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
anor277
Mar 23, 2018

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....

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