Question

Chlorine has two principle isotope Cl37 having an isotopic mass of 36.96590259 and Cl35 with and isotropic 34.9688268. Calculate the percentage of abundance of the chlorine isotopes, if the average mass of a chlorine atom is 35.5

Answer 1

Let's assume the total number of chlorine atoms is 100 in which, there are 'y' Cl₃₇ atoms and thus (100 - y) Cl₃₅ atoms.

As given, the average mass of a Cl atom is 35.5;

Therefore,

35.5 x 100 = (36.96590259.y) + (100 - y).(34.9688268)

or, 3550 = y(36.96590259 - 34.9688268) + 3496.88268

or, 1.99707579.y = 53.11732

or, y = 26.598

thus, (100-y) = 73.408

Thus, in general there is 26.598% Cl₃₇ and 73.408% Cl₃₅ atoms.