Chemistry
CH 21 Half Life
Name ______________________
1. With a half-life of 28.8 yrs, how long will it take for 1 gram of Sr-90 to decay to 125 mg?
(86.4yrs)
2. The half-life of Na-25 is 1.0 minutes. Starting with 1 kg of this isotope, how much will remain
after an hour? (8.7 x10-16g)
3. Co-60 has a half-life of 5.3 yrs. If a pellet that has been in storage for 26.5 yrs contains 14.5 g of
Co-60, how much of this radioisotope was present when the pellet was put into storage? (464 g)
4. What is the half-life of Po-214 if after 820 s, a 1.00g sample decays to 31.25 mg? (164 sec)
5. The half-life of Cs-137 is 30.2 yrs. If the initial mass of a sample is 1.00 kg, how much will remain
after 151 yrs? (31.2 g)
6. Given that the half-life of C-14 is 5730 yrs, consider a sample of fossilized wood that, when alive,
would have contained 24g of C-14. It now contains 1.5 g of C-14. How old is it? (23,000 yrs)
7. A 64 g sample of Ge-66 is left undisturbed for 12.5 hrs. At the end of that period, only 2.0 g
remain. What is the half-life? (2.5 hrs)
8. A 1.000 Kg block of P-32, which has a half-life of 14.3 days, is stored for 100.1 days. At the end of
this period how much P-32 remains in grams? (7.813 g)