fluorine-18 is used in medical imaging. If a lab has a sample containing 15 g of fluorine-18, how much fluorine-18 will remain in the sample after 8.0 h?

Answer 1

To answer this, we need to know the half life of Fluorine-18. Looking it up, I find a value of 109.7 minutes.

The easiest formula to use is the following (there are others, of course): FR = 0.5ⁿ

FR = fraction remaining

n = number of half lives that have elapsed

Using a half life of 109.7 minutes, we can find out how many half lives have elapsed in 8.0 hrs as follows:

8.0 hours x 60 min/hour x 1 half life/109.7 min = 4.38 half lives have elapsed

FR = 0.5^4.38

FR = 0.0480

Since we started with 15 g, the mass remaining will be...

15 g x 0.0480 = 0.72 g remains