Chapter 13: Radioactive decay calculations

58 billion years

A rock sample has .05 million atoms left of a radioactive element. Approximately old is this rock?

42 billion years

A rock sample has .12 million atoms left of a radioactive element. Approximately old is this rock?

12 billion years

A rock sample has .5 million atoms left of a radioactive element. Approximately old is this rock?

17,100 years

A rock sample has 12% of its original carbon-14 remaining. Approximately old is this rock?

28,500 years

A rock sample has 2% of its original carbon-14 remaining. Approximately old is this rock?

5,700 years

A rock sample has 50% of its original carbon-14 remaining. Approximately old is this rock?

4.00 days

After 24.0 days, 2.00 milligrams of an original 128.0 milligram sample remain. What is the half-life of the sample?

4.98 g

At time zero, there are 10.0 grams of W-187. If the half-life is 23.9 hours, how much will be present at the end of one day?

5,700 years

Based on this graph, what is the half life of carbon-14 (the time it takes for half of its radioactive material to decay)?

12 billion years

Based on this graph, what is the half of the element depicted on the graph (the time it takes for half of its radioactive material to decay)?

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?

53.4 days

How long will it take for a 40.0 gram sample of I-131 (half-life = 8.040 days) to decay to 1/100 its original mass?

24.52 years

How much time will be required for a sample of H-3 to lose 75% of its radioactivity? The half-life of tritium is 12.26 years.

8.75 g

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?

1.28 x 1022 atoms

Pd-100 has a half-life of 3.6 days. If one had 6.02 x 1023 atoms at the start, how many atoms would be present after 20.0 days?

12.5 g

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?

1.36 g

U-238 has a half-life of 4.46 x 109 years. How much U-238 should be present in a sample 2.5 x 109 years old, if 2.00 grams was present initially?

155.6 hours

100.0 grams of an isotope with a half-life of 36.0 hours is present at time zero. How much time will have elapsed when 5.00 grams remains?