A 854.3 ng sample of an unknown radioactive substance was placed in storage and
ID: 1063113 • Letter: A
Question
A 854.3 ng sample of an unknown radioactive substance was placed in storage and its mass measured periodically. After 47 days the amount of radioactive substance had decreased to 106.8 ng. How many half-lives of the unknown radioactive substance have occurred?
A 854.3 ng sample of an unknown radioactive substance was placed in storage and its mass measured periodically. After 47 days the amount of radioactive substance had decreased to 106.8 ng. How many half-lives of the unknown radioactive substance have occurred? Number half. livesExplanation / Answer
use:
[R] = [R]o*e^(-k*t)
106.8 = 854.3*e^(-k*47)
e^(-k*47) = 0.125
k = 0.04424 days-1
half life = 0.693/k
= 0.693 / (0.04424)
= 15.66 days
number of half life = 47/15.66 = 3
Answer: 3
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