1. Calculate the percent fluoride by weight in H2SiF6. 2. Minnesota Statutes req
ID: 544225 • Letter: 1
Question
1. Calculate the percent fluoride by weight in H2SiF6.
2. Minnesota Statutes require all municipal water supplies to maintain a fluoride concentration of 0.9 ppm to 1.5 ppm (measured as mass of F per liter), with an optimum level of 1.2 ppm (measured as mass of F per liter). The city of Mankato, MN uses groundwater wells for water supply. The flow of one of the wells is 1,000 gallons per minute (gpm) and runs for 24 hours. The city aims to achieve optimum concentrations of fluoride. The city uses hydrofluorosilicic acid (H2SiF6) with 25 % purity. How many gallons of acid per day must the city add for each well to keep the concentration to 1.2 ppm?
3. According to the fluoridation reaction given above, how much fluoroapatite, Ca5(PO4)3F, is produced when the concentration of hydrofluorosilicic acid,H2SiF6, is supplied at 1.2 ppm?
Tooth decay: Ca5(PO4)3OH(s) + 4H3O+ 5Ca2+ + 3HPO4 2- + 5H2O
Fluoridation: 6Ca5(PO4)3OH(s) + H2SiF6 6Ca5(PO4)3F(s) + SiO2 + 4H2O
Explanation / Answer
1. Calculate the percent fluoride by weight in H2SiF6.
% F in H2SiF6 = 6*MW F / Total mass H2SiF6 * 100%
% F in H2SiF6 =6*18.99/144.09 * 100
% F in H2SiF6 = 79.07 % is F
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