Question

If 75.0 of the isotopes of an element have a mass of 39.0 and 25.0% of the isotopes have a mass of 36.0 amu, what is the atomic mass of the element?

Answer 1

Atomic mass of element = 38.25 amu

Step-by-step explanation:

Let X-39 abundance = 75% and X-36 abundance = 25%

Atomic Mass of element = ∑ wt average contributions of each isotope ...

Wt Avg Contribution = fractional abundance x isotopic mass.

Isotope Isotopic Mass (amu) Fractional Abundance Wt Avg Contbn

X-39 39.00 0.75 29.25 amu

X-36 36.00 0.25 9.00 amu

∑ Wt Avg Contributions = 29.25 amu + 9.00 amu = 38.25 amu

=> Atomic mass of element = 38.25 amu