posted by John

How many half-lives have passed if 87.5% of a substance has decomposed? How many if 99.999% has decomposed?

For 87.5% decomposition 1/8 is left.
(1/8) = (1/2)^3
Three half lives is the answer

Fot 99.999% decomposition, 10^-5 is left.
Solve 10^-5 = (1/2)^n for the number of half-lives, n. Take the log of each side of the equatiuon for a quick solution.

Respond to this Question

First Name

Your Answer

Similar Questions

  1. half-life

    1. The half-life of a first-order reaction is 9.89 minutes. How many minutes will have elapsed after 27 half-lives?
  2. MATH 156

    Write the numbers in order of increasing size. "can anyone please help me I think the answer is A am I correct?
  3. Science Half Lives

    I am confused about how to claculate half lives. Can you explain. ( How much of a 400 gm sample od gold is left after 10.8 days if the half life is 2.7)
  4. science

    how many half-lives have passed if 87.5% of a substance has decomposed?
  5. 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?
  6. science

    Using absolute dating,a fossil is dated to be 3 million years old and decomposed 1 half-life. If it takes the same fossil 12 million years to decompose to 4 half-lives,how old will the fossil be when it is measured to be at 3half-lives?
  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

    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?
  10. math

    The half life of the radio active substance is the time require the half the substance to decay. the mount A ( in grams) of 100 gram sample of a radio active substance remaining after t half lives by A equals to 100 (0.5) t. suppose …

More Similar Questions