A water treatment plant adds fluoride ion to the water to the extent of 1.5mg F-/L H2O. a)What is the molarity of fluoride ion in this water? b)If the fluoride ion in the water is supplied by calcium fluoride, what mass of calcium fluoride is present in 1.00 x 10^6 L of this water?

Answer 1

1.5 mg/L = 0.0015 g/L
mols F = 0.0015 g/atomic mass F = ? and that is mols/L so = ? M = approx 8E-5 mols/L but that is an estimate.

In 1E6 L there will be approx 8E-5 mols/L x 1E6 L = approx ? mols F.

You will need 1/2 that mols CaF2 since CaF2 contains 2 mols F for every mols CaF2. Then g CaF2 = mols CaF2 x molar mass CaF2.