Question

1. Native copper is a mixture of two isotopes. Copper-63 contributes 69.17% of the atoms of copper and copper-65 the remaining 30.83%. What is the average atomic mass?​

Answer 1

Answer: 63.6166 amu (atomic mass units)

Explanation: When an element X is written in the form of X-N, N will the atomic mass of that element. So we have copper with a mass of 63 and 65. We are given percentages of each one. 69.17/100 of the copper atoms will be of weight 63 while 30.83/100 will be of weight 65. Keep in mind that amu does not actually mean weight but I'm just using it as a tool to help explain the general concept. Assume you have 100 copper atoms, and you need to find the average atomic mass for them, if you do this you will solve the problem. Due to the fractions, 69.17 of them will be 63 amu and the rest will be 65. So do 69.17*63+65*30.83 and divide by one hundred. By doing this you will get 63.6166. If my answer doesn't make sense, search up how to calculate weighted averages

Hope this helps