Chemistry Isotopes Solution: The element bromine has an atomic weight of 79.9 a...

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Solution: 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?

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?

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.


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