Chlorine exists in two isotopic forms ${ }^{35} \mathrm{Cl},{ }^{37} \mathrm{Cl}$. If average atomic mass of chlorine is 35.5 , what is the percentage abundance of these isotopes respectively?

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Aicharya · Accepted Answer

Average atomic mass atomic mass of ${ }^{35} \mathrm{Cl} \times$ percentage $=\frac{+ \text { atomic mass of }{ }^{37} \mathrm{Cl} \times \text { percentage }}{100}$
Let the $\%$ abundance of ${ }^{35} \mathrm{Cl}$ isotope $=x$. $\%$ abundance of ${ }^{37} \mathrm{Cl}$ isotope $=100-x$. Average atomic mass $=35.5$ From formula, Average atomic mass $\begin{aligned} & =\frac{35 \times x+37 \times(100-x)}{100}=35.5 \\ & 35 x+3700-37 x=35.5 \times 100 \\ & -2 x=-3700+3550 \\ & 2 x=150 \\ & x=75 \end{aligned}$
Percentage abundance of ${ }^{35} \mathrm{Cl}=75 \% \text { and }{ }^{37} \mathrm{Cl}=(100-75)=25 \%$

Chlorine exists in two isotopic forms ${ }^{35} \mathrm{Cl},{ }^{37} \mathrm{Cl}$. If average atomic mass of…

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