# Half Life Practice

```Honors PS Chemistry Chapter 18
Name_______________________Period____
Half-life Practice Worksheet
Complete the following problems. Please show your work. You may use a table to guide your thought process.
Table:
Time
Half-Life
# atoms remaining (or grams)
1. How many days does it take for 16 g of palladium-103
to decay to 8.0 g? The half-life of palladium-103 is 17
days.
2. 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?
3. What is the half-life of a 100.0 g sample of nitrogen16 that decays to 12.5 g of nitrogen-16 in 21.6 s?
4. If 100.0 g of carbon-14 decays until only 25.0 g of
carbon is left after 11 460 y, what is the half-life of
carbon-14?
5. A 208 g sample of sodium-24 decays to 13.0 g of
sodium-24 within 60.0 h. What is the half-life of this
% of atoms remaining
6. After 42 days a 2.0 g sample of phosphorus-32
contains only 0.25 g of the isotope. What is the halflife of phosphorus-32?
7. In 5.49 seconds, 1.20 g of argon-35 decay to leave
only 0.15 g. What is the half-life of argon-35?
8. 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?
9. Sodium-24 has a half-life of 15 hours. How much
sodium-24 will remain in an 18.0 g sample after 60
hours?
10. Carbon-14 has a half-life of 5730 years. How “old”
would a real fossil be after 4 carbon-14 half-lives?
Complete the following problems. Please show your work. Use the exponential decay function as shown below.
t = elapsed time
( )t/T
T = half-life
11. The half-life of
is 32 minutes. How much of a
16.0 gram sample of this isotope will remain at the
end of 3.0 hours?
13. The half-life of
is 9.0 x 106 years. How much of
a 1.0-g sample of this isotope will remain at the end
of 40.0 million years?
12. The isotope strontium-90 is produced during the
testing of nuclear weapons. If 100.0 mg of
strontium-90 was released in the atmosphere in
1960, how much of the radioisotope remains 85
years later? The half-life of strontium-90 is 29 years.
14. The radioisotope technetium-99 is often used as a
radiotracer to detect disorders of the body. It has a
half-life of 6.01 hours. If a patient received a 25.0mg dose of this isotope during a medical procedure,
how much would remain 48.0 hours after the does
was given?
Multiple Choice: Choose the letter of the best answer, and write it in the blank.
_____15. If the half-life of Radon-222 is 3.8 days, how much of a 100.0 mg sample will remain after 3.8 days?
a.) 100.0 mg
b.) 50.00 mg
c.) 25.00 mg
d.) 12.50 mg
e.) 6.250 mg
f.) None of the preceding
_____16. If the half-life of Radon-222 is 3.8 days, how much of a 100.0 mg sample will remain after 7.6 days?
a.) 100.0 mg
b.) 50.00 mg
c.) 25.00 mg
d.) 12.50 mg
e.) 6.250 mg
f.) None of the preceding
_____17. If the half-life of Radon-222 is 3.8 days, how much of a 100.0 mg sample will remain after 15.2 days?
a.) 100.0 mg
b.) 50.00 mg
c.) 25.00 mg
d.) 12.50 mg
e.) 6.250 mg
f.) None of the preceding
_____18. If the half-life of Radon-222 is 3.8 days, how much of a 100.0 mg sample will remain after 22.8 days?
a.) 100.0 mg
b.) 50.00 mg
c.) 25.00 mg
d.) 12.50 mg
e.) 6.250 mg
f.) None of the preceding
_____19. If the half-life of Phosphorus-32 is 14.28 days, how much of a 38.2 g sample will remain after 2 half-lives?
a.) 38.2 g
b.) 9.55 g
c.) 4.78 g
d.) 1.19 g
e.) 0.597 g
f.) None of the preceding
_____20. If the half-life of Phosphorus-32 is 14.28 days, how much of a 38.2 g sample will remain after 42.84 days?
a.) 38.2 g
b.) 9.55 g
c.) 4.78 g
d.) 1.19 g
e.) 0.597 g
f.) None of the preceding
_____21. If the half-life of Phosphorus-32 is 14.28 days, how much of a 38.2 g sample will remain after 4 half-lives?
a.) 38.2 g
b.) 9.55 g
c.) 4.78 g
d.) 1.19 g
e.) 0.597 g
f.) None of the preceding
_____22. If the half-life of Phosphorus-32 is 14.28 days, how much of a 38.2 g sample will remain after 85.68 days?
a.) 38.2 g
b.) 9.55 g
c.) 4.78 g
d.) 1.19 g
e.) 0.597 g
f.) None of the preceding
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