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?

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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