Express the concentration of a 0.0250 m aqueous solution of fluoride, f–, in mass percentage and in parts per million. assume the density of the solution is 1.00 g/ml.

Assume that you have 1 L of solution. 

moles of F- = conc. x volume = 0.025 x 1= 0.025 moles F- 
0.025 moles  x (19.0 g/mole) = 0.475 g in 1 L of solution = 475 mg

mass of solution = density x vol = 1 g/ml x  1000ml = 1000 g solution 

mass % F- = (mass of F- / mass of solution) x 100 = (0.475 / 1000) x 100 = 0.0475% 

One ppm is equivalent to 1 milligram of something per liter of water (mg/l) .

parts per million F - = mass of F- in milligram / volume in L = 475 / 1 = 475 ppm F-

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