Question

Assign the oxidation number to $\mathrm{Mn}$ in ${\mathrm{K}}_2{\mathrm{MnO}}_4$.

Answer 1

Solution:

• The oxidation number of $\mathrm{K}$ is $+1$
• The oxidation number of $\mathrm{O}$ is $-2$
• The only element left is $\mathrm{Mn}$, and we are unsure of its oxidation number.
• Assume that Mn has an oxidation number of $x$.
• Given that the molecule in ${\mathrm{K}}_2{\mathrm{MnO}}_4$ has a neutral charge,
• The entire oxidation number must thus be $0$.
• This means,
• $$\begin{gathered} +2\left(\mathrm{K}\right)+\mathrm{x}\left(\mathrm{Mn}\right)+\left(4\right)\left(\mathrm{O}\right)=0 \\ +2\left(1\right)+\mathrm{x}\left(\mathrm{Mn}\right)+\left(4\right)(-2)=0 \\ +2+\mathrm{x}\left(\mathrm{Mn}\right)=8 \\ \mathrm{x}=8-2 \\ \mathrm{x}=6 \end{gathered}$$

Final Answer:

In ${\mathrm{K}}_2{\mathrm{MnO}}_4$, $\mathrm{Mn}$'s oxidation number is $+6$.