Asked by jess

Iodine-131 has a half-life of 8 days. How many grams of a 12 g sample will remain at the end of 40 days?

how do i solve this? i thought it was
12^40=1.5 but that's wrong...
Answered by DrBob222
Two ways to do it but both actually are the same.
k=0.693/t<sub>1/2</sub>
Substitute k into the equation below.
ln(12/N) = kt
Solve for N. I get 0.375 g.

Second way:
1/(2<sup>n</sup>)* 12
[1/2<sup>(40/8)</sup>]*12 = ??
Again, 0.375g.