Relative Acidity

[205389184]

Can there ever be a case in which the resulting anion is not stable?

[Chem_Mod]

The resulting anion is not stable when a weak acid like HF dissociates in water. For example, F minus is not a stable anion so it reacts as a base in water and pulls of a hydrogen from water, generating OH-. Keep in mind that stability is relative.
F- + H20 --> HF + OH-

[Chantel_2I]

When the anion is unstable, the salt changes the pH of the solution because the anion may pull a H proton off of a water molecule, turning it into -OH, making the solution more basic.

[Jainam Shah 4I]

The anion of a weak acid tends to be unstable, because a weak acid's reaction is reversible. Something like HCl would completely disassociate so the chlorine would be stable and it would make no effort to snag a H+ because there is no HCL left in the water. The conjugate base or Cl- is stable. In something like HF, a weak acid, the acid's disassociation is reversible. So even though the acid produces F-, the F_ haas a tendency to attract a proton and return to HF because in a weak acid some acid remains in water not disassociated.