Skill 3. Calculating the atomic mass of an element from isotopic composition
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Problem: Silver (Ag; Z =47) has only two isotopes that occur naturally, 107Ag and 109Ag. Given the mass spectrometric data, calculate the atomic mass of silver:
ISOTOPE MASS (amu) ABUNDANCE (%) 107Ag 106.90509 51.84
109Ag 108.90476 48.16
Solution: Finding atomic mass contribution of each isotope: Portion of atomic mass = isotopic mass x fractional abundance For 107Ag: = 106.90509 amu x 0.5184 = 55.42 amu For 109Ag: = 108.90476 amu x 0.4816 = 52.45 amu
Finding the atomic mass of silver: Atomic mass of Ag = 55.42 amu + 52.45 amu = 107.87 amu
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