An element found in another galaxy exists as two isotopes. If 80.0 percent of the atoms have an atomic mass of 80.00 amu and the other 20.0 percent have an atomic mass of 82.00 amu, what is the atomic mass of the element?
A)81.0 amu
B)64.0 amu
C)80.4 amu
D)16.4 amu
E)81.6 amu

Question

Quizplus · Accepted Answer

To find the atomic mass of the element, we need to take a weighted average of the two isotopes based on their abundance (percentage).

Atomic mass = (abundance of isotope A x atomic mass of isotope A) + (abundance of isotope B x atomic mass of isotope B)

Plugging in the values, we get:

Atomic mass = (0.80 x 80.00 amu) + (0.20 x 82.00 amu)
Atomic mass = 64.00 amu + 16.40 amu
Atomic mass = 80.40 amu

Therefore, the atomic mass of the element is 80.4 amu.

An Element Found in Another Galaxy Exists as Two Isotopes