Question

Gallium has an atomic mass of 69.723 amu. The Ga-69 (68.926 amu) is 60.11%. What is the amu of the other isotope?

Answer 1

Answer-

Given,

Atomic mass (Avg. amu) of Gallium = 69.723 amu

Relative abundance of Isotope 1 = 60.11 %

amu of Isotope 1 = 68.926 amu

amu of Isotope 2 (x) = ?

We know that,

Avg amu = (amu of Isotope 1) * (relative abundance of 1) + (amu of Isotope 2) * (relative abundance of 2)--------1

Also,

100% = Relative abundance of 1 + Relative abundance of 2 -----------2

Put the values in 2,

100% = 60.11% + Relative abundance of 2

Relative abundance of 2 = 39.89%

Put values in 1,

Avg amu = (amu of Isotope 1) * (relative abundance of 1) + (amu of Isotope 2) * (relative abundance of 2)

69.723 amu = (68.926 amu * 0.6011) + (amu of Isotope 2 * 0.3989)

amu of Isotope 2 = 70.924 amu

The amu of other isotope is 70.924 amu.