# Chemistry

posted by .

A 1.00x10-6g sample of nobelium- 254, has a half-life of 55 seconds after it is formed. What is the percentage of nobelium-254 remaining at the following times?
(a) 5.0 min after it forms
(b) 1.0 h after it forms

• Chemistry -

k = 0.693/half life.
Calculate k. Then,
ln(No/N) = kt
No = 1E-6
Solve for N.
k from above.
Plug in t in seconds if youu ue 55 sec to calculte half life.
Convert to percent
Post your work if you get stuck.

• Chemistry -

A)
K=.693/55sec =1.26xE-2
N=e^-3.73*1E-6
N=2.28E-8
%=N/No*100=2.28%

B)
Nt=1E-6* e ^(-(.693/55)*3600 sec)
= 1.984E-26/1E-6*100
%. 2E-18%
Very small number!! I've done it 3 times?

• Chemistry -

I agree with your numbers. Yes, B is a small number but think about it. (a) you didn't have but a microgram initially which is small at the beginning. With a half life of 55 sec (approx 1 min) you have gone through about 60 half lives in 1 hour which leaves very little from the very little you had initially.

• Chemistry -

## Similar Questions

1. ### Chemistry

Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years?
2. ### Chemistry

Consider a certain type of nucleus that has a half life of 32 min. Calculate the percent of original sample of nucleus remaining after 3.0 hours have passed?
3. ### chemistry

the half-life of polonium-218 is 3.0 minutes. what percentage of the original sample remains after 4 half-lives?
4. ### Physcis 30

Q1) If there are 100 radioactive atoms with a half-life of 30 seconds, how many radioactive atoms will remain after one half-life (30 seconds)?
5. ### chemistry

What percent of the original sample of strontium-90 (half-life = 28.9 years) will remain after the following time periods?
6. ### Chemistry

24.0 mL of a 2.4 M silver nitrate is mixed with 32.0 mL of 2.0 M sodium. Calculate the mass of precipitae formed. Calculate the concentration of all ions remaining in solution after the precipitate forms. I don't know how to start …
7. ### Algebra ASAP

The half-life of krypton-91 ^(91Kr) is 10 seconds. At time t = 0 a heavy canister contains 6 g of this radioactive gas. (a) Find a function m(t) = m02^−t/h that models the amount of ^(91)Kr remaining in the canister after t seconds. …
8. ### chem

The half-life of the Nobelium isotope No^257 is about 23 seconds. 644 seconds (or 28 half-life periods) after the isotope was released there were 20 grams remaining. The number of grans of No^257 after h half life periods is M= 20 …
9. ### Chemistry

Technetium-99m, an important radionuclide in medicine, has a half-life of 6.0 hours. What percentage of a sample of technetium-99m will remain undecayed after the following times?
10. ### Chemistry

A substance undergoes a first-order decomposition. After 40.0 min at 500 degrees C, only 12.5% of the original sample remains. What is the half-life of the decomposition?

More Similar Questions