Question

Calculate the percentage of the naturally occurring isotopes $^{35}Cl$ and $^{37}Cl$ that accounts for the mass of chlorine taken as 35.45.

Answer 1

The mass of chlorine element is taken as 35. It exists in two major isotopes such as $Cl_{35}$ and $Cl_{37}$. We need to take the weighted average of both the isotopes in terms of the percentage of abundance that is present on the earth in order to get the average atomic mass of chlorine and it is calculated as follows

Let the percentage of $Cl_{35}$ be x, then $Cl_{37}$ be (100-x),

So,

$35.45=\frac{35x\times 37(100-x)}{100}$

Therefore, x = 77

Percentage of $Cl_{35}$ =77%  

Then, percentage of $Cl_{37}$ =23%