Question

Copper has two naturally occurring isotopes. Cu-63 has a mass of 62.939 amu and a relative abundance of 69.17%.

Use the atomic mass of copper to determine the mass of the other copper isotope.

Express your answer using four significant figures.

Answer 1

mass of other isotope = 64.91 amu

Explanation

Abundance of Cu-63 = 69.17 %

Abundance of Cu-65 = 100 % - (Abundance of Cu-63)

Abundance of Cu-65 = 100 % - 69.17 %

Abundance of Cu-65 = 30.83 %

Atomic mass of copper = [(Abundance of Cu-63) * (atomic mass Cu-63) + (Abundance of Cu-65) * (atomic mass Cu-65)] / 100

63.546 amu = [(69.17) * (62.939 am) + (30.83) * (atomic mass Cu-65)] / 100

6354.6 amu = [4353.49 amu + (30.83) * (atomic mass Cu-65)]

(30.83) * (atomic mass Cu-65) = 6354.6 amu - 4353.49 amu

(30.83) * (atomic mass Cu-65) = 2001.1 amu

atomic mass Cu-65 = (2001.1 amu) / 30.83

atomic mass Cu-65 = 64.91 amu