Using mass percentages:-

The American Dental Association recommends that you should consume 3.0 mg of fluoride a day. If you get your fluoride in the form of sodium fluoride, what mass of sodium fluoride should you ingest?

3 mg F^- x (molar mass NaF/atomic mass F^-) = ? mg NaF.

To calculate the mass of sodium fluoride you should ingest to obtain 3.0 mg of fluoride per day, we need to consider the mass percentage of fluoride in sodium fluoride.

The molecular formula of sodium fluoride is NaF, which consists of one atom of sodium (Na) and one atom of fluoride (F).

To determine the mass of fluoride in sodium fluoride, we need to find the molar mass of sodium fluoride and the mass percentage of fluoride in it.

The molar mass of sodium (Na) is 22.99 g/mol, and the molar mass of fluoride (F) is 18.99 g/mol. Adding these two values together gives us the molar mass of sodium fluoride:

Molar mass of NaF = 22.99 g/mol + 18.99 g/mol = 41.98 g/mol

Now, to calculate the mass percentage of fluoride in sodium fluoride, we divide the molar mass of fluoride by the molar mass of sodium fluoride and multiply by 100:

Mass percentage of fluoride = (18.99 g/mol / 41.98 g/mol) x 100 = 45.23%

This means that in 100 grams of sodium fluoride, approximately 45.23 grams is fluoride.

Now, to find the mass of sodium fluoride you should ingest to obtain 3.0 mg of fluoride, we set up the following proportion:

(3.0 mg / 45.23 g) = (x / 100 g)

Cross-multiplying and solving for x (the mass of sodium fluoride) gives us:

x = (3.0 mg * 100 g) / 45.23 g
x ≈ 6.63 mg

Therefore, you should ingest approximately 6.63 mg of sodium fluoride to obtain 3.0 mg of fluoride per day, according to the recommendations of the American Dental Association.