The half-life of Sr-90 is 28 years.What mass of Sr-90 will remain unchanged if a 4.0 g sample decays for 84 years?

Question

Quizplus · Accepted Answer

Using the formula for half-life:

mass remaining = initial mass x (1/2)^(number of half-lives)

Since the half-life of Sr-90 is 28 years:

number of half-lives = 84 years / 28 years = 3

mass remaining = 4.0 g x (1/2)^3 = 0.5 g

Therefore, the mass of Sr-90 that will remain unchanged is 0.5 g, which corresponds to choice C.

The Half-Life of Sr-90 Is 28 Years