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Chemistry of vanadium, chromium, manganese, iron, copper and their compounds

 Vanadium

It is a silvery white metallic element discovered by address manual in 1801 as a form of chromium.

 In 8030 nails Gabriel work on vanadium. Vanadium shows -1,  0, + 1, + 2, + 3  + 4 and + 5 oxidation states. It is a very unstable in lower oxygen state and act as reducing agent. 

The most stable oxidation states are  + 4 and + 5.

Reason: It uses d-orbital electrons in addition to s electrons in bond formation.

The energy of n-1d orbitals and ns orbitals  are very close to each other. Therefore, in higher oxidation states, both n-1 d  and ns electrons are involve in bond formation.

V(-1) Compound: [V(CN)5(NO)]-5, [V(CO)6]-1

V(0) Compound: V(CO)6, V(dipy)3

V(1) Compound:V2O[V(dipy)3]

V(2) Compound: VO, V2O2, VX2, VSO4.7H2O

V(3) Compound:

V(4) Compound:

V(5) Compound:

example 

V2O5

It is a yellow red poisonous powder having melting point 670 oC. 

It is slightly soluble in water and produce pale yellow solution which is acidic in nature.

It undergoes reversible dissociation in temperature range of 700 to 1125oC.

At 700 - 1125 oC.

Colors of vanadium in different oxidation  states


Vanadium pentoxide acts as oxidizing agent

V2O5   +     6HCl    --------------------->   VOCl3  +    H2O    +    Cl2

V2O5   +     6HNO3 --------------------->   VHO3    +   N2O5

V2O5 as a catalyst:

In contact process for manufacturing of H2SO4 , SO2  has to be converted into SO3 .

Mechanism:

SO2   +  V2O5  ------------------->   SO3   +   V2O4

V2O4   +  1/2O2 ------------------->  V2O5

Chromium:

It is a shining metallic corrosion resistance element. 

Oxidation of Cr from Cr (III) to Cr (VI)

[Cr(H2O)6]3+ (purple)   +   3OH-  --------->  [Cr(H2O)3(OH)] (green ppt) +3H2O

[Cr(H2O)3(OH)3] (green ppt) + 3OH1- ---------> [Cr(OH)6]3+ green soln.

[Cr(OH)6]3+ green +  H2O2  --------> CrO42-  (yellow) +  2OH1-  +  8H2O

 Chromium(VI) chemistry

CrO42- (yellow)  +   2H+   --------->  Cr2O72- (green)  +    H2O

Cr2O72-  (green)  +    0H-  --------->  CrO42- yellow   +   7H2O   

 

Reaction with Zn

K2CrO4  +   2Zn2+   +    H2O ---------Zn(OH)2  +  ZnCrO4  +  H2O

Reaction with acid

K2CrO4   +   5H2SO4 ---------  > K2SO4  +  Cr2(SO4)3  +  5H2O + 3[O]

Potassium dichromate as oxidizing agent

Cr2O72-  +   14H+  +6e-   ----------  >  2Cr3+   +   7H2O

Reaction with Zn

Cr2O72-  +   14H+  + 3Zn  ----------  >  2Cr3+    +   H2O  +  3Zn2+ 

Reaction with oxalic acid

K2Cr2O7  +  14H2SO4  +  (COOH)2-------- > K2SO4  +   Cr2(SO4)3  +  CO2  + 7 H2O

Reaction with Mohr’s salt

K2Cr2O7  +  14H2SO4  +  FeSO4.H2O  +   6(NH4)2SO4-------- > K2SO4  +   Cr2(SO4)3  +  Fe3(SO4)2  + 7H2O + (NH4)2SO4

 

Manganese (Mn)

It is a silvery metallic element.

Oxidation state

Manganess can exist in number of oxidation states. The oxidation state are +3, +4, +7

Mn as oxidizing agent

In alkaline medium

2KMnO4  +  2KOH  ------- > K2MnO4  +  H2O  +  [O]

Purple/pink                              Green

K2MnO4  +   H2O  --------  > 2MnO2 +    4KOH  +  [O]

                                                 Brown

 Fe (Iron)

Fe exist in common oxidation state +2 and +3.

Fe2+    ---------- > F3+   e-

Catalytic properties


When Fe2+ acts as a catalyst, following mechanism has been proposed.

Mechanism I

  S2O82-   +   Fe2+   ---------  >  SO42-    +   2Fe3+

2Fe3+     +  2I-     -----------  > 2Fe2+      +   I2

When Fe3+ acts as a catalyst, following mechanism has been proposed

Mechanism II

2Fe3+     +  2 I-       -----------  > 2Fe2+    +   I2

S2O82-    +   Fe2+   ---------  >   SO42-     +   2Fe3+

 

Reaction with NaOH

[Fe(H2O)6]2+   2OH-    ---------  >   [Fe(H2O)4(OH)2]   +  2H2O

Green solution                                    Green ppt

 [Fe(H2O)6]3+    3OH-   ---------  >   [Fe(H2O)3(OH)3]   +  3H2O

Yellow                                                  Brown ppt

 Reaction with NH3

Ammonia as a base

[Fe(H2O)6]2+   2NH3  ---------  >   [Fe(H2O)4(OH)2]   +  2H2O

Green solution                                    Green ppt

[Fe(H2O)6]3+   2NH3   ---------  >   [Fe(H2O)3(OH)3]   +  3NH4+

Green solution                                    Red brown ppt

Reaction with CO32-, SCN-

With CO32-

 Fe2+ +   CO32-  ---------- > FeCO3

[Fe(H2O)6]3+    3CO32-    ---------  >   [Fe(H2O)3(OH)3]   +  3CO2  + 3H2O

[Fe(H2O)6]3+    SCN-   ---------  >   [Fe(H2O)5(SCN)]2+    + 3H2O

 

Copper 

It is a brown red metallic element and it is one of the most wild used element.

The oxidation states of copper are +1 (cuprous Cu+) and +2 (cupric Cu2+).  The  most cuprous compounds are usually colorless and diamagnetic as 3d orbital is completely filled (Cu+ = 3d10)

Most of the cupric compounds are colorless while the hydrated cubic compound are blue due to formation of hydrated ion [Cu(H2O)4]2+ or Cu(H2O)6]2+.

Solution of salts are acidic in nature due to hydrolysis.

Cu2+  +  H2O  -------------->   [Cu(OH)]+   +   H+

Reactions of Cu(II) with hydroxide

[Cu(H2O)6] +   NaOH   ---------->   [Cu(H2O)4(OH)2]

Reaction of hexaaquacopper(II) ion with ammonia

i. Ammonia as a base

[Cu(H2O)6]2+.   +2NH3 (limited) --------------> [Cu(H2O)4(OH)2] (blue)  + NH4+

ii. Ammonia as a ligand

[Cu(H2O)6]2+.   +4NH3 (excess) --------------> [Cu(NH3)4(H2O)2]2+.  + 4H2O

Reaction with carbonates

Cu2+  +   CO32-  ------------> Cu CO3 (Blue ppt)




 

 





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