The half-life of sodium-24 is 15 days. A laboratory technician measures out a 72 g sample. Approximately how many grams of sodium-24 would remain after 45 days?

after 45 days 9 g left

Explanation:

Given data:

Half life Na-24 = 15 days

Mass of sample = 72 g

Mass remain after 45 days = ?

Solution:

Number of half lives passed:

Number of half lives = time elapsed / half life

Number of half lives = 45 days / 15 days

Number of half lives = 3

At time zero total amount = 72 g

After first half life = 72 g/ 2= 36 g

At 2nd half life = 36 g/2 = 18 g

At 3rd half life = 18 g/2 = 9 g

Thus after 45 days 9 g left.