Question

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?

Answer 1

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

Explanation:

And so....

`"Atomic mass of Cl"=(34.9689xx75.771%+36.9659xx24.229%)*"amu"`

`-=35.4528*"amu"`

And `35.45*g*mol^-1` 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....