# Why is the oxidation of Mn^(2+) in ACIDIC media represented differently to the oxidation of Mn^(2+) in an ALKALINE medium? What do we mean by H^+ or H_3O^+?

Mar 24, 2017

Because chemistry follows experiment...........

#### Explanation:

${H}^{+}$ is very much a conceptual particle. When we write ${H}^{+}$ in a reaction we mean the hydronium ion, ${H}_{3} {O}^{+}$, which AGAIN is a conceptual species. The actual species is (probably) a cluster of 3-4 water molecules, with an extra proton to give ${H}_{7} {O}_{3}^{+}$, or ${H}_{9} {O}_{4}^{+}$. The clusters exchange the proton between themselves. We write ${H}^{+}$ or ${H}_{3} {O}^{+}$ for convenience.

When we write a redox equation, of course we balance mass and charge, and the use of ${H}^{+}$ or ${H}_{3} {O}^{+}$ is a means to this end. It happens that in ACIDIC medium, $M {n}^{2 +}$, may be oxidized to $M n {O}_{4}^{-}$:

$M {n}^{2 +} + 4 {H}_{2} O \rightarrow M n {O}_{4}^{-} + 8 {H}^{+} + 5 {e}^{-}$

In alkaline media, $M {n}^{2 +}$ may be oxidized to $\text{manganate ion}$, $M n {O}_{4}^{2 -}$, which is $M n \left(V I +\right)$:

$M {n}^{2 +} + 8 H {O}^{-} \rightarrow M n {O}_{4}^{2 -} + 4 {H}_{2} O + 4 {e}^{-}$

$\text{Manganates}$ give green salts.

Mass and charge are balanced (I think) as required. Note that this representation follows the actual experiment, not vice versa.

If there is a further issue or query, fire away.