An acidic solution contains $2.68 imes 10^{-3}$ moles of an ion $A^{n+}$. This solution requires e

Question

An acidic solution contains $2.68 	imes 10^{-3}$ moles of an ion $A^{n+}$. This solution requires exactly $1.61 	imes 10^{-3}$ moles of $	ext{MnO}_4^-$ for the complete oxidation of $A^{n+}$ to $	ext{AO}_3^-$. Find the value of $n$.

Professor PC Thomas Classes · Answer

In $	ext{AO}_3^-$, the oxidation state of $A$ is $+5$. The change in oxidation state for $A^{n+}$ is $(5 - n)$. 
In acidic medium, $	ext{MnO}_4^-$ reduces to $	ext{Mn}^{2+}$ (change of $5$). 
By equating equivalents: $2.68 	imes 10^{-3} 	imes (5 - n) = 1.61 	imes 10^{-3} 	imes 5$. 
$5 - n = \frac{1.61 	imes 5}{2.68} = \frac{8.05}{2.68} \approx 3$. 
$5 - n = 3 \implies n = 2$.