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March 29, 2017

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Assume that the element 107Uns is synthesized and that the sample contains 39.8% 270Uns (269.4 amu), 35.2% 271Uns (270.3 amu) and 25.0% 272Uns (271.2 amu). What is the value of the atomic weight?

A. 270.
B. 269.3
C. 270.4
D. 271

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So this is what I did, but for some reason, it continues to not turn out. SO i am thinking is it significant figures reason?

here is what i have, please tell me what i am doing wrong and what the answer is?

this is what i did:

(39.8/100) (269.4 amu) + (35.2/100) (270.3 amu) + (25.0/100)(271.2 amu)

And I got 270.1668 amu

But it isn't one of the choices. So I was thinking is it because of significant figures or miscalculation? OR what would the answer be?

  • Chemistry - ,

    It can't be B and the mass is less than the mass of any of the isotopes.

    The % values are to three sig figs so might expect the answer to be to 3 sig figs. The only one that fits is A.
    If you round each step to 3 sig figs and then add you get 269.9 or 270 to 3 sig figs.

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