Answer:
Take the weighted average of the individual isotopes.
Explanation:
63
C
u
has
69.2
%
abundance.
65
C
u
has
30.8
%
abundance.
So, the weighted average is
62.93
×
69.2
%
+
64.93
×
30.8
%
=
63.55
amu
.
If we look at the Periodic Table, copper metal (a mixture of isotopes but
63
C
u
and
65
C
u
predominate) has an approximate atomic mass of
63.55
g
⋅
m
o
l
−
1
, so we know we are right.
