Copper exists in nature as two isotopes. the atomic masses and relative abundance of these isotopes is given in the table. what is the average atomic mass of copper?
a) 62.93 amu
b) 63.55 amu
c) 63.935 amu
d) 64.94 amu
e) 127.87 amu

Answer : Option B) 63.55 amu

Explanation : To find the average atomic weight of the two isotopes of copper that exist in nature we can use the below formula;

Average atomic mass = ∑ (isotope(s) x abundance)

Therefore, we have the given values of atomic masses of two copper isotopes are 62.93 u and 64.93 u, respectively. They have natural abundance as 0.692 and 0.368, respectively,

On substituting the above values, we get,

Average atomic mass = (62.93 x 0.692) isotope 1 of Cu + (64.93 x 0.308) isotope 2 of Cu

Average atomic mass = 43.54 + 19.99 = 63.538 ~ 63.55

Therefore, the average atomic mass of Cu will be 63.55 amu.