## 7B.1

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Edmund Zhi 2B
Posts: 118
Joined: Sat Jul 20, 2019 12:16 am

### 7B.1

A certain beta blocker is eliminated in a first-order process with a rate constant of 7.6 * 10^-3 min^-1 at normal body temperature (37 C). A patient is given 20. mg of the drug. What mass of the drug remains in the body 5.0 h after administration?

How do we use the integrated rate law/rate low to figure this out if we are given only mass, not concentration?

kristi le 2F
Posts: 102
Joined: Thu Jul 11, 2019 12:15 am

### Re: 7B.1

Masses and concentrations are proportional. Through using the equation ln[A]t/[A]0, = -kt, we find that the proportion of [A]t to [A]0 is 1/10. So, 10% of the initial drug concentration remains in the body, which is (0.10)(20 mg) = 2.0 mg.