There are two naturally occurring isotopes of chlorine. 35 Cl has a mass of 34.9689 u. 37 Cl has a mass of 36.9659 u. Determine the abundance of each isotope.

Abundance for chlorine:

76.9% is 35 Cl and 23.1% is 37 Cl.

Explanation:

the average mass of one mole of chlorine is 35.453g.

Let x be the fraction of the chlorine that is number 35.

1 - x is the fraction that is number 37.

Since they have equal mass number, we equate the two expressions:

34.9689 * x + 36.9659 * (1 - x) = 34.9689 * x + 36.9659 - 36.9659 * x

34.9689 * x + 36.9659 - 36.9659 * x = 35.453

1.997 * x = 1.5359

x = 1.5359 : 1.997

The decimal fraction is approximately 0.769. This means 76.9% is 35 Cl and 23.1% is 37 Cl.