Chlorine has two isotopes. Chlorine-35 has an actual mass of 34.9689 u and chlorine-37 has a mass of 36.9659 u. In any sample of chlorine atoms, 75.771% will be chlorine-35 and 24.229% will be chlorine 37. What is the average atomic mass of chlorine?

1 Answer
Mar 23, 2018

Take the weighted average of the isotopic masses....

Explanation:

And so....

Atomic mass of Cl=(34.9689×75.771%+36.9659×24.229%)amu

35.4528amu

And 35.45gmol1 is the mass we generally take for chlorine...as the weighted average of 35Cl and 37Cl isotopes. Because the less massive isotope is MORE abundant, the average atomic mass is closer to the mass of this of this isotope....