Question

11. Calculate the atomic mass for the following isotopes of Chlorine with the following

Answer 1

Given Isotopes $\sf _{17}Cl^{35},_{17}Cl^{37}$

• Average atomic mass of Cl=35.453u

Now

Masses of isotopes are Cl-35 and Cl-37

Let

• %abundance of Cl-35 isotope be x
• % abundance of Cl-37 isotope =100-x

ATQ

$\\ \sf\longmapsto Average\:Atomic\:Mass=\dfrac{35x+(100-x)37}{100}$

$\\ \sf\longmapsto \dfrac{35x+(100-x)37}{100}=35.453$

$\\ \sf\longmapsto \dfrac{35x+3700-37x}{100}=35.453$

$\\ \sf\longmapsto \dfrac{-2x+3700}{100}=35.453$

$\\ \sf\longmapsto -2x+3700=100(35.453)$

$\\ \sf\longmapsto -2x+3700=3545.3$

$\\ \sf\longmapsto -2x=3545.3-3700$

$\\ \sf\longmapsto -2x=-154.7$

$\\ \sf\longmapsto 2x=154.7$

$\\ \sf\longmapsto x=\dfrac{154.7}{2}$

$\\ \sf\longmapsto x=77.35\%$

And

$\\ \sf\longmapsto 100-x=100-77.35=22.65\%$

• %abundance of Cl-35=77.35%
• %abundance of Cl-37=22.65%