For 2.0 mole of the radioactive isotope molybdenum-99, half-life = 67 hours, how many disintegrations?

Question

have occurred after 17 minutes?

Answer 1

Basically, 2 moles = 1.2x10^24 atoms. We want to know how many have gone after 17 minutes.

Half-life is really not a good way to go after this. I favor using the decay constant, which is more flexible. This constant, k is obtained from the half-life. 67(60) k = 0.693
(we want an answer based on minutes)
k = 0.693/4020=1.72x10-4 min appx. now C= Co exp(-kt) or exp is 2.7182
So C(17 min)= 1.2x10^24exp(-17x1.72x10-4)
C(17 min)=1.2x10-24exp(-.0029) and solve. The difference between 1.2x10-24 and C(17 min) is what you need.