Question

The atomic mass of copper is 63.5u. It exists in the form of two isotopes Cu 63 and Cu 69. Calculate the percentage of each isotope 

Answer 1

copper has two naturally occurring isotopes, copper-63 and copper-65. This means that their respective decimal abundance must add up to give 1.

If you take x to be the decimal abundance of copper-63, you can say that the decimal abundance of copper-65 will be equal to 1−x.

Therefore, 

Copper-63x⋅62.9296u+ copper-65(1−x)⋅64.9278u=63.546u

Solve this equation for x to get

62.9296⋅x−64.9278⋅x=63.546−64.9278

1.9982⋅x=1.3818⇒x=1.38181.9982=0.69152

This means that the percent abundances of the two isotopes will be

● 69.152%→63Cu

● 30.848%→65Cu