Whether an acid will behave as a strong or weak acid thus depends both on the acid and the solvent. Because the fluoride ion, F^-, is small, thus permitting the proton to come close to it and feel a strong electrostatic attraction, it is a moderately strong B-L base.

Even though water molecules are present in great excess, the attraction of F^- for protons is great enough that HF is only partially dissociated in aqueous solution. In contrast, the Cl^- ion is large, with a diffuse electron density, and does not permit the proton to approach as closely. It attracts protons more weakly, and is a weak B-L base.

So many molecules of H₂O surround each Cl^- ion that they overwhelm Cl^- and compete successfully for the available H⁺ ions, thereby pushing the dissociation equilibrium effectively to completion. Hence HCl is classed as a strong acid in water.

In methanol, Cl^- ions in similar concentration find no difficulty in competing successfully with an excess of CH₃OH molecules for the available H⁺, because of the very small attraction of CH₃OH molecules for H⁺. Even in methanol, however, perchloric acid is a strong acid because the perchlorate ion, ClO₄^-, has less attraction for protons than methanol molecules do. HClO₄ is the strongest of all the common acids because ClO₄^- is the weakest of all the B-L bases.

Sulfuric acid can lose two protons. The first dissociation is that of a strong acid, and is complete in aqueous solution:

The bisulfate ion, HSO₄^-, is more reluctant to lose another positive ion, since it already has one negative charge. The sulfate ion is a strong B-L base, and competes successfully with water molecules for the proton. Therefore HSO_4^- is a weak acid with a measurable dissociation constant:

Phosphoric acid has three dissociating protons, of varying degrees of weakness: