It is recommended that drinking water contain 1.6 ppm fluoride (F-) for prevention of tooth decay. Consider

Question:

It is recommended that drinking water contain 1.6 ppm fluoride (F-) for prevention of tooth decay. Consider a reservoir with a diameter of 4.50 × 102 m and a depth of 10.0 m. (The volume is πr2h, where r is the radius and h is the height.) How many grams of F- should be added to give 1.6 ppm? Fluoride is provided by hydrogen hexafluorosilicate, H2SiF6. How many grams of H2SiF6 contain this much F-?