Practice Half-Life in Chemistry
Use these practice problems to test your method after reviewing the concept explanation and worked examples.
Quick Recap
Half-life is the time required for half of the radioactive nuclei in a sample to decay.
Radioactive samples do not lose the same amount each time; they lose the same fraction each time.
Showing a random 20 of 50 problems.
Example 1
easyStarting with of an isotope, how much remains after half-life?
Example 2
mediumHow much of a 1 g sample remains after 5 half-lives, as a fraction?
Example 3
mediumA 500 g sample drops to 62.5 g. How many half-lives passed?
Example 4
easyStarting with 80 g of an isotope, how much remains after one half-life?
Example 5
hardA medical isotope must drop below of injected activity before discharge. If half-life is hours, how long until below ?
Example 6
mediumAn isotope has half-life minutes. Starting with , how many remain after minutes?
Example 7
easyAn isotope with half-life days starts at . How much remains after days?
Example 8
easyDoes temperature change the half-life of a radioactive isotope?
Example 9
easyIf decays to , how many half-lives passed?
Example 10
mediumA sample of Tc-99m (half-life hours) is administered. How much remains after hours?
Example 11
easyWill a radioactive sample ever reach exactly zero atoms after a finite number of half-lives, in theory?
Example 12
hardIf an isotope has days and you want to have decayed, how long must you wait?
Example 13
mediumIodine-131 has half-life days. Starting from , how much remains after days?
Example 14
easyIf 100 g decays to 25 g, how many half-lives passed?
Example 15
mediumAn isotope's mass drops from to in days. What is its half-life?
Example 16
challengeAn isotope decays via with . Approximate its half-life.
Example 17
easyHow many half-lives have passed when a sample is reduced to of its original amount?
Example 18
easyTrue or False: After half-lives, of the sample remains.
Example 19
hardA sample contains parent and daughter atoms (no daughter initially). How many half-lives have passed (to nearest)?
Example 20
mediumA sample of 320 g has a half-life of 8 days. How much remains after 24 days?