Name______________________________
Period__________
Date________________
ChemA Chapter 21 Nuclear Chemistry
Half-Life: Power Point Notes
1. What is the definition of half-life?
2. What determines the rate of decay?
3. After one half-life, what percentage of the sample remains?
_________________
4. After two half-lives, what percentage of the sample remains?
_________________
5. After three half-lives, what percentage of the sample remains? _________________
6. After four half-lives, what percentage of the sample remains?
_________________
7. Does the isotope ever decay completely?
8. What problems arise because of this?
Half-life Problems
1.
After one half-life, how many grams of a radioisotope remain if the original sample was
100 grams?
2.
After one half-life, how many grams of a radioisotope remain if the original sample was
50 grams?
3.
After one half-life, how many grams of a radioisotope remain if the original sample was
10 grams?
4.
After three half-lives, how many grams of a radioisotope remain if the original sample
was 100 grams?
5.
After three half-lives, how many grams of a radioisotope remain if the original sample
was 50 grams?
6.
How much of a 100 gram sample of Gold – 198 is left over after 8.10 days if its half-life
is 2.70 days? (12.5 g)
7.
The half-life of Potassium-42 is 12.4 hours. How much of a 750 gram sample is left after
62.0 hours? (23.4g)
8.
A 50 gram sample of Nitrogen-16 decays to 12.5 grams in 14.4 seconds. What is its halflife? (7.2 sec)
9.
Strontium-90 has a half-life of 28.8 years. How long will it take for a 5 gram sample to
decay to 0.3125 grams? (115.2 years)
10.
Phosphorous-32 has a half-life of 14.3 days. A 30 gram sample is stored for 114.4 days.
How much of the original sample remains? (0.117 g)
11.
There are 5.0 grams of Iodine-131 left after 40.35 days. How many grams were in the
original sample if its half-life is 8.07 days? (160 g)
12.
Germanium – 66 has a half-life of 2.5 hours. After 10 hours, if only 25 grams remains,
what was the mass of the original sample? (400 g)