Question

Calculate the atomic mass (average) of chlorine using the following data:
% Natural Abundance Molar Mass
$^{35}\text{Cl}$ 75.77 34.9689
$^{37}\text{Cl}$ 24.23 36.9659

Answer 1

The average atomic mass of chlorine

= [(Fractional abundance of $^{35}\text{Cl}$)(Molar mass of $^{35}\text{Cl}$) + (Fractional abundance of $^{35}\text{Cl}$)(Molar mass of $^{35}\text{Cl}$)]

$= \bigg[{(\frac{75.77 }{ 100})(34.9689 u)} + {(\frac{24.23 }{ 100})(36.9659 u)}\bigg]$
= 26.4959 + 8.9568
= 35.4527 u
∴ The average atomic mass of chlorine = 35.4527 u