Potassium Permanganate (KMnO4)

Preparation:- Commercially Pot. Permanganate is prepared from mineral pyrolusite (MnO₂) in the following steps:

a)Conversion of MnO₂ into potassium manganate

b) Oxidation of K₂MnO₄ into permanganate

2K₂MnO₄ + Cl₂ ⟶ 2KMnO₄ + 2KCl

Properties:-

1. Colour:- It is a deep purple black crystalline solid with M. Pt. 523K.
2. Solubility:- It is moderately soluble in water at room temp. and more soluble in  Hot Water.
3. Action of  Heat:- It forms different products at different conditions e.g.
4. Action of Conc. H₂SO₄:-

• In cold:-

2KMnO₄ + 2H₂SO₄ ⟶ Mn₂O₇ + 2KHSO₄ + H₂O  

• On warming:-

4KMnO₄ + 6H₂SO₄ ⟶ 2K₂SO₄ + 4MnSO₄ + 6H₂O + 5O₂

5. Oxidising Properties:- KMnO₄ acts as strong oxidizing agent in neutral, basic as well as acidic medium.

1. In neutral medium         2KMnO₄ + H₂O ⟶ 2KOH + 2MnO₂ + 3[O]

Eq. wt. in neutral medium:- (2 x (KMnO₄) / 3[O] x 8 = (2/3) (158/16) x 8 = 52.67

2. In basic medium:-           

2KMnO₄ + 2KOH ⟶ 2K₂MnO₄ + H₂O + O

K₂MnO₄ + H₂O ⟶ MnO₂ + 2KOH  + O  ] x 2

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2KMnO₄ + H₂O ⟶ 2KOH + 2MnO₂ + 3O 

The over all equation is similar to aqueous medium. Hence eq. wt. in basic medium is also 52.67. If the strong Alkali is used only the first feaction is occurs and the eq. wt. is 158.

iii.   In acidic Medium:-

2KMnO₄ + 3H₂SO₄ ⟶ K₂SO₄ + 2MnSO₄ + 3H₂O + 5 [O]

Eq. wt. in acidic medium = 2 x (KMnO₄) / 5[O] x 8 = (2 x 158)/(5 x 16) x 8 = 31.6

Note:- Eq. wt. is the wt. of substance which combines or displaced directly or indirectly 8 parts by wt. of oxygen, 35.5 parts by wt of chlorine or 1 part by wt. of hydrogen.

6. Examples of Oxidation:-

1. Oxidation of H₂S into S:-
2. Sulphur dioxide into H₂SO₄:-
3. Ferrous Sulphate into Ferric sulphate:-
4. H₂O₂ to H₂O and C
5. Potassium Iodide to Iodine:-

6. Uses: -

7. It is used as reagent in volumetric analysis.
8. It is used as an oxidizing agent in Laboratory.
9. It is used as a disinfectant and germicide.
10. It is used in purification of water.

Structure: Mn in MnO₄^- is sp³ hybridized. The four oxygens are tetrahedral attached to Mn.