Question

Calculate the average atomic mass of an element if an isotope with a mass of 55 amu has a natural abundance of 15% and an isotope with a mass of 56 amu has a percentage abundance of 85%. Please show your work and include appropriate units with your answer.

Answer 1

Average atomic mass = F

1

M

1

+F

2

M

2

+...+F

n

M

n

Where F

1

,F

2

,...F

n

is the fraction representing the natural abundance of the isotope and M is the weight of the isotope.

Avg. At. Mass = (0.85×11)+(0.10×12)+(0.05×13)

= 9.35+1.2+0.65

Therefore, the average atomic mass = 11.2