Question

Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron (II) ions (ii) $S{O_2}$ and (iii) oxalic acid? Write the ionic equations for the reactions.

Answer 1

Hint: In order to solve this question, we will see what is potassium permanganate. It is a compound which is water soluble and its color is dark purple and it is odorless. We will see reactions with iron (II) ions and oxalic acid and sulphur dioxide. Before that we will begin with its commercial preparation.

Complete step by step solution:
The potassium permanganate has an ionic bond between the potassium cation and the permanganate anion.
The compound is prepared by mixing the solution of KOH with powdered manganese oxide in the presence of oxidizing agents like potassium chlorate. The next step is to boil the mixture till it evaporates and the residue of iron attains a paste like consistency.
$6KOH + 3Mn{O_2} + 6KCl{O_3}\xrightarrow[{}]{{}}3{K_2}Mn{O_4} + 6KCl + 3{H_2}O$
The product of the above reaction is potassium manganate which is green in color. The potassium manganate is boiled in large quantities with water and chlorine and oxidized air and carbon dioxide is passed till the liquid is converted into permanganate. The $Mn{O_2}$ formed is quickly removed to stop the breaking down of the permanganate.
$6{K_2}Mn{O_4} + 3C{l_2}\xrightarrow[{}]{{}}6KMn{O_4} + 6KCl$
The product formed is potassium permanganate.
Now the reaction of potassium permanganate with iron(II) ions.
In acidic medium the potassium permanganate oxidises iron(II) ions
The ionic reaction is given as
$2MnO_4^{2 - } + 16{H^ + } + F{e^{2 + }} \to 2M{n^{2 + }} + 8{H_2}O + 10F{e^{3 + }}$
The iron is oxidized from its second oxidation state to third oxidation state.
Now the reaction of sulphur dioxide with potassium permanganate, it oxidises the sulphur dioxide to sulphuric acid.
$2MnO_4^{2 - } + 5S{O_2} + 2{H_2}O \to 2M{n^{2 + }} + 5S{O_4}^{2 - } + 4{H^ + }$
Also, it oxidises oxalic acid to $C{O_2}$ and ${H_2}O$
The reaction is
$2MnO_4^{2 - } + 16{H^ + } + 5{C_2}{O_4}^{2 - } \to 2M{n^{2 + }} + 8{H_2}O + 10C{O_2}$

Note: As from the above reaction it is very clear that the $KMn{O_4}$ is a very strong oxidizing agent and when it reacts with other compounds it does not produce any toxic compound as by product. The permanganate is usually prepared from other minerals such as manganese oxide as above. During the above preparation $KMn{O_4}$ is obtained in the form of crystals.