Question

Enter your answer in the provided box. many drugs decompose in blood by a first-order process. two tablets of aspirin supply 0.60 g of the active compound. after 30 min, this compound reaches a maximum concentration of 2 mg/100 ml of blood. if the half-life for its breakdown is 90 min, what is its concentration (in mg/100 ml) 2.5 h after it reaches its maximum concentration?

Answer 1

First, we should get K, and we can get it from this equation:
K= ㏑(2)/t1/2
when we have t1/2 (the half-life time )= 90 min so by substitution:
K= ㏑(2) / 90 min
  =0.0077
Then we can get C ( the amount remains at time t) from this equation:
C= Ae^(-Kt)
 we have A(amount at t=zero) = 2 g / mL
& K = 0.0077 & t = 2.5 h, convert it to min 2.5*60 = 150 m
by substitution:
C= 2* e^(-0.0077*150)
  = 2 * 0.315 = 0.63 g/mL