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Chemistry LibreTexts

General F005: Atomic Mass

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  • All atomic masses in this quiz are based on the standard atomic mass scale, where pure carbon-12 is defined as having an atomic mass of exactly 12 mass units.

    The following questions are multiple choice; clearly circle the answer which you think is the most appropriate. These questions are for self-testing only, and are not suitable for assignments or exams.

    1. On Earth, the element boron is a mixture of two isotopes, boron-10 and boron-11. Boron-10 has an atomic mass of 10.013 and makes up 19.9% of the total; the remaining 80.1% is boron-11, with an atomic mass of 11.009. What is the standard atomic weight for terrestrial boron?

    A 10.5
    B 10.8
    C 50.5
    D 63.98

    2. A mass spectrometer shows that a sample of terrestrial copper contains two isotopes: 63 Cu(69.15%, atomic mass 62.9296) and 65Cu (30.85%, atomic mass 64.9278). What is the atomic weight for this sample of copper?

    A 301.46
    B 70
    C 63.55
    D 65

    3. A sample of helium from Jupiter contains 0.022% 3He (atomic mass 3.0160) and 99.978% 4He (atomic mass 4.0026). Calculate the atomic weight for this sample of helium.

    A 3.5066
    B 4.0024
    C 4.0026
    D 3.0106


    1. B

    2. C

    3. B