Half – Life Problems

The half-life of Zn-71 is 2. 4 minutes. If one had 100 The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be left after 7.2 minutes has elapsed? 100 g 2. 50 g 3. 25 g 100 g 1 2.4 50 g 2 4.8 25 g 3 7.2 12.5 g 4. 12.5 g

Os-182 has a half-life of 21. 5 hours. How many grams of a 10 Os-182 has a half-life of 21.5 hours. How many grams of a 10.0 gram sample would have decayed after exactly three half-lives? 10 g 2. 2.5 g 3. 1.25 g 10 1 21.5 5 g 2 43 2.5 g 3 64.5 1.25 g 4. 5 g

After 24. 0 days, 2. 00 milligrams of an original 128 After 24.0 days, 2.00 milligrams of an original 128.0 milligram sample remain. What is the half-life of the sample? 4 128 mg 1 64 mg 2 32 mg 3 16 mg 4 8 mg 5 4 mg 6 24.0 2 mg 2. 2 3. 5 4. 6

1 second 2. 2 seconds 3. 3 seconds 4. 3.34 seconds Fermium-253 has a half-life of 0.334 seconds. A radioactive sample is considered to be completely decayed after 10 half-lives. How much time will elapse for this sample to be considered gone? 1 second 1 .334 2 .668 3 1.002 4 1.336 5 1.67 6 2.004 7 2.338 8 2.672 9 3.006 10 3.34 seconds 2. 2 seconds 3. 3 seconds 4. 3.34 seconds

100.0 grams of an isotope with half-life of 26 hours is present at time zero. How much time will elapse before 50 grams remains? 100 1 26 hrs 50 g 100 g 2. 50 g 3. 26 g 4. 0 g

15.28 days 2. 11.46 day 3. 7.64 days 4 3.82 days Original sample 1 Rn-222 has a half-life of 3.82 days. How long before only 1/16 of the original sample remains? 15.28 days Original sample 1 3.82 1/2 2 7.64 1/4 3 11.46 1/8 4 15.28 1/16 2. 11.46 day 3. 7.64 days 4 3.82 days