Question

1. Element X has a mass of 300 g and a ½ life (t1/2)  of 10 years. How many grams will remain after 40 years? (Show your work) 

Answer 1

According to the decay rate equation:

$N_t=N_0×(1/2) ^{t/t_{1/2}}$

where N_t - final amount, N₀ - initial amount, t_1/2 - half life, t - elepsed time

From here:

$N_t = 300g × (1/2)^{40 years/10 years} = 18.75 g$

Answer: 18.75 g