A 200.0-ng sample of sodium-24 was stored in a lead-lined cabinet for 45 hours.The half-life of sodium-24 is 15 hours.How much sodium-24 remains?

Question

Quizplus · Accepted Answer

After 45 hours, which is three half-lives of sodium-24 (15 hours x 3 = 45 hours), the amount of sodium-24 would have halved three times. Starting with 200 ng, after the first half-life, it would be 100 ng; after the second, 50 ng; and after the third, 25 ng.

A 2000-Ng Sample of Sodium-24 Was Stored in a Lead-Lined Cabinet