Calcium fluoride, CaF2, is a very slightly soluble salt. In Example 17.4, we calculated its solubility from the solubility constant, assuming that the solubility equilibrium represented by Ksp was the only important one. However, a solution of the salt does contain the species HF. Where does this come from? Would you expect this to increase or decrease the solubility as we calculated it in the example? Using the fluoride-ion concentration that we calculated in the example, obtain the concentration of HF in the solution. From this, decide how important the formation of fluoride ion is in determining the solubility of calcium fluoride. Without doing any calculations, decide how important you think a similar effect would be in determining the solubility of calcium carbonate. Explain.