Question

1-Nitrogen occurs in the nature in the form of two isotopes with atomic mass 14 and 15 respectively. if

Average atomic mass of nitrogen is 14.0067,what is the percentage abundance of two isotopes?

Answer 1

Dear student!
Average atomic mass of two isotopes is calculated as:

average atomic mass = (mass of one isotope A x %age abundance) + (mass of isotope B x %age abundance)

Hence, Let %age of N-14 is X % then percentage of N-15 will be (100-X) % , so putting the values,

14.00067 = 14 x X/100 + 15 (100-X)/100

or, (14X + 1500- 15X)/100 = 14.0067

Or, X = 1500 - 1400.67 = 99.33 %

Hence %age of N-14 isotope is 99.33 while that of N-15 isotope is 0.67