To determine the mass of Br-79, we need to consider the relative isotopic abundance and the mass of Br-81 as given.
The atomic mass unit (amu) is the unit used to express atomic masses. The atomic mass of an element is an average of the masses of its isotopes, taking into account their relative abundance.
Let's assume the relative isotopic abundance of Br-81 is 100%. Therefore, the mass of Br-81 is given as 80.9163 amu.
Now, let's consider Br-79 as the other isotope. To find its mass, we need to account for the difference in mass between Br-79 and Br-81.
The difference in mass between isotopes is equal to the mass number, which represents the sum of protons and neutrons in the nucleus. Since Br-81 has a mass of 80.9163 amu, we subtract the difference in mass between Br-81 and Br-79 to find the mass of Br-79.
Mass of Br-79 = Mass of Br-81 - Difference in mass
Difference in mass = Mass number of Br-81 - Mass number of Br-79
The mass number of Br-81 is 81, and the mass number of Br-79 is 79.
Difference in mass = 81 - 79 = 2
Mass of Br-79 = 80.9163 amu - 2 amu = 78.9163 amu
Therefore, the mass of Br-79 is approximately 78.9163 amu.