# Problem: The element bromine has an atomic weight of 79.9 and consists of two stable isotopes bromine-79 and bromine-81. The isotope bromine-79 has a mass of 78.9 amu and a percent natural abundance of 50.5%. The isotope bromine-81 has a percent natural abundance of 49.5%. What is the mass of bromine-81 in amu units?

###### FREE Expert Solution
98% (337 ratings)
###### FREE Expert Solution

We’re being asked to calculate the mass of bromine-81 (Br-81). We can use the following equation:

where atomic mass = average atomic mass of the element and f.a. = fractional abundance of the isotope. To get f.a., we simply need to divide the given percent abundance by 100.

98% (337 ratings)
###### Problem Details

The element bromine has an atomic weight of 79.9 and consists of two stable isotopes bromine-79 and bromine-81.

The isotope bromine-79 has a mass of 78.9 amu and a percent natural abundance of 50.5%.

The isotope bromine-81 has a percent natural abundance of 49.5%.

What is the mass of bromine-81 in amu units?