Potassium has a half-life of 12 hours. What fraction of a 100g sample is left after 48 hours

After 48 hours amount left = 6.25 g

Explanation:

Given data:

Half life of potassium = 12 hours

Total mass = 100 g

Mass left after 48 hours = ?

Solution:

Number of half lives passed:

Number of half lives = Time elapsed / half life

Number of half lives = 48 hours/ 12 hours

Number of half lives = 4

At time zero = 100 g

At first half life = 100 g/ 2 = 50 g

At 2nd half life = 50 g/2 = 25 g

At 3rd half life = 25 g/2 = 12.5g

At 4th half life = 12.5 g/2 = 6.25 g