More to the point, though, is the fact that the pH system, rests on the fundamental assumption that the solution is dilute enough that interaction between solute ions is negligible, which allows the only relevant equilbrium to be that of the (de)protonation of the solute ions. Mathematically, this means that systems can be model in terms of a exponential equation, the logarithm of which is the linear pH scale.

As solutions become more concentrated, solute-solute interactions can no longer be ignored, and the deviations from linearity in the pH scale become more easily measurable. Hence, diluting a concentrated base soluton can result in a decreased pH.