1) Ba-141 has a half life of 18.26 minutes and decays by first order kinetics. H
ID: 975779 • Letter: 1
Question
1) Ba-141 has a half life of 18.26 minutes and decays by first order kinetics. How many half lives will it take for a mole of Ba-141 to decay down to one atom?2) I-131 decays by first order kinetics. What will be the concentration of I-131 after 65 half lives if you start with a 2.57x10^2 grams of I-131. 1) Ba-141 has a half life of 18.26 minutes and decays by first order kinetics. How many half lives will it take for a mole of Ba-141 to decay down to one atom?
2) I-131 decays by first order kinetics. What will be the concentration of I-131 after 65 half lives if you start with a 2.57x10^2 grams of I-131.
2) I-131 decays by first order kinetics. What will be the concentration of I-131 after 65 half lives if you start with a 2.57x10^2 grams of I-131.
Explanation / Answer
1) rate constant k = 0.693/t1/2
t1/2 = 18.26 min
k = 0.693.18.26 = 0.038 min-1
1 mole of Ba = 141 g = 141 x 6.023 x 10^23 = 8.49 x 10^25 atoms
1 atom of Ba-141 = 1/8.49 x 10^25 = 1.18 x 10^-26
ln(1.18 x 10^-26) = ln(8.49 x 10^25) - 0.038 x t
t = 3142.24 = 172 half lives would be needed
2) (1/2)^n = amount remaining
n = half life = 65
0.5^65 = 2.71 x 10^-20 g remains after 65 half lives of I-131
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