Question

An unknown element (called Z) is being researched in the lab. Scientists perform mass spectrophotometry on a sample of the element Z and find the element has four isotopes (mass data below). Use the data in the table to determine the average atomic mass of the unknown element Z.

Isotope Atomic Mass Abundance
Z - 24 23.985 amu 78.90%
Z - 25 24.995 amu 10.00%
Z - 26 25.982 amu 11.00%
Z - 28 27.967 amu 0.10%

Fun question. Best answer 10 points. :) Show your work!

Answer 1

The average atomic mass is = ∑Mi X (Percentage)i / 100

Mi = atomic mass of isotope

Percentage = the percentage of that isotope

so for given

sotope Atomic Mass Abundance

Z - 24 23.985 amu 78.90%

Z - 25 24.995 amu 10.00%

Z - 26 25.982 amu 11.00%

Z - 28 27.967 amu 0.10%

The average atomic mass

= (23.985 X 78.90% + 24.995 X 10.00% + 25.982X 11.00% + 27.967 X 0.10%) / 100

= 24.3097 amu