alexwright817
alexwright817 alexwright817
  • 23-10-2016
  • Chemistry
contestada

A radioactive isotope has a half-life of 2.5 years. Which fraction of the original mass remains unchanged after 10 years?

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syed514
syed514 syed514
  • 04-11-2016
Using the following equation. 

A = Ao (1/2) ^n 
n = 4 
A = Ao (1/2)^4
   = 1/16
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Dejanras
Dejanras Dejanras
  • 04-01-2019

Answer is: 1/16 of the original mass remains unchanged after 10 years

Take 100 atoms:

After first half-life (2.5 years): 50% · 100 ÷ 100% = 50 or 1/2.  

After second half-life (5 years): 0.5 · 50 = 25 or 1/4.  

After third half-life (7.5 years): 0.5 · 25 = 12.5 or 1/8.  

After fourth half-life (10 years): 0.5 · 12.5 = 6.25 or 1/16.

6.25 ÷ 100 · 100% = 6.25% or 1/16.

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