# Question 568a2

Jun 19, 2017

The amount that remains unchanged is 2.5 g.

#### Explanation:

The half-life of tritium is 12.32 years.

The formula for calculating the amount remaining after a number of half-lives, $n$, is

$\textcolor{b l u e}{\overline{\underline{| \textcolor{w h i t e}{\frac{a}{a}} A = {A}_{0} / {2}^{n} \textcolor{w h i t e}{\frac{a}{a}} |}}} \text{ }$

where ${A}_{0}$ is the initial amount and $A$ is the amount remaining.

n = 36.93 cancel("y") × "1 half-life"/(12.32 cancel("y")) = "2.998 half-lives"#

$A = {A}_{0} / {2}^{n} = \text{20 g"/2^2.998 = "2.5 g}$