Question

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

Answer 1

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%`