If 100.0 g of a radioactive isotope that has a half life of 25 years, identify the amount of that isotope that will remain after 100 years?

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Answer 1 · 2014-05-17T13:06:34

The amount remaining will be 6.2 g.

The number of half-lives is #n = t/t_½#

For each half-life, you divide the total amount of the isotope by 2, so

Amount remaining = #"original amount"/2^n# or

#A = A_0/2^n#

#n = t/t_½ = (100" yr")/(25" yr")# = 4.0 half-lives

#A = A_0/2^n = (100.0" g")/2^4.0 = (100.0" g")/16# = 6.2 g