Question

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 1

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.

Answer 2

The correct answer should be B) 63.55. That's because the most precise number is 63.546, but you would write 55 because 46 is rounded that way in the equation. The others are a bit higher, while E is a completely different element, Iodine. This isn't the most precise piece of data because in reality there would be a slight differentiation of +- 0,003u