There are two naturally occurring isotopes of bromine. 79Br has a mass of 78.9183 amu. 81Br has a mass of 80.9163 amu. Determine the abundance of each isotope.
Atomic mass of Br = 79.904 Now lets say y% is abundance of 79Br. Then abundance of 81Br = (100 - y) mass due to 79Br = 78.9183 * y/100 = 0.789183y mass due to 81Br = 80.9163 x (100 - y)/100 = 0.809163(100 - y) Therfore 0.789183y+ 0.809163(100 - y) = 79.904 0.789183y + 80.9163 - 0.809163y = 79.904 - 0.01998y= 79.904 - 80.9163 = - 1.0123 y = 1.0123/0.01998 = 50.67% 79Br = 50.67% now 81Br = 100 - 50.67 = 49.33% hope this helps
