Preparation Of KMnO4

Potassium Permanganate is an inorganic compound. The chemical formula of Potassium Permanganate is KMnO4.It is an odourless, purplish-black crystalline solid. It dissolves in water, forms ions K+ and MnO4, and makes a pinkish solution. It is termed one of the most important compounds on earth. Potassium Permanganate is also known as ‘Condy’s Crystals.’It is also called chameleon material. Preparation of potassium permanganate is done by mixing KOH with powdered manganese oxide and other oxidising agents. This is then boiled, and KMnO4  solution preparation takes place. While preparing potassium permanganate, first, potassium manganate is produced.

How to make potassium permanganate?

Potassium permanganate is an oxidising agent. When stored in proper conditions, it can easily retain its condition over a long time. The reaction due to permanganate solutions is relatively fast. Potassium permanganate is a complex tetrahedral compound. It is used in preparing chlorine gas and other oxidation reactions on a laboratory scale. It is used in making disinfectants, Baeyer’s reagent, and other oxidising purposes on an industrial scale. It is prepared by mixing MnO2 with an alkali metal hydroxide and an oxidising agent(O2 or KNO3). The reaction produces dark green K2MNO4, which disproportionates in a neutral or acidic solution to give permanganate. Potassium permanganate is produced by pyrolusite ore.

• Pyrolusite ore is combined with KOH(or K2CO3) in the presence of air or oxidising agents like KNO3 or KClO3  to form potassium permanganate K2MNO4 also called green mass.

2MnO2 + 4KOH + O2,  →  2K2MNO4  + 2H2O

• The green mass is then extracted with water, followed by chlorine oxidation, giving potassium permanganate as a product.

2K2MNO4  + Cl2   → 2KCl + 2KMNO4

When the solution is concentrated, dark purple potassium permanganate crystals are separated.

After the fusion and making of potassium permanganate, that is:

2MnO2 + 4KOH + O2,  →  2K2MNO4  + 2H2O

⇒ Potassium permanganate can be either made by Hcl or H2SO4:

• With HCl:

2K2MNO4 + 4HCl  →  2KMNO4  + H2O + MnO2 + 4KCl

• With H2SO4 :

3K2MNO4 + 2H2SO4    →  2KMNO4  + 2H2O + MnO2 + 2K2SO4

Manganate ions will be disproportionate to form potassium permanganate in neutral or acidic reactions. 

MnO4– + e–  →  MnO4-2 

MnO4-2  + 4H+ + 3e – →  2MnO4– + MnO2 + 2H2O 

MnO4-2  + 8H+ + 5e – → Mn+2  + 4H2O

Therefore, the preparation of potassium permanganate involves a reaction of MnO2 with KOH to give MnO4-2, followed by electrolytic oxidation of manganate to give permanganate ion, MnO4–after this, manganese ion salt gets oxidised by peroxodisulphate to permanganate ion as per the reaction given below.

2Mn+2 + 5S2O8-2 + 8H2O →  2MnO4–  + 10 SO4-2+ 16H+

Hence the dark purple coloured crystals of potassium permanganate are obtained. 

Oxidation processes :

Chemical oxidation:

In this potassium manganate is treated with ozone:

2 MnO4-2  + O3 + H2O →  2 MnO4– + 2OH– +O2

2 MnO4-2  + Cl2 →    2 MnO4– +  2Cl–

Electrolytic oxidation:

This aqueous solution of potassium manganate is oxidised in the presence of little alkali.

K2MnO4 ↔ 2K+ + MnO4-2 

H2O ↔ H+ + OH–

At the anode, Manganate ions are then converted into permanganate ions.

MnO4-2  ↔ MnO4– + e– 

Green                 purple

H2S is liberated at cathode:

2H+ + 2e–  →  H2 ↑

The purple-coloured solution is concentrated by evaporation and cooled down to form potassium permanganate crystals. 

Laboratory Preparation: 

In the laboratory manganese (II) ion salt is oxidised by peroxodisulphate to permanganate:

2Mn+2 + 5S2O8-2 + 8H2O →  2MnO4–  + 10 SO4-2+ 16H+

Preparation of potassium permanganate solution:

1. To prepare 1000 ml of 0.1 N KMnO4 solution, we need approximately 3.2 gm of potassium permanganate. Then transfer it into a beaker that has water and has to stir it completely using a glass rod until the crystals start breaking up. We need to allow it to stand for two days, then filter it using a volumetric flask, leaving undissolved residues in the beaker. This process is repeated several times until all the potassium permanganate solution is dissolved. The solution is then stored in a closed container.
2. 0.2 g of anhydrous sodium oxalate is dried and dissolved in 100mL of water and 7 ml of sulphuric acid. Then slowly, a permanganate solution is added; when the first few drops are added, we need to shake or stir it constantly. It will result in a slight pinkish colour. We need to repeat this; the endpoint will be achieved when a faint pink colour is observed for 30 seconds.

Conclusion:

Potassium Permanganate is a dark purple solid consisting of two ions: a potassium ion (K⁺) and a permanganate ion (MnO-2). It is a strong oxidising agent and also possesses medicinal properties, due to which it is extensively used to clean wounds and in dermatitis. Preparation of potassium permanganate is done by fusing powdered Pyrolusite ore (MnO2) with an alkali metal hydroxide like KOH in the presence of air or an oxidising agent like KNO3. It then leads to the formation of dark green potassium Manganate (K2MnO4), which is disproportionate either in a neutral or acidic medium and results in the formation of potassium permanganate. But before the preparation of potassium permanganate, KMnO4  solution preparation takes place. Either HCl or H2SO4 can prepare K2MnO4.