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If the half-life of uranium-235 is 7.04 (times) 10 (to the eight power) 8 y and 12.5 g of uranium-235 remain after 2.82 (times) 10 (to the ninth power) y, how much of the radioactive isotope was in the original sample?

  • Chemistry -

    You need the rate constant which is
    k = 0.694/t1/2>/sub>
    Substitute k into the equation below.
    ln(No/N) = kt.
    No is what you wnat to know.
    N = 12.5g from the problem.
    k from above.
    t = 2.82E9 yr.
    Substitute and solve for N.

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