Question

$Cr{O}_4^{2-}$ is a strong oxidizing agent but $Mn{O}_4^{2-}$ is not. Explain why?

Answer 1

For $Cr{O}_4^{2-}$

Let the oxidation state of $Cr=x$

$x+4(-2)=-2$

$x=+6$

For $Mn{O}_4^{2-}$

Let the oxidation state of $Mn=x$

$x+4(-2)=-2$

$x=+6$

Since the oxidation of both $Mn$ and $Cr$ is in the $+6$ oxidation state. But $C{r}^{+6}$ is a strong oxidising agent as compared to $M{n}^{+6}$ due to its higher standard reduction potential as compared to $M{n}^{+6}$.

The reduction potential of $M{n}^{+6}=1.52V$

The reduction potential of $C{r}^{+6}=1.33V$

Due to a higher reduction potential of $C{r}^{6+}$, it gets easily reduced and acts as a strong oxidizing agent.