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 of these two isotopes?

Answer 1

To find the average mass of an element you add the mass of each isotope multiplied by it's relative abundance.

[(mass of Cu⁶³)x(relative abundance of Cu⁶³)] + [(mas of Cu⁶⁵)x(relative abundance of Cu⁶⁵0)]= average mass of Cu

[(62.9296)x(.6917)] + [(64.9278)x(.3083)] = 63.54amu