9th Edition
Steven S. Zumdahl
ISBN: 9781133611097




9th Edition
Steven S. Zumdahl
ISBN: 9781133611097
Textbook Problem

Iodine-131 has a half-life of 8.0 days. How many days will it take for 174 g of 131I to decay to 83 g of 131I?

Interpretation Introduction


Half life of Iodine- 131 is given. Number of days taken by 174g of 131I to decay to 83g of 131I is to be calculated.

Concept introduction:

  • In radioactive decay, the decomposition of a parent nuclide takes place and a new daughter nuclide is formed.
  • Decay constant is the quantity that expresses the rate of decrease of number of atoms of a radioactive element per second.
  • Half life of radioactive sample is defined as the time required for the number of nuclides to reach half of the original value.


The value of t1/2 is 8days .

The decay constant is calculated by the formula given below.



  • t1/2 is the half life of nuclide.
  • k is decay constant.

Substitute the value of half life in the above formula.

k=0.6938days-1=0.086625days-1_ .

The decay constant is 0.086625days-1_ .


The value of initial amount is 174g

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