What is the weighted average mass of a helium atom ?

Helium contains .0013% of 3 2 He (mass = 3.0160 amu) and 100% of 4 2 He (mass = 4.0026 amu).

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  • Andrew
    Lv 5
    1 decade ago
    Best Answer

    .0013% = .000013

    .000013 x 3.0160 = .000039208 3 2 He

    100% = 1

    1 x 4.0026 = 4.0026 4 2 He

    4.0026 + .000039208 = 4.002639208 amu

    **OR**

    .0013% = .000013

    .000013 x 3.0160 = .000039208 3 2 He

    100% -.0013% = 99.9987%

    99.9987% = .999987

    .999987 x 4.0026 = 4.002548

    4.002548 + .000039208 = 4.002587208 amu

    *** the sig figs are way improper for both it should be 4.0026 but i wrote it with so many for you to decide

  • The atomic weight of Helium is 4.002602 grams per mole.

    Source(s): High School Chemistry book
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