Why do solutions of barium chloride, and barium fluoride give rise to solutions with different pH values?
Answer:
Because
fluoride ion undergoes hydrolysis in aqueous solution.
Explanation:
Consider the solubility equilibrium for \(B a F_{2} \text { : }\)
Fluoride is moderately basic………….
\(\mathrm{F}^{-}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{HF}(a q)+\mathrm{HO}^{-}\)Addition of \(\mathrm{H}_{3} \mathrm{O}^{+}\) will drive these equilibria to the right as written, and MORE barium salt will go into solution.
On the other hand, chloride ion, A WEAK BASE, does not speciate in solution, and is inert to added acid.
Note that had we \(K_{\mathrm{sp}}\) data for \(B a F_{2}(s)\), and \(K_{a}\) data for \(H F\) we could solve the solubility equilibrium precisely, and develop an expression for solubility that depends on \(p H\).