SOLUTION: The Half-Life of palladium-100 is 4 days. After 20 days a sample has been reduced to a mass of .375 grams. What was the initial mass of the sample? What is the mass after 3

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Question 805161: The Half-Life of palladium-100 is 4 days. After 20 days a sample has been reduced to a mass of .375 grams.
What was the initial mass of the sample?
What is the mass after 3 days?
After how many days will only .15 g remain?
Thank you so much!!

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
The Half-Life of palladium-100 is 4 days.
After 20 days a sample has been reduced to a mass of .375 grams.
:
Using the formula: A = Ao*2^(-t/h); where:
A = the resulting amt after t time
Ao = initial amt (t=0)
t = time of decay
h = half-life of the substance
:
What was the initial mass of the sample?
Ao*2^(-20/4) = .375
Ao*2^(-5) = .375
Ao = 1%2F2%5E5 = .375
Ao = 1%2F32 = .375
Ao = .375 * 32
Ao = 12 grams is the initial amt
:
:
What is the mass after 3 days?
A = 12*2^(-3/4)
A = 12*.5946
A = 7.135 grams after 3 days
:
;
After how many days will only .15 g remain?
12*2(-t/4) = .15
2^(-t/4) = .15%2F12
2^(-t/4) = .0125
Using nat logs
-t%2F4 = ln%28.0125%29%2Fln%282%29
-t%2F4 = -6.322
t = -4 * -6.322
t = +25.3 days for only .15 gr to remain