Problem 16-50

A pH-sensitive salt contains an anion or cation considered to be a weak acid or a weak base

for example:
AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq) neither of these ions are the conjugate base (or acid) of a weak acid (or base).
Therefore, AgCl is not affected by the pH

However, AgF(s) ⇌ Ag⁺(aq) + F⁻(aq)

F⁻ is the conjugate base of the weak acid HF.
In this case, F⁻ will be "consumed" if the solution is acidic: F⁻ + H⁺ → HF
Since there will be less F⁻(aq) present in the solution, the AgF salt will be more soluble, therefore affected by the pH.