Question

Sally has 100 g each of iodine-131 and radon-222.  

How much of each of these will remain after 32 days?   

What will I-131 decay to and Rn-222 decay to?

Answer 1

a) (i) Let the amount of remaining iodine-131 is m_ir.

   The mass of the iodine m_i=100 g.

   We know the half life of iodine-131 is t_1/2=8 days.

   Let the number of half life is in 32 days is n.

   The number of half life is in 32 days is

                                           

                               

                               

The amount of remaining iodine-131 is

                                     

                              

                              

                              

6.25 g of iodine-131 will remain after 32 days .

(ii)

                

The iodine-131 decay to xenon-131.

b) (i) Let the amount of remaining radon-222 is m_rr.

   The initial amount of radon-222 is m_r=100 g.

   The half-life of radon-222 is t_1/2=3.8 days.

   Let the number of half life is in 32 days is n.

   The number of half life is in 32 days is

      

                                     

The amount of remaining radon-222 is

                                             

                                  

                                  

The amount of remaining radon-222 is 0.2917497972 g or 0.29 g approximately.

(ii)

                  The radon-222 decay to Polonium-218.