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home / study / science / chemistry / chemistry questions and answers / 6. if we start with 800 atoms of radioactive substance, how many would remain after (show your ... Question: 6. If we start with 800 atoms of radioactive substance, how many would remain after (show your wo... 6. If we start with 800 atoms of radioactive substance, how many would remain after (show your work in the graph) a. 3 half-lives b. 5 half-lives
7. If a sample known to be about 10,740 years old has 400 carbon-14 atoms, how many atoms were in the original sample when the organism died. The half for carbon -14 is 5730 years.( show your work in the graph).
Explanation / Answer
6.
initial amount of radioactive substance = 800 atoms
a. after 3 half-lives
amount remained = (1/2)^3 x 800 = 100 atoms
a. after 5 half-lives
amount remained = (1/2)^5 x 800 = 25 atoms
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7. decay constant of C-14 (l) = ln(2)/t1/2
= ln(2)/5730 years
= 0.00012 years-1
age of sample (t) = 10,470 years
[C]t = 400 C=14 atoms
[C]o = ? atoms
Using,
ln[C]o = ln[C]t + lt
= ln(400) + 0.00012 x 10,740
initial amount present [C]o = 14051 atoms
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