Question

What is the number of moles of $KMn{{O}_{4}}$ that will be needed to react with one mole of sulphite ions in acidic solution?

Answer 1

Hint: Movement of electrons in the chemical reaction is called Oxidation.
Oxidation state can be described as the total number of electrons that atoms in a molecule can share, either gains or loses in order to form a chemical bond with another atom.

Complete answer:
$2KMn{{O}_{4}}+3{{H}_{2}}S{{O}_{4}}\to 5O+2MnS{{O}_{4}}+{{K}_{2}}S{{O}_{4}}+3{{H}_{2}}O$
In this reaction Potassium permanganate is reacting with sulfuric acid to produce Manganese Sulfate, Potassium Sulfate, Oxygen and water.
This is a Redox(oxidation-reduction) reaction:
$\begin{align}
  & 2M{{n}^{+7}}+10{{e}^{-}}\to 2M{{n}^{+2}}(reduction) \\
 & 5{{O}^{-2}}-10{{e}^{-}}\to 5{{O}^{0}}(oxidation) \\
\end{align}$
Ionic Equation is:
$2MnO_{4}^{-}+5SO_{3}^{2-}+6{{H}^{+}}\to 2M{{n}^{2+}}+5SO_{4}^{2-}+3{{H}_{2}}O$
So, Clearly, we can see that $5$moles of $SO_{3}^{2-}$ ion (sulfite ion) needs $2$moles of $MnO_{4}^{-}$(permanganate ion).
$5$ moles of $SO_{3}^{2-}$ ions are oxidized by $MnO_{4}^{-}$ ions = $2$ moles
$\therefore 1$ mole of $SO_{3}^{2-}$ ions is oxidized by $MnO_{4}^{-}$ ions =$\frac{2}{5}$moles
The Answer is $1$ mole of sulfite ion ($SO_{3}^{2-}$) will require $\frac{2}{5}$ moles = $0.4$moles of $KMn{{O}_{4}}$

Note:
-In acidic medium,$KMn{{O}_{4}}$(Potassium Permanganate) behaves as a strong oxidizing agent whereas in an alkaline and neutral medium it behaves as a weak oxidant.
-In organic chemistry Potassium Permanganate is mainly used in neutral or alkaline solutions. To break the carbon-carbon bonds acidified potassium permanganate is used as it is a destructively strong oxidizing agent in acidic medium.
-Also, Potassium Permanganate fades soon in the strong acids like sulfuric acid (${{H}_{2}}S{{O}_{4}}$) but in weak acids like acetic acid ($C{{H}_{3}}COOH$) it fades slowly.