Answer:
180 mg
Explanation:
For a first-order reaction, we can calculate the amount of aspirine (A) at a certain time (t) using the following expression.
[tex]A=A_{0}.e^{-k.t}[/tex]
where,
k: rate constant
A₀: initial amount
If we know the half-life ([tex]t_{1/2}[/tex]) we can calculate the rate constant.
[tex]k=\frac{ln2}{t_{1/2}} =\frac{ln2}{3h} =0.2h^{-1}[/tex]
When t = 4 h and A₀ = 400 mg, A is:
[tex]A=400mg.e^{-0.2h^{-1}\times 4h} =180mg[/tex]
