Final answer:
To find the atomic mass of an element with two isotopes, multiply the mass of each isotope by its respective abundance, expressed as a decimal, then sum the results. The atomic mass of this element, rounded to two decimal places, is 69.74 amu.
Step-by-step explanation:
The atomic mass of the element with its two naturally occurring isotopes is calculated by multiplying the mass of each isotope with its relative abundance (expressed as a fraction), and then adding the products together. The formula for this calculation is:
Atomic mass = (fractional abundance of isotope 1 × mass of isotope 1) + (fractional abundance of isotope 2 × mass of isotope 2)
In this case:
- Atomic mass = (0.6011 × 68.928 amu) + (0.3989 × 70.925 amu)
- Atomic mass = (41.4299768 amu) + (28.306575 amu)
- Atomic mass = 69.7365518 amu
Therefore, the average atomic mass of the element is approximately 69.74 amu.