Bromine has two naturally occurring isotopes (Br-79 and Br-81) and an atomic mass of 79.904 amu.
(a) If the natural abundance of Br-79 is 50.69%, what is the natural abundance of Br-81?
(b) If the mass of Br-81 is 80.9163 amu, what is the mass of Br-79?
Here, we are going to calculate the natural abundance of Br-81 and the mass of Br-79.
Atomic mass can be defined as the average mass of the isotopes of that element. If an element has no isotopes, then the mass of its atom would be the same as the sum of protons and neutrons in it. But if an element occurs in isotopic forms, then we have to know the percentage of each isotopic form and then the average mass is calculated.
The general formula for calculating the atomic mass of an element having n number of isotopes is given below:
Atomic mass = (fraction of isotope n) x (mass of isotope n) ----(1)
Step 2:Given, natural abundance of Br-79 = 50.69 %
Therefore, natural abundance of Br-81 = 100 - 50.69 = 49.31 %