Given relative abundance of the following naturally occuring isotopes of oxygen, calculate the average atomic mass: O-16: 99.76% , O-17: 0.037% , O-18: 0.204%

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justaguide eNotes educator| Certified Educator

The atomic mass of oxygen is the average mass of oxygen weighted with the abundance. For the isotope with mass 16, the concentration is 99.76% which is the weight to be used. For the isotope with mass 17, the concentration is 0.037% which is the weight. For the isotope with mass 18, the concentration is 0.204% which is the weight to be used.

The weighted average mass is: 16*0.9976 + 17*0.00037 + 18*0.00204 = 16.00461

The average atomic mass of oxygen is 16.00461