How would you find the percent abundance of 2 isotopes of an element, given the atomic weight and mass number of each isotope?

1 Answer
Dr. Hayek
Nov 11, 2015

See explanation.

Explanation:

The average atomic mass of elements is calculated by:

#Mass_(avrg.)=sum("isotope mass")*("percent abundance")#

For example, suppose we want to find the percent abundance of chlorine isotopes #""^35Cl# and #""^37Cl# given that the average atomic mass of chlorine is #35.45 "a.m.u.#.

Assume that the percent abundance of #""^35Cl# is #x#, therefore, the percent abundance of #""^37Cl# is #1-x#.

Thus, #35.45=(35xxx)+(37xx(1-x)) => 35.45 = 37 -2x#.

Solve for #x#, #x=0.775#

Therefore, the percent abundance of #""^35Cl# is #77.5%# and the percent abundance of #""^37Cl# is #22.5%#

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