5. The element copper has naturally occurring isotopes with mass numbers of 63

and 65. The relative abundance and atomic masses are 69.2% and 30.8%

respectively. Calculate the average atomic mass of copper.

Average atomic mass = 63.62 amu.

Explanation:

Abundance of Co⁶³ = 69.2%

Abundance of Co⁶⁵ = 30.8%

Atomic mass of Co⁶³ = 63 amu

Atomic mass of Co⁶⁵ = 65 amu

Average atomic mass = ?

Solution:

Average atomic mass = (abundance of 1st isotope * its atomic mass) + (abundance of 2nd isotope * its atomic mass) / 100

Average atomic mass = (63*69.2) + (65*30.8) / 100

Average atomic mass = 4359.6 + 2002 / 100

Average atomic mass = 6361.6 / 100

Average atomic mass = 63.62 amu.