Question

Iodine-131 decays with a half-life of 8.02

Answer 1

Radioactive material undergoes 1st order decay kinetics.

For 1st order decay, half life = 0.693/k

where k = rate constant

k = 0.693/half life = 0.693/8.02 = 0.0864 day-1

Now, for 1st order reaction,
k = $\frac{2.303}{t} X log \frac{initial.conc}{final.conc}$

Given: t = 6.01d, initial conc. = 5mg

∴0.0864 = $\frac{2.303}{6.01} X log \frac{5}{final.conc}$
∴ final conc. = 2.975 mg