Half-Life Worksheet
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Don’t worry about significant figures; just put what your calculator gives you!
1. Element X has a mass of 300g and a ½ life of 10 years. How many grams will remain after 40
years? Hint: first determine how many ½ lives there are in 40 years.
2. Element Z has a mass of 430g. Scientists determined it to have a ½ life of 5 years. How many
grams of element Z will remain after 15 years?
3. Phosphourous-32 is a radioisotope with a half-life of 14.3 days. If you start with 4 g of
phosphorous-32, how many grams will remain after 57.2 days? How many half-lives will have
passed?
4. Sodium-24 has a half-life of 15 hours. How much sodium-24 will remain in an 18.0-g sample after
60 hours?
5. After 42 days, a 2.0-g sample of phosphorus-32 contains only 0.25 g of isotope. Find the half-life
of phosphorus-32?
6. The half-life of chromium-51 is 28 days. If the sample contained 510 grams, how much Cr-51
would remain after 56 days?
7. If 20.0 g of a radioactive isotope are present at 1:00 PM and 5.0 g remain at 2:00 PM, what is the
half-life of the isotope?
8. A medical institution requests 1 g of bismuth-214, which has a half-life of 20 min. How many
grams of bismuth-214 must be prepared if the shipping time is 2 h?