Question

Bromine occurs in nature mainly in the form of two isotopes Br7935 and Br8135. If the abundance of Br7935 is isotope is 49.7% and that of Br8135​ isotope is 50.3% calculate the average atomic mass of bromine.

Answer 1

Atomic Mass for Bromine is 50.8

Explanation:

We know that % Mass + % Mass = Average of Atomic Mass

• Suppose x as % abundance for Br-79 and 1-x for Br-81

Br is $79. 904\ gmol^-^1$ on the periodic table (average atomic mass)

79.904% = x + (1 - x)

79.904% = (78.92x) + (80.92 (1 - x))

79.904% = 78.92x + 80.92 - 80.92x

79.904% - 80.92 = 78.92x

-1.016 = -2x

x = 0.508

• Use our x to find that % abundance of Br-79

x100%

0.508 100%  

= 50.8 % abundance

Use our x to find that % abundance of Br-79

(1 - x)100%

0.492 \times 100%

= 49.2% abundance

• The % abundance of the isotope with a mass of 78.92 amu has a % abundance of 50.8% and the isotope with a mass 80.92 amu has a % abundance of 49.2%