How long will it take for 25% of the C-14 atoms in a sample of C-14 to decay? The half-life for the radioactive decay of C-14 is 5730 years.

If a sample of C-14 initially contains 1.1 mmol of C-14 , how many millimoles will be left after 2275 years?

3 answers

Both problems are similar. Use this first equation to evaluate k.
k = 0.693/t1/2
Then substitute k into this equation.
ln(No/N) = kt
To make thing easy I would assume we start with 100 atoms so No = 100. If 25% of the atoms decay, that will leave 75 atoms remaining; therefore, N = 75. You know k from the first equation, you can solve for time.
Second problem is done the same way but you solve for N.
2000 Years
the answer is 2400 years, based on the equation ln(100/75)/(1.2xE^-4). And the 1.2xE^-4 is the k
Similar Questions
    1. answers icon 3 answers
    1. answers icon 5 answers
  1. A sample of C3H8 has 2.64 x 10^24 atoms.How many carbon atoms does the sample contain? What is the total mass of the sample? I
    1. answers icon 0 answers
  2. A sample of propane(c3h8)has 3.84x10^24 H atoms.a) how many carbon atoms does the sample contain? b) what is the total mass of
    1. answers icon 5 answers
more similar questions