Read the “Rate of Nuclear Decay” section in Chapter 25 of your text. Make sure y
ID: 486485 • Letter: R
Question
Read the “Rate of Nuclear Decay” section in Chapter 25 of your text. Make sure you understand the concept of half-life of a radionuclide.
Suppose you have a radionuclide, A, that goes through a two–step decay sequence, first to B and then to C, which is stable. Suppose also that the half-life from A to B is six days, and the half-life from B to C is one day. Predict by listing in declining order, greatest to smallest, the amounts of A, B, and C that will be present at the end of six days. Explain your prediction.
This is for Chemistry II extra credit, please give as much detail as possible! Thanks!
Explanation / Answer
All nuclides with a half-life are unstable, but the longer a nuclide’s half-life the more stable it is. From the given concept A undergoes two–step decay sequence, first to B and then to C. half-life of A to give B is 6 days and half-life of B to give C is one day. So radioactive nuclide A, is more stable than B and C nuclides.
Order of stability: A> B>C.
Half - life of A is 6 days. The amount of A present at the end of sixth day is given as:
(½)n (here n = number of half-lives = 6/6=1)
Amount of A present at the end of sixth day = 0.5
Half - life of B is one day.
n = 6/1 = 6 half-lives
Amount of B present at the end of sixth day = (½)6 = 0.0156
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