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A drug becomes ineffective after 30% dec...

A drug becomes ineffective after 30% decomposition. The original concentration of a sample was 5 mg/mL , which becomes 4.2 mg/mL during 20 months. Assuming the decomposition of first order, calculate the expiry time of the drug in months.

A

79.4 months

B

36.2 months

C

59.4 months

D

41.0 months

Text Solution

Verified by Experts

`k = (2.303)/(t) log_(10)((a)/(a-x)) = (2.303)/(20)log_(10)((5)/(4.2)) = 0.000862 "month"^(-1)`
.t. may be calculated as : `k = (2.303)/(t)log_(10)""(a)/(a-x)`
`0.00872 = (2.303)/(t) log_(10)""(100)/(70), t = 40.9 ~~41` month
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