The element copper has an atomic weight of 63.5 and consists of two stable isotopes copper-63 and copper-65. The isotope copper-63 has an atomic mass of 62.9 amu and a percent natural abundance of 69.1%. The isotope copper-65 has a percent natural abundan

The atomic weight of copper is the weighted average of the atomic masses of its isotopes, taking into account their natural abundances. We know the atomic weight of copper is 63.5 and the atomic mass of copper-63 is 62.9 amu with a percent natural abundance of 69.1%. Using this information, we can calculate the atomic mass of copper-65 as follows: atomic weight of copper = (atomic mass of copper-63 x percent natural abundance of copper-63) + (atomic mass of copper-65 x percent natural abundance of copper-65) 63.5 = (62.9 x 0.691) + (atomic mass of copper-65 x 0.309) Solving for the atomic mass of copper-65, we get: atomic mass of copper-65 = (63.5 - (62.9 x 0.691)) / 0.309 = 64.9 amu Therefore, the atomic mass of copper-65 is 64.9 amu.