You must take HF into consideration during the calculation.
The whole point of these problems is to show you that BaF2 has a certain solubility in neutral solution. As the solution becomes more and more acid the formation of HF becomes more (because HF is a weak acid); that shifts the solubility equilibrium to the right and makes BaF2 more soluble in acid solutions.
Consider the two equilibria:
BaF2=Ba2+ + 2F- Ksp=1.7x10^(-6)
F- + H20=HF + OH- Kb=2.9x10^(-11)
Determine the solubility of BaF2 at pH=5?
What I'm mostly confused about is how to determine if F- is dominant or if you have to take HF into account while doing your calculations.
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