Question

The radioisotope radon-222 has a half-life of 3.8 days. How much of a 98.4 g sample of radon -222 would be left after approximately 19 days?

Answer 1

98.4 * (1/2)^(19/3.8) = 3.075 g

Answer 2

Cf = Ci(e^-kt)
Ci = 98.4 gms
Cf = ?
k = (0.693/3.8)days^-1 = 0.8663 da^-1
t = 19 days
Cf = Ci e^-kt
Cf = 94.4gms e^-[(0.8663da^-1)(19da)]
Cf = (94.4)(7.11 x 10^-8)gms
Cf = 6.7 x 10^-6 gm remains

Answer 3

two errors, DrRebel:
(0.693/3.8) ≠ 0.8663
it was 98.4, not 94.4