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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?
please help

  • Chemistry -

    There is a shorter way, I think, but this is what I would do.
    k = 0.693/t1/2
    Substitute k into the equation below.
    ln(No/N) = kt
    No = 250
    N = unknown
    k from above.
    t = time = 4*12.4 = ??

    The short way is (n = number of half lives)
    1/2^n = fraction left
    1/2^4 = ?? and ?? x 250 = xx.
    You should get the same answer either way.

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