Question

The half life of 14O is 71 seconds. If you start with 147.2 milligram sample of 14O how much of the sample is left after 284 seconds

Answer 1

half - life = 71 sec

rate constant k = 0.693 / t1/2

                         = 0.693 / 71

                         = 9.76 x 10^-3 s-1

initial mass = 147.2 mg

time = 284 sec

k = 1/t ln (Ao / At)

9.76 x 10^-3 = 1 / 284 ln (147.2 / At)

At = 9.205

mass of sample left over = 9.205 mg