Summary 4

If base is added:

HF (aq) +OH− (aq) ⇌ F− (aq) +H2O (l)

In this reaction, the conjugate acid, HF, will neutralize added amounts of base, OH-, and the equilibrium will again shift to the right, slightly increasing the concentration of F- in the solution and decreasing the amount of HF slightly. Again, since most of the OH- is neutralized, little pH change will occur.

These two reactions can continue to alternate back and forth with little pH change.