Question

The half-life of iodine-131 is 8.07 days. If 0.25 g are left after 40.35 days, how many gramswere in the original sample?

Answer 1

See below

Step-by-step explanation:

40.35 days / (8.07 day per half life) = 5 half lives

.25 = x ( 1/2)^5

.25 / ( 1/2)^5 = x = 8 gm originally

Answer 2

Given data

*The half-life of iodine-131 is t = 8.07 days

*The amount of quantity left is N = 0.25 g

*The number of days is T = 40.35 days

The expression for the radioactivity decay is given as

`N=N_0((1)/(2))^{(T)/(t)}`

Substitute the values in the above expression as

`\begin{gathered} \text{0}.25=N_0((1)/(2))^{(40.35)/(8.07)} \\ N_0=8\text{ g} \end{gathered}`