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Topic 12: Nuclear Chemistry
18. Half-life problems: Determining half-life
1. What is the half-life of Nitrogen–16?
1) 16 s 2) 17.2 s 3) 7.2 s 4) 19 s
2. A radioisotope undergoes 2 half-life periods in 180 ms. What is the half life of this radioisotope?
1) 90 ms
4) 180 ms
3) 2 ms
2) 360 ms
3. In 6.20 h, a 100 gram sample of Ag-112 decays to 25.0 gram. What is the half-life of Ag-112?
1) 1.60 h 2) 3.10 h 3) 6.20 h 4) 12.4 h
4. What is the half-life of Na if 1.00 grams of a 16.00 grams sample of Na remains unchanged after
25
25
237 seconds?
Teacher Preview Copy
Teacher Preview Copy
1) 47.4 s 2) 59.3 s 3) 79.0 s 4) 118 s
5. After 32 days, 5 milligrams of an 80-gram sample of a radioactive isotope remains unchanged. What
is the half-life of this element?
1) 8 days 2) 16 days 3) 4 days 4) 2 days
6. A radioactive isotope of an element decays from 20 grams to 5 grams in 8 minutes. What is the half-
life of this radioisotope?
1) 15 minutes 2) 20 minutes 3) 10 minutes 4) 4 minutes
19. Half-life: Determining remaining mass
1. What is the total mass of a 50 grams sample of a radioisotope remaining after 3 half-life periods?
1) 150 grams 2) 12.5 grams 3) 6.25 grams 4) 16.7 grams
2. How many grams of a 120 grams sample of cobalt-60 will remain after 2 half-life periods?
1) 60 grams 2) 30 grams 3) 240 grams 4) 2 grams
3. What amount of a 48 g sample of K-37 will remain after 5 half-life periods?
1) 1.5 g 2) 3.0 g 3) 5.1 g 4) 6.0 g
4. What is the mass of a 60.0 gram sample of N-16 remaining unchanged after 28.8 seconds?
4) 3.75 g
2) 15.0 g
3) 7.50 g
1) 30.0 g
60
5. What total mass of a 32 g sample of Co will remain unchanged after 21.16 years?
1) 1.0 g 2) 2.0 g 3) 4.0 g 4) 8.0 g
6. Approximately how many grams of a 50 g sample of radium-226 will remain unchanged after 6400
years?
1) 25 g 2) 128 g 3) 6.25 g 4) 3.13 g
7. A radioisotope of element X has a half-life of 1.5 days. How many grams of a 5 gram sample of this
isotope will remain unchanged after 3.0 days?
1) 1.25 grams 2) 2.5 grams 3) 7.5 grams 4) 4.5 grams
8. The half-life of a radioisotope is 20.0 minutes. What is the total amount of a 10 g sample of this
isotope remaining after 1 hour minutes?
1) 5.00 g 2) 3.33 g 3) 2.50 g 4) 1.25 g
350 Copyright © 2010 E3 Scholastic Publishing. All Rights Reserved. Survivingchem.com
Topic 12: Nuclear Chemistry
18. Half-life problems: Determining half-life
1. What is the half-life of Nitrogen–16?
1) 16 s 2) 17.2 s 3) 7.2 s 4) 19 s
2. A radioisotope undergoes 2 half-life periods in 180 ms. What is the half life of this radioisotope?
1) 90 ms
4) 180 ms
3) 2 ms
2) 360 ms
3. In 6.20 h, a 100 gram sample of Ag-112 decays to 25.0 gram. What is the half-life of Ag-112?
1) 1.60 h 2) 3.10 h 3) 6.20 h 4) 12.4 h
4. What is the half-life of Na if 1.00 grams of a 16.00 grams sample of Na remains unchanged after
25
25
237 seconds?
Teacher Preview Copy
Teacher Preview Copy
1) 47.4 s 2) 59.3 s 3) 79.0 s 4) 118 s
5. After 32 days, 5 milligrams of an 80-gram sample of a radioactive isotope remains unchanged. What
is the half-life of this element?
1) 8 days 2) 16 days 3) 4 days 4) 2 days
6. A radioactive isotope of an element decays from 20 grams to 5 grams in 8 minutes. What is the half-
life of this radioisotope?
1) 15 minutes 2) 20 minutes 3) 10 minutes 4) 4 minutes
19. Half-life: Determining remaining mass
1. What is the total mass of a 50 grams sample of a radioisotope remaining after 3 half-life periods?
1) 150 grams 2) 12.5 grams 3) 6.25 grams 4) 16.7 grams
2. How many grams of a 120 grams sample of cobalt-60 will remain after 2 half-life periods?
1) 60 grams 2) 30 grams 3) 240 grams 4) 2 grams
3. What amount of a 48 g sample of K-37 will remain after 5 half-life periods?
1) 1.5 g 2) 3.0 g 3) 5.1 g 4) 6.0 g
4. What is the mass of a 60.0 gram sample of N-16 remaining unchanged after 28.8 seconds?
4) 3.75 g
2) 15.0 g
3) 7.50 g
1) 30.0 g
60
5. What total mass of a 32 g sample of Co will remain unchanged after 21.16 years?
1) 1.0 g 2) 2.0 g 3) 4.0 g 4) 8.0 g
6. Approximately how many grams of a 50 g sample of radium-226 will remain unchanged after 6400
years?
1) 25 g 2) 128 g 3) 6.25 g 4) 3.13 g
7. A radioisotope of element X has a half-life of 1.5 days. How many grams of a 5 gram sample of this
isotope will remain unchanged after 3.0 days?
1) 1.25 grams 2) 2.5 grams 3) 7.5 grams 4) 4.5 grams
8. The half-life of a radioisotope is 20.0 minutes. What is the total amount of a 10 g sample of this
isotope remaining after 1 hour minutes?
1) 5.00 g 2) 3.33 g 3) 2.50 g 4) 1.25 g
350 Copyright © 2010 E3 Scholastic Publishing. All Rights Reserved. Survivingchem.com
