Honors Chem
Directions: The following questions involve more practice with radioactive decay half-life. Complete the problems to the best of your ability. This assignment is due by next WEDNESDAY, November 16th.
1. 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? a. Calculate how many half-lives have passed during the decay of the 100.0 g sample.
100 grams/2 50 grams/2 25grams…2 half lives have passed
b. Solve for the half-life.
11,460year/2 half lives = 5,730 years half-life of carbon – 14
2. What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s? 100g50g25g12.5g…3 half lives have passed 21.6s/3 half lives = 7.2 seconds half-life of nitrogen – 16
3. All isotopes of technetium are radioactive, but they have widely varying half-lives. If an
800.0 g sample of technetium-99 decays to 100.0 g of technetium-99 in 639 000 yrs, what is its half-life? 800g/2 400g/2 200g/2 100g…3 half lives have passed 639,000years/3 half lives = 213,000 years half-life of technetium – 99
4. A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 hrs. What is the half-life of this radioactive isotope? 208g/2 104g/2 52g/2 26g/2 13g…4 half lives have passed 60hrs/4 half lives = 15hrs half-life of sodium – 24
5. Thallium-208 has a half-life of 3.053 min. How long will it take for 120.0 g to decay to
7.50 g?
a. Calculate how many half-lives have passed during the decay of the 120.0 g sample. 120g/2 60g/2 30g/2 15g/2 7.5g…4 half lives have passed b. Solve for the half-life. 3.053min x 4 half lives = 12.212 min (time taken for Thallium – 208 to decay)
8. 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? 50g/2 25g/2 12.5g/2 6.25g…3 half lives have passed 8.10 days x 3 half lives = 24.3 days
9. The half-life of hafnium-156 is 0.025 s. How
1. 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? a. Calculate how many half-lives have passed during the decay of the 100.0 g sample.
100 grams/2 50 grams/2 25grams…2 half lives have passed
b. Solve for the half-life.
11,460year/2 half lives = 5,730 years half-life of carbon – 14
2. What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s? 100g50g25g12.5g…3 half lives have passed 21.6s/3 half lives = 7.2 seconds half-life of nitrogen – 16
3. All isotopes of technetium are radioactive, but they have widely varying half-lives. If an
800.0 g sample of technetium-99 decays to 100.0 g of technetium-99 in 639 000 yrs, what is its half-life? 800g/2 400g/2 200g/2 100g…3 half lives have passed 639,000years/3 half lives = 213,000 years half-life of technetium – 99
4. A 208 g sample of sodium-24 decays to 13.0 g of sodium-24 within 60.0 hrs. What is the half-life of this radioactive isotope? 208g/2 104g/2 52g/2 26g/2 13g…4 half lives have passed 60hrs/4 half lives = 15hrs half-life of sodium – 24
5. Thallium-208 has a half-life of 3.053 min. How long will it take for 120.0 g to decay to
7.50 g?
a. Calculate how many half-lives have passed during the decay of the 120.0 g sample. 120g/2 60g/2 30g/2 15g/2 7.5g…4 half lives have passed b. Solve for the half-life. 3.053min x 4 half lives = 12.212 min (time taken for Thallium – 208 to decay)
8. 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? 50g/2 25g/2 12.5g/2 6.25g…3 half lives have passed 8.10 days x 3 half lives = 24.3 days
9. The half-life of hafnium-156 is 0.025 s. How