A 1.00 × 10–6 g sample of nobelium-254, has a half-life of 55. What is the percentage of the sample remains after 5 minutes?

Question

A 1.00 × 10^–6 g sample of nobelium-254, has a half-life of 55. What is the percentage of the sample remains after 5 minutes?

Answer 1

Fraction remaining (FR) = 0.5ⁿ where n = number of half lives that have elapsed.

Assuming the half life is given in seconds, i.e. 55 seconds, we can find the number of half lives that have elapsed in 5 minutes.

n = 5 minutes x 60 sec /min = 300 sec x 1 half life / 55 sec = 5.45 half lives elapsed.

FR = 0.5^5.45

FR = 0.0229

Percent remaining = 2.29%