Question

What is the oxidation number of manganese in ${\mathrm{MnO}}_4^{-}$, ${\mathrm{Mn}}_2{\mathrm{O}}_3$, and ${\mathrm{MnO}}_2$?

Answer 1

Oxidation number: Oxidation number denotes the oxidation state of an element in a compound ascertained according to a set of rules formulated on the basis that electron pair in a covalent bond belongs entirely to a more electronegative element.

Part 1: Calculating the oxidation number of Manganese(Mn) in ${\mathrm{MnO}}_4^{-}$:

The oxidation state of Oxygen(O) = -2

The charge on ${\mathrm{MnO}}_4^{-}=-1$

Consider the oxidation state of Manganese(Mn) = x

Now,

$$\begin{gathered} x-2\times 4=-1 \\ x=-1+8 \\ x=+7 \end{gathered}$$

So, the oxidation number of manganese $\left(\mathrm{Mn}\right)$ in potassium permanganate${\mathrm{MnO}}_4^{-}$ is $+7$.

Part 2: Calculating the oxidation number of manganese $\left(\mathrm{Mn}\right)$ in ${\mathrm{Mn}}_2{\mathrm{O}}_3$

The oxidation state of Oxygen(O) = -2

Consider the oxidation state of Manganese(Mn) = x

Now,

$$\begin{gathered} x\left(2\right)-2\times 3=0 \\ x=+3 \end{gathered}$$

So, the oxidation number of manganese $\left(\mathrm{Mn}\right)$ in potassium permanganate${\mathrm{Mn}}_2{\mathrm{O}}_3$ is $+3$.

Part 3: Calculating the oxidation number of manganese $\left(\mathrm{Mn}\right)$ in ${\mathrm{MnO}}_2$

The oxidation state of Oxygen(O) = -2

Consider the oxidation state of Manganese(Mn) = x

Now,

$$\begin{gathered} x-2\times 2=0 \\ x=+4 \end{gathered}$$

So, the oxidation number of manganese $\left(\mathrm{Mn}\right)$ in potassium permanganate${\mathrm{MnO}}_2$ is $+4$.

Hence, the oxidation number of manganese in ${\mathrm{MnO}}_4^{-}$, ${\mathrm{Mn}}_2{\mathrm{O}}_3$, and ${\mathrm{MnO}}_2$ are $+7$, $+3$, and $+4$ repectively.