Question

Copper has two naturally occurring isotopes and an atomic mass of 63.546 amu. cu-63 has a mass of 62.940 amu and an abundance of 69.17%. what is the identity and percent abundance of copper's other isotope? (type your answer for identity using the format cl-35 for chlorine-35.)

Answer 1

The average atomic mass of copper = 63.546 amu

Copper has two natural isotopes.

The % abundance of the first isotope Cu-63 is 69.17 %

Mass of the isotope Cu-63 = 62.940 amu

The percentage abundance of other isotope will be 100 - 69.17 % = 30.83 %

Let the atomic mass of other isotope be x amu

Average atomic mass is the weighted average of the atomic masses of all isotopes of an element.

$63.546 amu = 62.940 amu (0.6917) + x (0.3083)$

x = 64.90 amu

The atomic mass of other isotope of copper is 64.90 amu

Therefore, the isotope will be Cu-65