Question

An unknown radioactive substance has a half-life of 3.20 hours . If 16.5 g of the substance is currently present, what mass A0 was present 8.00 hours ago

Answer 1

the amount present 8 hours ago is Ao = 93.338 g

Step-by-step explanation:

the radioactive decay is given by

A = Ao * 2^(- t/T)

where T = half-life of the substance , t= time , A= amount of substance at time t , Ao= amount of substance at time 0

therefore at t=8 hours , A=16.5 gr

Ao = A*2^(t/T) = 16.5 g * 2^(8 hours/3.20 hours) = 93.338 g

Ao = 93.338 g