Question

the half-life Na-24 is 15 hours. How much of a 400.0g sample will remain after 75spli hours?

Answer 1

Half life: is the time token by the isotope to fall to half its original value.

Given 400 g of Na-24 with half life of 15 hrs

So After 15 hrs - 400/2 = 200 g Na-24

                 after 30 hrs - 200/2 = 100 g Na-24    ( another 15 hrs)

                              after 45 rs - 100/2 = 50g Na-24 ( another 15 hrs)

                                          after 60 hrs - 50/2 = 25 g Na-24 ( another 15 hrs)

                                                     after 75 hrs - 25/2 = 12.5 g Na-24 ( another 15 hrs)

So after 75 hrs, 12.5 g of Na-24 sample is remaining