Manganese (Mn) :

Manganese was discovered in 1774 by Swedish chemist John Gottlieb Gahn. Its name is derived from Latin word magnes meaning magnet. Its principle ore pyrolusite is paramagnetic.   

Occurrence:

It is 12^th most abundant element on earth crust. Its important minerals and ores are pyrolusite (principal ore) while other ores are rhodochrosite, franklinite and manganite.

Characteristics:

(i) Symbol = Mn 

  (ii) Atomic Number = 25   

(iii) Luster = Silvery white 

  (iv) Group = VII-B              

(v) Period = 3^rd     

(vi) Melting point = 1518K or 1245^oC 

(vii) Boiling point = 2334K or 2061^oC            

(viii) Electronic configuration = 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d⁵

(ix) In Free State it exists only in meteors

(x) Oxidation states:

• It shows +2, +3, +4, +6 and +7. It has highest oxidation state in 3-d series which is +7.
• Oxidation state +2:  
• The most stable oxidation state of manganese is +2. Mn²⁺ ions are stable due to half filled d-orbital (4s⁰, 3d⁵). Mn²⁺ ion exist as pale pink coloured [Mn(H₂O)₆]²⁺.  The compounds of Mn²⁺ are called manganous compounds. e.g. MnO, MnCO₃, MnSO₄, MnCl₂.
• Oxidation state +3:   
•  The compounds of Mn³⁺ are called manganic compounds. Mn³⁺ ion is quite unstable in aqueous solution and readily changes to Mn²⁺ ion. Some compounds of Mn³⁺ are H₂Mn₂O₄, Mn₂(SO₄)₃.  
• Oxidation state +4:  
•   Compounds showing +4 oxidation state are limited in number. e.g. MnO₂.
• Oxidation state +6:     
•  Examples of compound showing +6 oxidation state are potassium manganate K₂MnO₄,  manganic acid H₂MnO₄.
• Oxidation state +7:   
• Compounds showing +7 oxidation state are strong oxidizing agents. e.g. Mn₂O₇, KMnO₄. Mn₂O₇ is an unstable oxide. 

Potassium permanganate (KMnO₄) as oxidizing agent:

e.g. (i) KMnO₄ oxidizes alkenes to their corresponding diols (glycols) both in acid medium as well as in alkaline medium. Colour change depends on medium.

Reaction in acid medium:

5CH₂ = CH₂ + 2MnO₄^– + 2H₂O + 6H⁺ → 5HO – CH₂ – CH₂ – OH + 2Mn²⁺     

Reaction in alkaline medium:

The manganate (VII) ions are first reduced to manganate (VI) ions. Solution colour turns green due to manganate (VI) ions.

CH₂ = CH₂ + 2MnO₄^– + 2OH^– → HO – CH₂ – CH₂ – OH + 2MnO₄^{2 –}  

Then further reduction occurs and insoluble manganese (IV) oxide is produced.

3CH₂ = CH₂ + 2MnO₄^– + 4H₂O → 3HO – CH₂ – CH₂ – OH + 2MnO₂ + 2OH^–  

 e.g. (ii) As oxidizing agent it redox titration (volumetric analysis):

                Potassium permanganate is used in estimation of Fe²⁺ compounds. Fe²⁺ compounds are reducing agents so they need oxidizing agent for their estimation and potassium permanganate is an oxidizing agent so it is used for their estimation.

MnO₄^–    +   8H⁺   +  5Fe²⁺   →    Mn²⁺   + 5Fe³⁺ +   4H₂O

Or  

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

Using following formula the amount of Iron (II) compound is determined.

                                    KMnO₄          FeSO₄

M₁V₁/   n₁      =              M₂V₂/ n₂

M₁V₁ / 1     =              M₂V₂/5

   Potassium permanganate is also used in estimation of oxalic acid. Oxalic acid is reducing agent so it need oxidizing agent for its estimation and potassium permanganate is an oxidizing agent so it is used for estimation of oxalic acid.

MnO₄^–    +      8H⁺  +  5(COO)₂^2– →   Mn²⁺      +  10CO₂ + 4H₂O                      

Or    

 2KMnO₄  + 3H₂SO₄ +  5(COOH)₂ → 2MnSO₄ + K₂SO₄ +  10CO₂ +  8H₂O

Using following formula the amount of Iron oxalic acid is determined.

   KMnO₄              Oxalic acid

    M₁V₁ /n1     = M2V2/n2                                 

  M₁V₁ / 1   = M2V2/5                                                

Uses of Manganese and its important compounds:

• Manganese is used in making steel. Its presence in steel makes the steel tough.
• Uses of KMnO₄:
• It is used as oxidizing agent for organic compounds.
• It is used as disinfectant.
• It is used for sterilization of water. In market it is called pinky. 
• It is used in oxidation reduction titration.
• Alkaline aqueous solution of KMnO₄ called Baeyer’s reagent is used for detection of carbon carbon double and triple bond.

Also Read !!

Transition Elements

• Manganese is used in making steel. Its presence in steel makes the steel tough.
• Uses of KMnO₄:
• It is used as oxidizing agent for organic compounds.
• It is used as disinfectant.
• It is used for sterilization of water. In market it is called pinky. 
• It is used in oxidation reduction titration.
• Alkaline aqueous solution of KMnO₄ called Baeyer’s reagent is used for detection of carbon carbon double and triple bond.

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