Answer:
129 g
Explanation:
The radioactive decay of a substance can be represented through the following expression.
[tex]A=A_{0}.e^{-k.t}[/tex]
where,
A is the amount of A at certain time t
A₀ is the initial amount of A
k is the rate constant
We can find k from the half-life (t1/2) using the following expression.
[tex]t_{1/2}=\frac{ln2}{k} \\k=\frac{ln2}{t_{1/2}} =\frac{ln2}{3.20h} =0.217h^{-1}[/tex]
If 22.8 g of the substance is currently present, what mass A₀ was present 8.00 hours ago?
[tex]A=A_{0}.e^{-k.t}\\22.8g = A_{0}.e^{-0.217h^{-1}\times 8.00h} \\A_{0}=129g[/tex]
