Question

A fresh sample 1311 was left out on the benchtop for 40 days. The scientist forgot it has a half-life of 8 days. The original sample mass

was 64 g. How much of the parent isotope is left?
g

Answer 1

2 g of the parent isotope is left.

Step-by-step explanation:

The half-life of a radioactive isotope is the amount of time it takes for half of the isotope to decay. In this case, the half-life of the isotope is 8 days, which means that after 8 days, half of the isotope will have decayed.

To determine how much of the parent isotope is left after 40 days, we need to calculate how many half-lives have passed in that time. Since the half-life is 8 days, and 40 days have passed, we can divide 40 by 8 to find the number of half-lives that have occurred: 40 / 8 = 5

Since 5 half-lives have passed, we can calculate the amount of the parent isotope that is left by multiplying the original amount of the isotope by 1/2 to the power of the number of half-lives that have passed: 64 * (1/2)^5 = 64 * (1/32) = 2 g

Therefore, after 40 days, only 2 g of the parent isotope is left.