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What is the halflife of sodium 25 if 1.00 gram of a 16.00 gram sample of sodium 25 remains unchanged after 237 seconds?
59.25 seconds
After 1 half-life: 16*(1/2) = 8 g remains
After 2 half-lives: 8*(1/2) = 4g remains
After 3 half-lvies: 4*(1/2) = 2g remains
After 4 half-lives: 2*(1/2) = 1g remains
So after 4 half-lves you have 1 gram of Na25 left. This is also the amount remaining after 237 seconds. Since 4 half-lives have elapsed over 237 seconds, you can divide 237 seconds by 4 to find the half-life of Na25 is 59.25 seconds.
You can also figure it out using the rate of decay formula:
At = Ao*e-kt
where Ao is the initial amount, At is the amount left after some time t. k is the decay constant which is k = ln 2 / t1/2 where t1/2 is the half-life.
In this case Ao = 16g, At = 1g, t=237 sec
Substitute in the formula to solve for k, then take the answer for k and use it in the other formula to solve for the half-life (t1/2):
1 = 16*e-237k
ln (1/16) = ln (e-237k)
-2.7726 = -237k
k = -2.7726/-237 = 0.011699 sec-1
t1/2 = ln 2/k = 0.693147/0.011699 sec-1
t1/2 = 59.25 sec
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a sample is a sample sized piece given... a sample size is the amount given in one sample
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What is the difference between a sample and sampling?
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2
Which fraction of an original 20.00-gram sample of nitrogen-16 remains unchanged after 36.0 seconds?
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What part of a radioactive sample remains unchanged after 2 half lives?
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What fraction of a sample of N 16 remains undecayed after 43.2 seconds?
1.5% remains after 43.2 seconds.
If Astatine-218 has a half-life of 1.6 s Suppose you have a 1.2-g sample of astatine-218 How much of the sample remains unchanged after 6.4 seconds Explain how you solved the problem?
After 6.4 seconds, there would be 0.3g of the original sample of Astatine-218 remaining unchanged. This is calculated by dividing the time elapsed by the half-life to determine the number of half-lives passed (6.4 s ÷ 1.6 s = 4 half-lives), then using this to calculate the remaining amount (1.2 g ÷ 2^4 = 0.3 g).
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What is the time needed for half of a sample of a radioactive isotope to break down to form daughter isotopes called?
halflife
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Thorium-234 has a half-life of 24.1 days. How much of a 100-g sample of thorium-234 will be unchanged after 48.2 days?
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How much of a 100 g sample of thorium 234 will be unchanged after 48.2 days?
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How many unchanges atoms would remain after 3 half lives if the initial sample had 600 unchanged atoms?
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Is a radioactive sample has decayed until only one eighth of the original sample remains unchanged how many half lives have elapsed?
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