Question

Naturally occurring cobalt consists of only one isotope, 59Co, whose relative atomic mass is 58.9332. A synthetic radioactive isotope of cobalt, 60Co, relative atomic mass 59.9338, is used in radiation therapy for cancer. A 1.8276g sample of cobalt has an apparent "atomic mass" of 58.9901.Find the mass of 60Co in this sample.

Answer 1

let x = fractional abundance of 59Co.
and 1-x = fractional abundance of 60Co.
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x(58.9332) + (1-x)(59.9338) = 58.9901
Solve for x and 1-x to obtain fractional abundances for Co59 and Co60.
Then 1.8276 g x fractional abundance Co60 = mass Co60 in the sample.

Answer 2

it is .104 g correct?

Answer 3

I agree with what you have but if your prof is picky about significant figures s/he will tell you that you need another place in your answer. I believe you are allowed four s.f. so I would write that as 0.103928 which I would round to 0.1039 g.