Question

Naturally occurring iron contains 5.82% 54fe, 91.66 % 56fe, 2.19% 57fe, and 0.33% 58fe. the respective atomic masses are 53.940 amu, 55.935 amu, 56.935 amu, and 57.933 amu. calculate the average atomic mass of iron.

Answer 1

The atomic mass of iron is 55.85 u.

The average atomic mass of Fe 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 % abundance).

Thus,

0.0582 × 53.940 u = 3.139 u

0.9166 × 55.935 u = 51.270 u

0.0219 × 56.935 u = 1.247 u

0.0033 × 57.933 u = 0.191 u

________TOTAL = 55.85 u