A sample of copper (Cu) contains 69.17% Cu-63. The remaining copper atoms are Cu-65. What is the average atomic mass of copper?

1 Answer
anor277
Feb 4, 2017

#"Average atomic mass = 63.62 amu"#

Explanation:

#"Average atomic mass"# is the weighted average of the individual isotopes.

And thus the weighted average #=#

#(0.6917xx63+0.3083xx65)*"amu"# #=# #"?? amu"#.

Note that we have not accounted for the less massive copper isotopes that would decrease this mass to the accepted value of #63.55# #"amu"#.

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