Exercise 8 | Atoms and Molecules

Chlorine (average atomic mass = 35.45 amu) has two stable isotopes. The predominant one is 35Cl with isotopic mass 34.9689 amu and an abundance of 75.77%. What is the most likely other isotope?

We have 75.77% of 35Cl ⇒ % of other isotope: (100-75.77) % = 24.23 % of XCl

Average atomic mass of chlorine = 0.7577 x isotopic mass of 35Cl + 0.2423 x isotopic mass of XCl = 35.45 amu

⇒ isotopic mass of XCl = (35.45 - 0.7577 x isotopic mass of 35Cl) / 0.2423 = 36.95 amu

And, we know that X of XCl ~ isotopic mass of XCl

The second isotope of chlorine is 37Cl