Posted by **Noah** on Sunday, February 19, 2012 at 5:08pm.

Uranium-238 decays to Lead-206. The half life of Uranium-238 is 4.5 billion years. If you have a 100 g sample. How much sample will you have after 2 half lifes?

- Half-Life -
**Reiny**, Sunday, February 19, 2012 at 5:18pm
just do it in your head ...

after 1 half-life you would have 50 g left

after 2 half-lifes you would have 25 g left

- Half-Life -
**DrBob222**, Sunday, February 19, 2012 at 6:13pm
Your question isn't quite clear to me. If you want the mass of U after two half lives, then 25 g is correct. If you want the mass of sample left after two half lives, that is 25g U + the equivalent of 75 g U that's been converted to Pb. That conversion is 75 g U x (atomic mass Pb/atomic mass U) = about 75*207/238 = about 65 g. Therefore, the total mass is 25 + about 65 = about 90 g.

- Half-Life -
**Dee**, Friday, March 22, 2013 at 11:11pm
If the half-life of a radionuclide is 1 month, is a sample of it completely decayed after 2 months?

## Answer This Question

## Related Questions

- geology - How old are the oldest meteorites yet studied and what is the minimum ...
- Chemistry - Uranium-238 has half life of 4.51 * 10^9 years Uranium-234 has half ...
- Chemistry - Geologists can estimate the age of rocks by their uranium-238 ...
- Chemistry 1046 - Geologists can estimate the age of rocks by their uranium-238 ...
- Chem 2 - The half-life for the radioactive decay of U-238 is 4.5 billion years ...
- Chemistry *URGENT* - URGENT help! 3. A rock sample was dated using potassium-40...
- Chemistry - The half-life for the process 238 U --> 206 Pb is 4.5*10^9 yr. A ...
- algebra - The half-life of 234U, uranium-234, is 2.52 105 yr. If 97.7% of the ...
- math - The half-life of 234U, uranium-234, is 2.52 105 yr. If 98.3% of the ...
- algebra - The half-life of 234U, uranium-234, is 2.52 105 yr. If 98.4% of the ...

More Related Questions