The decay: 17578Pt→42He+17176Os has a half life of 2.53 seconds.If you originally begin with 158.7 grams of 175Pt, how many grams of 171Os would you have after 7.59 seconds?

Answer 1

One of the easier ways to solve these first order decay problems is by using the simple expression...

F = 0.5ⁿ

F = fraction remaining

n = number of half lives that have elapsed

In this problem we can find the number of half lives that have elapsed (n) as follows:

7.59 sec x 1 half life/2.53 sec = 3 half lives = n

F = 0.5³

F= fraction remaining = 0.125

grams remaining = 0.125 x 158.7 g = 19.84 grams