chemistry

Manganese-Important Transition Element

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 12th 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 = 3rd     

(vi) Melting point = 1518K or 1245o

(vii) Boiling point = 2334K or 2061oC            

(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+  

                      Intense purple                          light pink         

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 + 2MnO42   

                                                        Intense purple                                                        green

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

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

                                                       Intense purple                                                                   dark brown precipitate

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

Oxidizing agent                            Reducing agent

                                                           Light Green                  light pink          Yellowish Brown

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)22             →            Mn2+      +       10CO2 + 4H2O

Oxidizing agent                                Reducing agent                       light pink

Intense purple                                                                                                                                    

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.

Also Read !!

Transition Elements

Iron

Vanadium

Chromium

Coordination Compounds 

Peculiar Behaviour of Beryllium 

Group 1 Elements alkali Metals Occurrence, Physical and Chemical Properties, Reactivity and Compounds

Trends in the physical properties of period 3 elements

Trends in the chemical properties of period 3 elements

Anomalous Behavior of Lithium

Group IV-A Elements Properties

Group VII-A Elements Properties

Electron affinity trends

Ionization Energy Trends

Electronegativity – Definition, Periodic Trends ,Examples , Importance ,Electronegativity Difference

Ionic Bond

Covalent Bond

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5 replies »

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