Question

Naturally occurring element x exists in three isotopic forms: x-28 (27.977 amu, 92.23% abundance), x-29 (28.976 amu, 4.67% abundance), and x-30 (29.974 amu, 3.10% abundance). calculate the atomic weight of x.

Answer 1

To solve for the weighted average atomic weight of X, all we have to do is to calculate for the contribution of each isotope. The contribution of each isotope on the atomic weight of x is calculated by multiplying their respective atomic weights with the abundance, therefore:

X – 28 = 27.977 amu * (92.23 / 100)

X – 28 = 25.803 amu

 

X – 29 = 28.976 amu * (4.67 / 100)

X – 29 = 1.353 amu

 

X – 30 = 29.974 amu * (3.10 / 100)

X – 30 = 0.929 amu

 

Hence:

X = X – 28 + X – 29 + X – 30

X = 25.803 amu + 1.353 amu + 0.929 amu

X = 28.085 amu