Homework Help: Chemistry

Posted by David on Tuesday, December 11, 2012 at 11:26pm.

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 - DrBob222, Tuesday, December 11, 2012 at 11:33pm
You need the rate constant which is
k = 0.694/t_{1/2>/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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