In 5.49 seconds, 1.80 g of argon-35 decay to leave only 0.225 g. What is the half-life of argon-35?

Half life = 1.83 sec

Explanation:

Given data:

Total amount of Ar-35 = 1.80 g

Amount left after 5.49 sec = 0.225 g

Half life of Ar-35 = ?

Solution:

At time zero = 1.80 g

At first half life = 1.80 g/2 = 0.9 g

At 2nd half life = 0.9 g/2 = 0.45 g

At 3rd half life = 0.45 g/2 = 0.225 g

Half life:

Half life = Time elapsed / number of half lives

Half life = 5.49 sec / 3

Half life = 1.83 sec