Practice!

Sample Problem

Given that the Ksp of CaF2 is 4.0 × 10-11, what is the concentration of fluoride ion if a 1.2 × 10-2 M CaCO3 solution is saturated with CaF2?

Solution

Let x = molar solubility of calcium fluoride

Because the Ksp of CaF2 is so small compared to the concentration of Ca2+ ions 1.2 × 10-2 + x  1.2 × 10-2