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18 May, 11:54

Oxygen has three naturally occurring isotopes in the following proportions oxygen 16,99.762% (15.994 91 u); oxygen 17, 0.038000% (16.999 13 u); oxygen 18, 0.20000% (17.999 16 u). What is the average atomic mass of oxygen?

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Answers (2)
  1. 18 May, 13:19
    0
    The average atomic mass is 15.9993

    Why?

    Take the percentage and times it by the amu and then add all the new numbers together to get the average atomic mass:

    (0.99762 x 15.99491) + (0.00038 x 16.99913) + (0.002 x 17.9916) = 15.9993
  2. 18 May, 14:24
    0
    Answer

    15.999 u

    Explanation:

    The atomic mass of O is the weighted average of the atomic masses of its isotopes.

    We multiply the atomic mass of each isotope by a number representing its relative importance (i. e., its percent of the total).

    Set up a table for easy calculation

    0.997 62 * 15.994 91 u = 15.956 8 u

    0.000 38 * 16.999 13 u = 0.006 46 u

    0.002 00 * 17.999 16 u = 0.036 00 u

    TOTAL = 15.999 u
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