Chemistry

For my homework the question is...
What is the half life of polonium 214 if a 1 gram sample decays to 31.25mg after 820 seconds? Im not sure how you arrive at the answer, my friend says the answer is 5 but were not sure how to do it..thanks for any help u may have

ln(No/N)= kt
No = 1 gram
N = 0.03215 g
t = 820 seconds.
solve for k. THEN
k=0.693/t1/2

.03125g=1g * e^(-.692*820sec/thl)

where thl is halflife time.

thl*ln .03125 = -.692*820

thl= -.692*820/ln.03125

Check you friend:
1g
1/2g
1/4 g
1/8g
1/16g
1/32g=.0312sec
So you friend is right, it takes 5 half lives, or 820/5 seconds. Check that with the answer above.

Your friend is correct that it goes through 5 half-lives BUT the question is what is the half-life, not how many half-lives it goes through.

My equation or the one Bob Pursley gave you will give you t1/2

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