CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
Solid calcium fluoride, CaF2, is sparingly soluble in water at 25 °C. At this temperature the solubility product constant is Ksp=3.9×10−11 and the acid-dissociation constant of hydrofluoric acid is Ka=6.6×10−4.
(a) Calculate the molar solubility of CaF2 in pure water at 25 °C.
(b) Calculate the molar solubility of CaF2 in a solution that is buffered to pH 3.00 at the same temperature.
(c) Determine the factor by which the solubility changes when the pH is lowered from the value obtained in part (a) to pH 3.00. Express the factor to two significant figures.
(d) Explain, in terms of the relevant equilibria, why the solubility changes in the direction indicated in part (c).