Question

Naturally occurring iron contains:

5.82% 54Fe (atomic mass = 53.940 amu)
91.66 % 56Fe (atomic mass = 55.935 amu)
2.19% 57Fe (atomic mass = 56.935 amu)
0.33% 58Fe (atomic mass = 57.933 amu)
Calculate the average atomic mass of iron.

Answer 1

The average atomic mass of iron is the sum of the products of the percentage abundance and masses of the isotopes. That is,
average atomic mass = 0.0582 x 53.940 amu + 0.9166 x 55.935 amu + 0.0219 x 56.935 amu + 0.0033 x 57.933 amu = 55.847 amu
Thus, the average atomic mass of iron is approximately 55.847 amu.