An element has two naturally occurring isotopes, isotope 1 with an atomic weight of 78.918 amu and isotope 2 with an atomic weight of 80.916 amu. If the average atomic weight for the element is 79.903 amu, calculate the fraction of occurrences of these two isotopes.

The fraction of isotope 1 is 50.7 % and fraction fraction of isotope 1 is 49.2 %.

Explanation:

Given that

Weight of isotope 1 = 78.918 amu

Weight of isotope 2 = 80.916 amu

Average atomic weight = 79.903 amu

Lets take fraction of isotope 1 is x then fraction of isotope 2 will be 1-x.

The total weight will be summation of these two isotopes

79.903 = 78.918 x + 80.916 (1-x)

By solving above equation

80.916 - 79.903 = (80.916-78.918) x

x=0.507

So the fraction of isotope 1 is 50.7 % and fraction fraction of isotope 1 is 49.2 %.