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Potassium-42 has a half-life of 12.4 hours How much of a 745 g sample will be left after 74.4 hours?
To determine how much of the 745 g sample of Potassium-42 will remain after 74.4 hours, we first calculate the number of half-lives that have passed. Since the half-life is 12.4 hours, we divide 74.4 hours by 12.4 hours, which gives us 6 half-lives. After each half-life, the amount remaining is halved, so after 6 half-lives, the remaining mass is ( 745 , \text{g} \times \left(\frac{1}{2}\right)^6 = 745 , \text{g} \times \frac{1}{64} \approx 11.64 , \text{g} ).
How many half-lives will it take for all but 25 percent of the original C-14 to decay?
39
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 secondsAfter 1 half-life: 16*(1/2) = 8 g remainsAfter 2 half-lives: 8*(1/2) = 4g remainsAfter 3 half-lvies: 4*(1/2) = 2g remainsAfter 4 half-lives: 2*(1/2) = 1g remainsSo 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-ktwhere 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 secSubstitute 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-237kln (1/16) = ln (e-237k)-2.7726 = -237kk = -2.7726/-237 = 0.011699 sec-1t1/2 = ln 2/k = 0.693147/0.011699 sec-1t1/2 = 59.25 sec
How much Cu 61 half life about 3 hours would remain from a 2mg sample after 9 hours?
The half-life of Cu-61 is approximately 3 hours, meaning that after each half-life, half of the remaining sample decays. After 9 hours, which is three half-lives (3 hours x 3 = 9 hours), the original 2 mg sample would have gone through three decay cycles. Thus, the amount remaining would be (2 , \text{mg} \times \left(\frac{1}{2}\right)^3 = 2 , \text{mg} \times \frac{1}{8} = 0.25 , \text{mg}).
What approximate amount of the element remains after 3 half-lives have elapsed?
1/8 amount of the element will reamain. After 1 half-life there is 1/2 left After the 2nd half-life there is 1/2 of 1/2 left which is 1/4 After the 3rd half-life there is 1/2 of 1/4 left which is 1/8
How much of a 400-gram sample of K40 is left after 2 half-lives?
After the first half-life, you will have one half of the starting amount. After a second half-life period, you'll be down to one quarter. Of the part that radioactively decays, about 11% of it will decay to 40Ar, and the remainder to 40Ca. Of your total sample of ordinary potassium, only 0.012% will be 40K. The half-life of 40K is about 1.3x109 years.
What fraction of a radioactive sample decays after three half lives?
If I take a radioactive sample of 400 moles of an unknown substance and let it decay to the point of three half-lives I would have 50 moles left of the sample. 1/2 of what is left will decay in the next half-life. At the end of that half-life I will have 25 moles left of the unknown substance or 4/25.
How much cesium is left after 4 half-lives?
1/16 of the original sample of any unstable element remains after 4 half lives.
A 100 gram sample of a radioactive element is present at 9 a.m. on Monday and only 25 grams of the element can be detected at 9 a.m. on Friday. What is the half-life of the source?
The half-life is 2 days. You start with 100 grams. In one half life, you will lose 50 grams and have 50 grams remaining. In a second half-life, you will lose 25 of the 50 grams and have 25 grams left. You will have lost 75 grams of a 100 gram sample of radioactive material and have only 25 grams of it left after two half-lives. That means there are two half-lives from 9 a.m. Monday to 9 a.m. Friday. That's 4 days for 2 half-lives, or 2 days for one half-life.
The half-life of an isotope is the time required for half the nuclei in a sample to?
Half-life is the length of time required for half the atoms in a radioactive sample to decay to some other type of atom. It is a logarithmic process, i.e. in one half-life, there is half the sample left, in two half-lives there is one quarter the sample left, in three half-lives there is one eight left, etc. The equation is... AT = A0 2 (-T/H) ... where A is activity, T is time, and H is half-life.
Radioactive iodine-131 has a half-life of eight days. The amount of a 200.0 gram sample left after 32 days would be -?
12.5 g
How much of the original sample will be left at the end of the second day if a sample of radioactive isotope has a half life of 1 day?
Hi, Each half-life means the mass of the sample has decreased by 1/2 its mass. Thus; After 1 half-life, 1/2 the sample has decayed. After 2 half-lives 3/4 of the sample has decayed. Hope this helps.
A radioactive sample has a half-life of 5.0 min What fraction of the sample is left after 20 min?
After 20 minutes, there have been 4 half-lives (20 min / 5 min per half-life). Each half-life reduces the sample by half, so the fraction of the sample left after 20 minutes is (1/2)^4, which is 1/16. Therefore, 1/16 of the original sample is left after 20 minutes.
How many half-lives have passed if 12.5 of a radioactive sample are left?
3 At the end of the first half life, there will theoretically be 50% remaining. 2 half lives: 25% 3 half lives:12.5 %
A sample of radioactive isotope has a halflife of 1 day how much of the original sample will be left at the end of the fourth day?
If a sample of radioactive material has a half-life of one week the original sample will have 50 percent of the original left at the end of the second week. The third week would be 25 percent of the sample. The fourth week would be 12.5 percent of the original sample.
If the half-life of a radionuclide is 1 month is a sample of it completely decayed after 2 months?
No, it is not. If a radionuclide has a half-life of 1 month, half is gone after 1 month. Half of the half that is left will be gone after 2 months, and that will leave 1/4th of the original amount left after the second month.
Chaser-381 has a half life of 2 days if you start with 8 grams of chaser-381 how much would you have left after eight days?
Eight days would be four half-lives. One-half to the fourth power is one-sixteenth. So you would have half a gram left.
