Question

An element has three naturally occurring isotopes. Use the information below to calculate the weighted average atomic mass of the element, showing both the setup and the final answer for the calculation.

Isotope
Atomic Mass
Percent Abundance
I
39.96 u
99.59%
II
37.96 u
0.065%
III
35.97 u
0.336%

Answer 1

To find average atomic mass you multiple each mass by the percent abundance, and then add them. (39.96)(.9959) + (37.96)(.00065) + (35.97)(.00336) = 39.796 + .02467 + .120859
= 39.94