Question

1. aluminum - 26 is a cosmogenic isotope, formed when cosmic rays strike a mineral when exposed. it has a half - life of 717,000 years. starting with a 25.0g sample how many grams of the sample disappears after 2,151,000 years?

Explanation:

Answer:

First, find the number of half - lives \(n=\frac{2151000}{717000}\approx3\).
Using the formula \(N = N_0(\frac{1}{2})^n\), where \(N_0 = 25.0\ g\) and \(n = 3\).
\(N=25.0\times(\frac{1}{2})^3=25.0\times\frac{1}{8}=3.125\ g\)
The amount of the sample that disappears is \(25.0 - 3.125 = 21.875\ g\)