Question

Silver has two naturally isotopes and has an atomic mass of 107.868 amu. One isotope is Ag-109 isotope (108.905 amu) and has a natural abundance of 48.16%. What is the mass in amu of the other isotope

Answer 1

Answer:  106.905

Explanation:  If there are only 2 isotopes, and 1 of them is 48.16%, the second must, by default, be (100 - 48.16%) = 51.84%  The final, averaged, atomic mass is 107.868.  This is made up of each isotope's atomic mass times the percentage of that isotope in the total sample.  The weighted value of the known isotope (109) plus that of the unknown must come to the observed value of 107.868 amu.  (107.868 - 52.45 = 55.42).  Divide that by the % for that isotope (55.42/0.5184) = 106.90 amu for the second isotope.

Atomic Mass  % of Sample Weighted Value

    108.905         48.16%              52.45

          X               51.84%              55.42

                                                     107.87

      X = (55.42/0.5184) = 106.90 amu