Question

Gallium has two natural occuring isotopes: Ga-69 with 68.9256 amu and a natural abundance of 60.11%, and Ga-71 with mass 70.9247 amu and a natural abundance of 39.8%. Calculate the atomic mass of gallium.

Answer 1

To calculate the atomic mass, add each amu multiplied by its relative abundance and divide it all by 100

Ar (Ga) = (68.9256x60.11) + (70.9247x39.8)
/100

= 4,143.12 + 2,822.80 /100

= 69.66