Element Z has two natural isotopes: Z-79 (78.918 amu)and Z-81 (80.916 amu).Calculate the atomic mass of element Z given the abundance of Z-81 is 49.31%.

Question

Quizplus · Accepted Answer

To calculate the atomic mass of element Z, we need to weigh the two isotopes by their abundances and add them together:

Atomic mass = (% abundance of Z-79 x mass of Z-79) + (% abundance of Z-81 x mass of Z-81)

We are given the abundance of Z-81, which is 49.31%. Therefore, the abundance of Z-79 must be 100% - 49.31% = 50.69%.

Plugging in the values:

Atomic mass = (50.69% x 78.918 amu) + (49.31% x 80.916 amu)

Atomic mass = 39.998 amu + 39.875 amu

Atomic mass = 79.873 amu

Rounding to the nearest tenth gives us the answer of 79.9 amu, which is choice B.

Element Z Has Two Natural Isotopes: Z-79 (78