Fluoridation of drinking water is employed in many places to aid in the prevention of dental caries. Typically the F- ion concentration is adjusted to about 1 ppb. Some water supplies are also "hard"; that is, they contain certain cations such as Ca2+ that interfere with the action of soap. Consider a case where the concentration of Ca2+ is 8 ppb.
Could a precipitate of CaF2 form under these conditions? (Make any necessary approximations.)