solutions differ in concentration, and have not necessarily any ion in common, and the 10ns not being necessarily of the same valency This method is more readily followed than that of Planck, but there is not space to give it here The final expression reached is—... 

If one considers a sample solution and bridge electrolyte of any desired composition, one must make assumptions about the concentration gradient within the liquid junction in order to arrive at simplified expressions. While it is possible to numerically simulate these profiles on the basis of the Nemst-Planck equation,for practical purposes it is perfectly acceptable to use the Henderson equation as approximation. It assumes linear concentration gradients across the Jimction and is written as ... 

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