sodium-24 has a half life of 15 hours. How much sodium-24 will remain in an 18.0 g sample after 60 hours?

Answer:
Sample remain after 60 hours 1.125 g.
Explanation:
Given data:
Half life of sodium-24 = 15 hours
Total amount of sample = 18 g
Sample remain after 60 hours = ?
Solution:
Number of half lives = T elapsed / half life
Number of half lives = 60 hours/15 hours
Number of half lives = 4
At time zero = 18 g
At first half life = 18 g/2 = 9 g
At second half life = 9 g/ 2= 4.5 g
At third half life = 4.5 g/2 = 2.25 g
At 4th half life = 2.25 g/2 = 1.125 g
Sample remain after 60 hours 1.125 g.