A 250 mL aqueous solution contains CaCl2 at a concentration of 0.020 M. Solid NaF is gradually added with continuous stirring until CaF2(s) first begins to form.
(a) Write the equilibrium expression associated with the dissolution of CaF2(s) in water.
(b) Using Ksp=3.9×10−11 for CaF2, determine the minimum molar concentration of F− that must be present in the solution at the moment precipitation starts.
(c) Calculate the minimum number of grams of NaF(s) that must dissolve in the 250 mL of solution to achieve the concentration found in part (b). Assume the added solid does not change the volume appreciably.