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12 January, 23:43

Sodium only has one naturally occuring isotope, 23 Na, with a relative atomic mass of 22.9898 u. A synthetic, radioactive isotope of sodium, 22 Na, is used in positron emission tomography. 22 Na has a relative atomic mass of 21.9944 u. A 1.8385 g sample of sodium containing a mixture of 23 Na and 22 Na has an apparent "atomic mass" of 22.9573 u. Find the mass of 22 Na contained in this sample?

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  1. 12 January, 23:50
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    Mass of 22-Na contained in the sample = 0.0599 g

    Explanation:

    Mass of the isotope mixture = 1.8385g

    Isotope mixture has apparent mass of 22.9573 u

    23-Na has a relative atomic mass of 22.9898 u

    22-Na has a relative atomic mass of 21.9944 u

    Let the relative abundance of 23-Na be X

    Then the relative abundance of 22-Na would be (1-X)

    21.9944 (1-X) + 22.9898 X = 22.9573

    21.9944 - 21.9944X + 22.9898X = 22.9573

    22.9898X - 21.9944X = 22.9573 - 21.9944

    0.9954X = 0.9639

    X = 0.9674

    Relative abundance of 23-Na = 0.9674

    Relative abundance of 22-Na = 1 - 0.9674 = 0.0326

    Mass of 22-Na in the 1.8385g of sample is

    Relative abundance of 22-Na * Mass of sample = 0.0326 * 1.8385g = 0.0599 g
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