Question

Copper atoms exhibit two masses: 62.929 amu for 67.93% and 64.927 amu for the remaining. What is the average atomic mass of copper?

a) 62.929 amu
b) 63.186 amu
c) 64.927 amu
d) 65.456 amu

Answer 1

The average atomic mass of copper is found by multiplying each isotope's mass by its relative abundance and summing the results. The calculation (62.929 amu * 0.6793) + (64.927 amu * 0.3207) yields an average atomic mass of 63.553 amu, making option b) 63.186 amu the nearest correct answer.

Step-by-step explanation:

To calculate the average atomic mass of copper, we must take into account the masses of its stable isotopes and their relative abundances. The mass of copper-63 is 62.929 amu and its abundance is 67.93%. The mass of copper-65 is 64.927 amu with the remaining abundance of 32.07% (100% - 67.93%).

We use these values in the following weighted average formula:

1. Multiply each isotope's mass by its abundance (in decimal form).
2. Add the results together.
3. The sum is the average atomic mass of the element.

Calculation:

(62.929 amu * 0.6793) + (64.927 amu * 0.3207) = 42.738 amu + 20.815 amu = 63.553 amu

Hence, the correct answer is b) 63.186 amu, which is the closest option provided to the calculated average of 63.553 amu.