Question

If you have 500g of krypton-85, how much remains, and how much time passes after 4 half-lives pass (krypton's half-life is 10.8 years).

Answer 1

After 4 half-lives of krypton-85, which is 43.2 years, 31.25g of the original 500g would remain.

Step-by-step explanation:

If you have 500g of krypton-85, after 4 half-lives have passed, you'll want to calculate how much of the substance remains. Krypton's half-life is given as 10.8 years. To determine the remaining amount, you would perform the following calculation:

• After one half-life (10.8 years), 50% of the original amount would remain, so you'd have 250g.
• After two half-lives (21.6 years), you'd have half of that amount, so 125g.
• After three half-lives (32.4 years), you'd have half of 125g, which is 62.5g.
• Finally, after four half-lives (43.2 years), you'd have half of 62.5g, which is 31.25g remaining.

Therefore, after 4 half-lives, or 43.2 years, you would have 31.25g of krypton-85 remaining from the original 500g.