Question

A 3.6 mole sample of Co-60 has a half-life of 5.2 years. How many moles of Co is left after 20.8 years?

Answer 1

We have 3.6 moles which will decay in half in each 5.2 years, since 20.8/5.2 is equal to 4, we will have 4 decays:

0 years = 3.6 moles

5.2 years = 1.8 moles

10.4 years = 0.9 moles

15.6 years = 0.45 moles

20.8 years = 0.225 moles