# Why is the oxidation number method useful?

##### 1 Answer
Oct 5, 2015

Oxidation number is useful in many ways: 1) writing the molecular formula for neutral compounds 2) species undergone reduction or oxidation 3) calculate calculate free energy

#### Explanation:

Suppose take example of potassium permangnate $K M n {O}_{4}$
In this example we know the potassium valency +1, whereas each oxygen atom valency is -2, therefore the oxidation number of Mn is +7

$K M n {O}_{4}$ is good oxidising agent. But its oxidation power depends on the medium

Acidic medium it transfer 5 electrons
$8 {H}^{+} + {\left[M n {O}_{4}\right]}^{-}$ + $5 {e}^{-}$ = MnO + 4${H}_{2} O$

Neutral medium three electrons are transferred
$4 {H}^{+} + {\left[M n {O}_{4}\right]}^{-}$ + $3 {e}^{-}$ = $M n {O}_{2}$ + 2${H}_{2} O$

Basic medium only one electron is transferred
$K \left[M n {O}_{4}\right] + {K}^{+} + {e}^{-}$ =${K}_{2} M n {O}_{4} + 2 {H}_{2} O$

It is strong oxidant in acidic medium, whereas mild in basic medium. Hence depending on the power of oxidation strength we can select the medium. This variation can be explained by oxidation number. The amount of $K M n {O}_{4}$ required is lower in acidic medium for oxidising same qunatity of Oxalic acid and higher in basic medium. This is explained based on the oxidation number.