__Half-Life Practice
Problems__

1.) What is the
half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 grams in 21.6
seconds?

2.) All isotopes of
technetium are radioactive, but they have widely varying half-lives. If an
800.0 gram sample of

technetium-99
decays to 100.0 g of technetium-99 in 639,000 years, what is its half-life?

3.) A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0
hours. What is the half-life of this

radioactive isotope?

4.) If the half-life
of iodine-131 is 8.10 days, how long will it take a 50.00 g sample to decay to
6.25 g?

5.) The half-life of
hafnium-156 is 0.025 seconds. How long will it take a 560 g sample to decay to
one-fourth

of its original mass?

6.) Chromium-48 has
a short half-life of 21.6 hours. How long will it take 360.00 g of chromium-48
to decay

to 11.25 g?

7.) Potassium-42 has
a half-life of 12.4 hours. How much of an 848 g sample of potassium-42 will be
left after

62.0 hours?

8.) Carbon-14 has a
half-life of 5730 years. How much of a 144 g sample of carbon-14 will remain
after

1.719 × 10^{4} years?

9.) If the half-life
of uranium-235 is 7.04 × 10^{8} years and 12.5 g of uranium-235 remain
after 2.82 × 10^{9} years,

how much of the radioactive isotope
was in the original sample?