Naturally occurring element X exists in three isotopic forms: X-28 (27.979 u,90.64% abundance),X-29 (28.976 u,4.00% abundance),and X-30 (29.974 u,5.36% abundance).Calculate the atomic weight of X.
A) 29.64 u
B) 28.13 u
C) 28.99 u
D) 29.83 u
E) 27.15 u

Question

Quizplus · Accepted Answer

The atomic weight of an element is calculated by multiplying the mass of each isotope by its natural abundance (expressed as a fraction), then summing these products. For element X:- For X-28: $27.979 \, \text{u} \times 0.9064 = 25.351 \, \text{u}$- For X-29: $28.976 \, \text{u} \times 0.04 = 1.159 \, \text{u}$- For X-30: $29.974 \, \text{u} \times 0.0536 = 1.606 \, \text{u}$Adding these together gives the atomic weight of X: $25.351 + 1.159 + 1.606 = 28.116 \, \text{u}$, which rounds to $28.13 \, \text{u}$.

Naturally Occurring Element X Exists in Three Isotopic Forms: X-28