Question

Copper is made of two isotopes. Copper-63 is 69.17% abundant and it has a mass of 62.9296 amu. Copper-65 is 30.83% abundant and it has a mass of 64.9278 amu. What is the weighted average mass of these two isotopes?

Answer 1

Answer: The average atomic mass of copper is 65.5456 amu.

Explanation: Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

.....(1)

For isotope:

Mass of isotope = 62.9296 amu

Percentage abundance of isotope = 69.17 %

Fractional abundance of isotope = 0.6917

For isotope:

Mass of isotope = 64.9278 amu

Percentage abundance of isotope = 30.83%

Fractional abundance of isotope = 0.3083

Putting values in equation 1, we get:

Thus, the average atomic mass of copper is 65.5456 amu.