The half-life of Au-198 is 2.7 days.What mass of Au-198 will remain unchanged if a 12.0 g sample decays for 13.5 days?

Question

Quizplus · Accepted Answer

Using the formula for half-life:
Nf = Ni (1/2)^(t/T)

where Nf is the final amount, Ni is the initial amount, t is the time elapsed and T is the half-life.

We can find Ni:
Ni = Nf/(1/2)^(t/T)
Ni = 12.0 g/(1/2)^(13.5/2.7)
Ni = 12.0 g/16
Ni = 0.75 g

Therefore, the mass of Au-198 that remains unchanged is 0.75 g. Choice D is the correct answer.

The Half-Life of Au-198 Is 2