Calculating % Abundance of Br-79 & Br-81

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SUMMARY

The discussion focuses on calculating the percentage abundance of the isotopes Br-79 and Br-81 based on their atomic weights and the average atomic weight of bromine. The correct approach involves using two variables to represent the abundances of each isotope, leading to the equations (x1)(78.9183) + (x2)(80.9163) = 79.904 and x1 + x2 = 1. The final calculated abundances are 50.66% for Br-79 and 49.33% for Br-81.

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Homework Statement


Naturally occurring bromine contains two isotopes; Br-79, which has a weight of 78.9183 and Br-81 with a weight of 80.9163. If the atomic weight of Br is 79.904, determine the % abundance of Br-79 and Br-81.

Homework Equations



To solve this equation I try to put the equation as

(x)(78.9183) + (x)(80.9163) = 79.904

The value of x = .499946789



The Attempt at a Solution



The answers were given because this is a practical exam I'm studying for. Can someone point me in the right direction. Something seems to be missing from the equation.


Br-81 49.33%
Br-79 50.66%
 
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Nevermind I found the answer.. Thank you
 
For the record:

sjung915 said:
(x)(78.9183) + (x)(80.9163) = 79.904

is wrong, as abundances of both isotopes are different, not identical - so you need two variables. The correct equation is

(x1)(78.9183) + (x2)(80.9163) = 79.904

and you need another equation:

x1 + x2=1
 

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