Half life worksheet answer key 1. How long does it take a 100.00g sample of As-81 to decay to 6.25g?

The half life of As-81 is 33 seconds;

6.25 g = 100 * (1/2) ^n, where n is the number of half lives

(1/2) ^n = 0.0625

n = 4

Thus, the time taken = 33 * 4 = 132 seconds

Therefore, it takes 132 seconds or 2 mins 12 seconds for it to decay to 6.25 g