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.
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?
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