The half-life of Erbium-165 is 10.4 hours. After 24 hours a sample has been reduced to a mass of 2 mg. What was the initial mass of the sample, and how much will remain after 3 days?

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Question:

The half-life of Erbium-165 is 10.4 hours. After 24 hours a sample has been reduced to a mass of 2 mg. What was the initial mass of the sample, and how much will remain after 3 days?

Answer:

Answer:

?f=%5BA 0%5D%3D10%5C%20mg

?f=%5BA t%5D%3D0

Explanation:

Given that:

Half life = 10.4 hours

?f=t %7B1%2F2%7D%3D%5Cfrac%7B%5Cln2%7D%7Bk%7D

Where, k is rate constant

So,  

?f=k%3D%5Cfrac%7B%5Cln2%7D%7Bt %7B1%2F2%7D%7D

?f=k%3D%5Cfrac%7B%5Cln2%7D%7B10

The rate constant, k = 0.06664 hour⁻¹

Time = 24 hours

Using integrated rate law for first order kinetics as:

?f=%5BA t%5D%3D%5BA 0%5De%5E%7B kt%7D

Where,  

?f=%5BA t%5D is the concentration at time t  = 2 mg

?f=%5BA 0%5D is the initial concentration = ?

?f=2%5C%20mg%3D%5BA 0%5D%5Ctimes%20e%5E%7B 0

Now, time = 3 days = 3*24 hours = 72 hours ( 1 day = 24 hours)

Thus,

?f=%5BA t%5D%3D10%5Ctimes%20e%5E%7B 0.06664%5Ctimes%2072%7D%5C%20mg%3D0

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