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?
140 / 200 = (1/2)^(60 / h)
log(.7) = (60 / h) log(.5) ... h = 60 * log(.5) / log(.7)
(b) log(.20) = (t / h) log(.5) ... t = h * log(.20) / log(.5)