Bromine has two naturally occurring isotopes, Br-79 and Br-81. The mass of Br-79 is 78.92 amu with a percent abundance of 50.69%. If the atomic mass of bromine is 79.904 amu, calculate the mass and percent abundance of Br-81.
A)80.916 amu and 50.69%
B)78.921 amu and 49.31%
C)79.904 amu and 49.31%
D)80.913 amu and 49.31%
E)80.028 amu and 50.31%

Question

Quizplus · Accepted Answer

The atomic mass of bromine is calculated using the weighted average of its isotopes. Using the given data for Br-79, we can set up the equation: (78.92 * 0.5069) + (mass of Br-81 * 0.4931) = 79.904. Solving for the mass of Br-81 gives approximately 80.913 amu. The percent abundance of Br-81 is 49.31% since the total must equal 100%.

Bromine Has Two Naturally Occurring Isotopes, Br-79 and Br-81