it has a half-life, so we expect a function like
y = a(1/2)^(x/h)
where h is the half-life. We have the point (1,140) on the curve, so
200(1/2)^(1/h) = 140
1/2^(1/h) = 0.7
1/h = log0.7/log0.5 = 0.515
h = 1.943 minutes
and that means y = 200(1/2)^(x/1.943)
so now find x when y=0.2*200 = 40
1/2^(x/1.943) = 0.2
x/1.943 = log0.2/log0.5 = 2.322 (half-lives)
x = 4.512 minutes
oops. I just noticed that it wants the equations in terms of seconds, so just make that adjustment.
OBronium-12 is a radioactive material that spontaneously decays when it comes in contact with oxygen. One minute after a 200-mg sample of OBronium-12 is placed into an oxygen chamber, only 140 mg remains. Round your answers to 1 decimal place.
a) Determine the half-life of OBronium-12 in seconds.
b) After how long would there be 20% of OBronium-12 left in seconds?
2 answers
np, thank you so much