Question

You have a 100-mg sample of I-131. Using Table 7.4 in your text, predict the amount of I-131 that would remain after 32 days. Show your work.

Answer 1

Note Table 7.4 is not provided.

However, the half life of I-131 is well known and it is 8.0 days.

Decay of nuclei obey first order kinetics

for such a nuclei half life = 0.693/k, where k is the decay constant

thus k = 0.693/8. = 0.0864 days^-1

Initially 100 mg sample was there

after 8 days 50 mg sample will be there (one-half life)

after 16 days 25 mg sample will be there (2 half life)

after 24 days 12.5 mg sample will be there (3 half life)

after 32 days 6.25 mg sample will be there (4 half life)

similar ly we can calculate using integrated rate equation. using the value of k

ln X -ln 100 = -kt

where t is time and x is the concnetrstion of unknown

here also we will get x =- 6.25 mg