Question

What is the average atomic mass of chlorine if it has isotopes of masses $36.96590$ and $34.96885$, which are $24.47\%$ and $75.53\%$ abundant respectively?

Answer 1

Step1. Average atomic mass

• There are many isotopes for many naturally occurring elements.
• The average atomic mass of that element can be calculated by taking into consideration the existence of various isotopes and their relative abundance (percent occurrence).

Step2. Formula for average atomic mass

$\text{Average atomic mass}={\mathit{\text{f}}}_{\mathit{1}}{M}_1+f_2{M}_2+\dots +f_n{M}_n$

Here, $f_1,f_2,f_n$ represents the relative abundance of the isotope and $M_1,M_2,M_n$ is the atomic mass of the isotope.

Step3. Calculation of average atomic mass of chlorine

The average atomic mass of chlorine=$\left(36.96590\text{u}\right)\times \left(0.2447\right)+\left(34.96885\text{u}\right)\times \left(0.7553\right)$

=$9.045\text{u+26.4119 u}$

=$35.4569\text{u}$

Hence, the average atomic mass of chlorine is $35.4569\text{u}$.