Question

32P is a radioactive isotope with a half-life of 14.3 days. If you currently have 30.9 g of 32P, how much 32P was present 4.00 days ago?

in grams

Answer 1

K    =   0.693/t1/2

t1/2   = 14.3days

k      = 0.693/14.3   = 0.0485days^-1

t = 4days

[A0]   = 30.9g

k     = 2.303/t log[A0]/[A]

0.0485   = 2.303/4 log30.9/[A]

log30.9/[A]   = 0.0485*4/2.303

log30.9/[A]     = 0.084237

30.9/[A]           = 10^0.084237

30.9/[A]            = 1.214

[A]                   = 30.9/1.214

[A]                    = 25.45g >>>>answer