Question

A radioactive sample initially contains 2.40 × 10−2 mol of a radioactive material whose half-life is 6.00 h. How many moles of the radioactive material remain after 6.00 h? After 12.0 h? After 36.0 h? 

Answer 1

number of moles remaining, $N=N_0(1/2)^{T/t}$

number of moles remaining after 6h$=2.4\times 10^{-2}(1/2)^{6/6}=0.012moles$

number of moles remaining after 12h$=2.4\times10^{-2}(1/2)^{12/6}=0.006moles$

number of moles remaining after 36h$=2.4\times10^{-2}(1/2)^{36/6}=3.75\times10^{-4}moles$