How is the oxidation of "ferrous ion" to "ferric ion" by "permanganate ion" represented?

May 16, 2017

We write out the individual redox processes to get:

$M n {O}_{4}^{-} + 5 F {e}^{2 +} + 8 {H}^{+} \rightarrow M {n}^{2 +} + 5 F {e}^{3 +} + 4 {H}_{2} O \left(l\right)$

Explanation:

$\text{Oxidation reaction (i):}$

$F {e}^{2 +} \rightarrow F {e}^{3 +} + {e}^{-}$

$\text{Reduction reaction (ii):}$

$M n {O}_{4}^{-} + 8 {H}^{+} + 5 {e}^{-} \rightarrow M {n}^{2 +} + 4 {H}_{2} O \left(l\right)$

For both $\left(i\right)$ and $\left(i i\right)$, $\text{charge is balanced}$ and $\text{mass is balanced}$, as indeed they must be if we purport to represent chemical reality. The final redox reaction adds $5 \times \left(i\right) + \left(i i\right)$ so that electrons, conceptual particles, do not appear in the final redox equation:

$M n {O}_{4}^{-} + 5 F {e}^{2 +} + 8 {H}^{+} \rightarrow M {n}^{2 +} + 5 F {e}^{3 +} + 4 {H}_{2} O \left(l\right)$

Which is balanced (is it?) with respect to mass and charge. The reaction has a built in indicator in that $M n {O}_{4}^{-}$ in intensely purple, whereas the reduction product $M {n}^{2 +}$ is almost colourless. An endpoint could be vizualized.