Chemistry questions

Question

Carbon-14 has a half-life of 5715 years. If a sample of carbon-14 has and original mass of 12 g, what will be the amount remaining at the end of 10,788 years? Write out your equations and type out your calculations to show your work to the best of your ability. Answers should have the correct number of significant figures and unit.

Answer 1

For a first order decay, we have...

FR = 0.5ⁿ

FR = fraction remaining = ?

n = number of half lives elapsed = 10,788/5715 = 1.8877

FR = 0.5^1.8877 = 0.2702

Amount remaining in grams = 0.2702 x 12 g = 3.24 g = 3.2 g (2 sig. figs.)

Answer 2

Half life equation

A(t) = C (0.5)^t/H

A(t) - amount remaining after time t

H = half life (same units as t)

C = amount at start

So here H = 5715, C = 12, t = 10788. You can find A(t).

Units will be in grams.

5715 has 4 sfs

10788 has 5 sfs

12 has 2 sfs

minimum of 2, 4 and 5 is 2. So you should give your answer to 2 sfs.