Question

Element X has two known naturally occurring isotopes. The mass and relative abundance of each isotope are shown below.

Isotope 1:
Relative Abundance: 50.57%
Mass (amu): 78
Isotope 2:
Relative Abundance: 49.43%
Mass (amu): 81
What is the average atomic mass of Element X to the nearest hundredth of an atomic mass unit?
A. 79.04 amu
B. 79.48 amu
C. 79.48 amu
D. 80.48 amu

Answer 1

The average atomic mass of Element X is calculated by multiplying each isotope's mass by its relative abundance and adding the results together, which yields 79.48 amu.

Step-by-step explanation:

To calculate the average atomic mass of an element with multiple isotopes, we multiply the mass of each isotope by its relative abundance and sum the results. Here is the calculation for Element X:

• (0.5057)(78 amu) + (0.4943)(81 amu)
• (39.4446 amu) + (40.0383 amu)
• 79.4829 amu

Rounding to the nearest hundredth of an atomic mass unit gives us 79.48 amu as the average atomic mass of Element X.