Question

Copper, a metal known since ancient times, is used in electrical cables and pennies, among other things. The atomic masses of its two stable isotopes, (69.09 percent) and Cu (30.91 percent), are 62.93 amu and 64.9278 amu, respectively. Calculate the average atomic mass of copper. The relative abundances are given in parentheses.

Answer 1

To find the average atomic mass of copper, multiply the mass of each isotope by its relative abundance, sum these values, and it results in an average mass of approximately 63.5463 amu.

Step-by-step explanation:

To calculate the average atomic mass of copper (Cu), you must use the weights and relative abundances of its stable isotopes. The isotopes in question are Cu-63 and Cu-65. The average atomic mass is found by multiplying the mass of each isotope by its relative abundance (in decimal form) and then summing these values together:

Average atomic mass of Cu = (mass of Cu-63 × relative abundance of Cu-63) + (mass of Cu-65 × relative abundance of Cu-65)

For Cu-63, which has an abundance of 69.09% or 0.6909 in decimal, and a mass of 62.9296 amu, the contribution to average atomic mass is:

Cu-63 Contribution = 62.9296 amu × 0.6909

For Cu-65, which has an abundance of 30.91% or 0.3091 in decimal, and a mass of 64.9278 amu, the contribution is:

Cu-65 Contribution = 64.9278 amu × 0.3091

Adding these two contributions together gives us the average atomic mass:

Calculated atomic mass of Cu = (62.9296 amu × 0.6909) + (64.9278 amu × 0.3091)

= 63.5463 amu

This value is in agreement with the standard atomic weight for copper, which is also 63.546 amu.