Question

Naturally occurring copper has an atomic weight of 63.55 amu. Its principal isotopes are 63Cu and 65Cu. What is the abundance (in atomic percent) of each isotope? g

Answer 1

Answer: Percentage abundance of Cu-63 isotope = 72.5%

Percentage abundance of Cu-65 isotope = 27.5 %

Explanation:

Average atomic mass 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:

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

We are given:

Two isotopes of copper, which are Cu-63 and Cu-65

Average atomic mass of silicon = 63.55 amu

$63.55={(63\times x)+ (65\times (1-x))}$

$x=0.725$

$(1-x)=(1-0.725)=0.275$

Percentage abundance of Cu-63 isotope = 72.5%

Percentage abundance of Cu-65 isotope = 27.5 %