If 125. mg of fluorine-18 is shipped at 10:00 A.M., how many milligrams of the radioisotope are still active after 330 min ?

Question

 Chemistry 106, conversion is involved

Answer 1

You need to know the half-life for F-18. Looking it up, you find it to be 109.771 minutes.

Fraction remaining = 0.5^n where n = number of half lives elapsed, = 330min/109.771 = 3.006 half lives

Fraction remaining = 0.5^3.006 = 0.1244

mass remaining = 125. mg x 0.1245 = 15.6 mg (to 3 sig. figs.)