Dilution of a weak acid-base system at equilibrium would be expected to cause a change in pH. If the
major species is
the acid, the pH should increase (become closer to 7) due to less H3O+.
the base, the pH should decrease (closer to 7) due to less OH–.
The extent of change is less than would be expected on the basis of the dilution factor.
Thus, dilution of a solution of a weak base (or of a solution of a weak acid) by a factor of 10 causes a change in pH of less than 1. The reason for this is described on the next page.