posted by .

how many half lives have passed if only 0.625g remain of the original 40g?

  • Chemistry -

    (1/2)^n = .625
    n ln(1/2) = ln(.625)
    n = .678

    makes sense, since one full half-life leave 1/2, which is a bit less than .625

  • Chemistry -

    This answer of 0.678 makes no sense to me. By iteration you know that if the sample starts at 40 and ends up at 0.625 it must have gone through six half-lives. Mathematically it is done this way.
    2^n = 40/0.625 = 64
    n*log 2 = log 64
    0.301n = 1.8062
    n = 1.8062/0.301 = 6.0

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemistry

    How many half-lives have passed if 87.5% of a substance has decomposed?
  2. Chemistry

    Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years?
  3. chemistry

    the half-life of polonium-218 is 3.0 minutes. what percentage of the original sample remains after 4 half-lives?
  4. Chemistry

    K-42 has a half-life of 12.4 hours. If you begin with 250g of K-42, determine how much you will have left after 4 half-lives. How long does 4 half-lives take?
  5. chemistry

    how many half-lives of radon-222 have passed in 11.46 days?
  6. science

    how many half-lives have passed if only 1/16 of the original amount of the element remains?
  7. chemistry

    Find the number of disintegrations per minute emitted by 1.1 mol of 232-Th in 1 min. The half-life of 232-Th is 1.4 x 1010 year I was able to do this with the following technique: 1.1 x 6.022 x10^23 =6.62x10^23 1.4x10^10=7.358x10^15 …
  8. chemistry

    what fraction of an original sample of a radioactive isotope remains after three half-lives have passed?
  9. Chemistry

    If a 100.0 gram sample of a radioactive isotope goes through three half-lives, how much of the original radioactive isotope will remain?
  10. Chemistry

    A substance undergoes a first-order decomposition. After 40.0 min at 500 degrees C, only 12.5% of the original sample remains. What is the half-life of the decomposition?

More Similar Questions