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A 4.5 gram sample of Radon-222 had a half-life of 3.8 days. How many grams of radon...

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dareg17 | Student, Grade 10 | (Level 1) Honors

Posted February 1, 2012 at 10:09 AM via web

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A 4.5 gram sample of Radon-222 had a half-life of 3.8 days. How many grams of radon will remain after 15.3 days?

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txmedteach | High School Teacher | (Level 3) Associate Educator

Posted February 1, 2012 at 10:25 AM (Answer #1)

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Alright, so let's figure out what it means to have a half life of 3.8 days.

It means that after each set of 3.8 days, half of the previous amount of Radon-222 will remain.

To put this into equation form, we recognize that after the 2nd set of 3.8 days, 1/4 of our original amount will remain. After the 3rd set of days, 1/8 will remain. This leads us to the equation:

m(t) = m_0 * (1/2)^(t/3.8)

Where t is the time in days, m_0 is the initial mass, and m(t) is the mass after time (t).

So, let's fill in the numbers we got from the relation above:

m(15.3) = 4.5 * (1/2)^(15.3/3.8)

Well, we don't have to solve for anything. We just need to evaluate the expression on the right! Putting it into the calculator:

m(15.3) = 0.276 g

Therefore, after 15.3 days, we'll have 0.276 grams.

I hope that helps!

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