Question

lodine-131 is a radioactive isotope with a half-life of 8 days. How many grams of a 50 g sample will be left after 48 days?

Answer 1

Answer:

0.805 or 0.781 depending on the method used.

Explanation:

Data provided

half life ie t1/2= 8days.

No= 50g

t=48days

Nt=?

Method 1

Formula: Nt= No(1/2)^n

where n= number of half lives.

= t/t1/2 = 48/8

=6.

thus Nt= 50(1/2)^6= 0.781

Method 2

Formula: Nt= Noe^-(lambda)t

where lambda= decay constant

= ln2/ t1/2= ln2/ 8 = 0.086.

thus Nt= 50e^-(0.086×48)= 0.805.