How much of a 50.0 grams sample of Uranium-238 would remain after 26 minutes IF the half-live is 13.0 minutes?? This question has stummed me and I can't do it, ugh.

Question

How much of a 50.0 grams sample of Uranium-238 would remain after 26 minutes IF the half-live is 13.0 minutes?? This question has stummed me and I can't do it, ugh.

Answer 1

If the half life was 13 minutes, then 26 minutes is two half lives so you will have just 1/4 (1/2 x 1/2) o 12.5 grams.

Here is the way all of these are done.
k = 0.693/t_1/2 = 0.693/13 = 0.0533

Then ln(No/N) = kt
ln(50/N) = 0.0533(26)
ln(50/N) = 1.386
50/N = 4
N = 50/4 = 12.5