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Acidified Potassium Permanganate

One of the chemical compounds of potassium is called as potassium permanganate. The chemical formula of potassium permanganate is KMnO4. It acts as a strong oxidizing agent which was discovered in 1659. This compound has ability to add oxygen or remove hydrogen or remove electrons from an element or compound. KMnO4 (potassium permanganate) is composed of 1-Mn atom is surrounded by 4-O-atoms.

The molecular weight of KMnO4 is 158.04 g/mol with tetrahedral structure. The oxidation of iron can be done in the presence of potassium permanganate to form an insoluble manganese dioxide and iron oxide which can be removed by filtration. It has dark colour purple solid which form pink colour solution in water.

The colour of solution depends on the concentration of compound in solution. This compound has very useful for various applications such as for the treatment of water in pharmaceutical manufacture. It is used to oxidize Fe, Mn, H2S and ‘As’ impurities. 

The treatment of water with it also improves taste and odour. It is used as a pre-oxidant for disinfection by-product control. KMnO4 can help to produce high quality water which can easily meet drinking water standards. It mainly involves in the oxidation of functional groups like aromatic side chains to RCOOH, organic sulphides to sulphones which is used to produce antibiotics and tranquilizers.

The oxidation reaction of KMnO4 is effected by the pH of the solution as Mn can exist from 2+ to 7+ oxidation state. Out of that Mn7+ is the most potent oxidation state in both acid and alkaline medium. This oxidation process is widely used in organic synthesis such as phase transfer catalysis. For example the oxidation of ferrous sulphate with acidified potassium permanganate results the formation of ferric sulphate with manganese sulphate and potassium sulphate. The oxidation reaction can be written as given below;

8H2SO4 + 2KMnO4 + 10FeSO4  â†’ 2MnSO4 + 5Fe2(SO4)3 + 8H2O + K2SO4

The 0.1 M acidified potassium permanganate solution can be prepared with 1.6g of KMnO4 in 100mL water which is acidified by the addition of 5 mL of 1 M solution of sulphuric acid.  The acidification cannot be done with the help of hydrochloric acid as it gets oxidised to chlorine gas. On the contrary, the alkaline solution of KMnO4 can be prepared with the help of potassium permanganate and 2% sodium carbonate solution.
We cannot write one formula for acidified potassium permanganate as it is a mixture, not a pure compound.  Manganese exists in 7+ oxidation state in potassium permanganate which is reduced to colourless or pink Mn2+ ion in acidic medium. The ionic reaction can be written as given below;

MnO4- +  8H+  +   5e-  â†’  Mn2+  +  4H2O

In the titration of KMnO4 with iron (II) solution, we have to take permanganate solution in the burette and add slowly to the solution of iron (II) which acts as reducing agent. As the purpel colour solution is added to iron(II) solution, the purpel colour is discharged. The addition of excess of permanganate solution makes the solution pink.