Question

Enter your answer in the provided box. The atomic masses of 63Cu (69.17 percent) and 65Cu (30.83 percent) are 62.94 and 64.93 amu, respectively. Calculate the average atomic mass of copper. The percentages in parentheses denote the relative abundances.

Answer 1

Answer: The average atomic mass of copper is 63.55 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:

$\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i$   .....(1)

• For $_{29}^{63}\textrm{Cu}$ isotope:

Mass of $_{29}^{63}\textrm{Cu}$ isotope = 62.94 amu

Percentage abundance of $_{29}^{63}\textrm{Cu}$ = 69.17 %

Fractional abundance of $_{29}^{63}\textrm{Cu}$ isotope = 0.6917

• For $_{29}^{65}\textrm{Cu}$ isotope:

Mass of $_{29}^{65}\textrm{Cu}$ isotope = 64.93 amu

Percentage abundance of $_{29}^{65}\textrm{Cu}$ = 30.83 %

Fractional abundance of $_{29}^{65}\textrm{Cu}$ isotope = 0.3083

Putting values in equation 1, we get:

$\text{Average atomic mass of Copper}=[(62.94\times 0.6917)+(64.93\times 0.3083)]\\\\\text{Average atomic mass of copper}=63.55amu$

Hence, the average atomic mass of copper is 63.55 amu.