# Thread: Study guide problem Half-lifes!

1. ## Study guide problem Half-lifes!

4. The half-life of lead-209 is 3.3 hours. The initial amount S grams.

a. Express the amoundt of substance S remaining as a function of time t.
b. How mmuch of the substance is left after 3.3 hourse? after 33 hours?
c. Determine S if there is 5 g left after 22 hours.

2. Originally Posted by rlarach
4. The half-life of lead-209 is 3.3 hours. The initial amount S grams.

a. Express the amoundt of substance S remaining as a function of time t.
b. How mmuch of the substance is left after 3.3 hourse? after 33 hours?
c. Determine S if there is 5 g left after 22 hours.
a. Standard formula: $m = m_0 \left( \frac{1}{2} \right)^{\frac{t}{t_{1/2}}}$

where $t_{1/2}$ is the half-life (in hours) and $m_0$ is the initial amount (in gram).

So the answer to a. is ........

b. Sub t = 3.3 and solve for m. Alternatively, note that t = 1 half-life .....
Sub t = 33 and solve for m.

c. Sub m = 5 and t = 22 and solve for S.