Problem: There are two stable isotopes of bromine. Their masses are 78.9183 and 80.9163 amu. If the average atomic mass of bromine is 79.9091 amu, what is the natural abundance of the heavier isotope? The percent abundance of  81Br:

FREE Expert Solution
83% (94 ratings)
FREE Expert Solution

We’re being asked to calculate the percent abundance of bromine-81 (81Br).


We can use the following equation:


Atomic Mass=[mass×f.a.]isotope 1+[mass×f.a.]isotope 2


where: 

atomic mass = average atomic mass of the element 

f.a. = fractional abundance of the isotope

To get f.a., we simply need to divide the given percent abundance by 100.


We’re given the following values:

Average Atomic Mass = 79.9091 amu

Bromine-81: Mass = 80.9163 amu

Bromine-79: Mass = 78.9183 amu


83% (94 ratings)
View Complete Written Solution
Problem Details

There are two stable isotopes of bromine. Their masses are 78.9183 and 80.9163 amu. If the average atomic mass of bromine is 79.9091 amu, what is the natural abundance of the heavier isotope? 

The percent abundance of  81Br:

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Isotopes concept. You can view video lessons to learn Isotopes. Or if you need more Isotopes practice, you can also practice Isotopes practice problems.

What is the difficulty of this problem?

Our tutors rated the difficulty ofThere are two stable isotopes of bromine. Their masses are 7...as medium difficulty.

How long does this problem take to solve?

Our expert Chemistry tutor, Dasha took 8 minutes and 5 seconds to solve this problem. You can follow their steps in the video explanation above.

What professor is this problem relevant for?

Based on our data, we think this problem is relevant for Professor Stevens' class at University of Saskatchewan.