Sunday, September 1, 2013

Redox Reactions

                      Any chemical reaction in which the oxidation states of the atoms are changed is an oxidation-reduction reaction.This reactions are also known as redox reactions. Redox reactions involve the transfer of electrons between species. Industrial process of electroplating, Extraction of aluminium and sodium metals, manufactures of caustic soda, etc are also based upon the redox reactions. Redox reactions are also form the basis of electrochemical and electrolytic cells. The electron transfer system in cells and oxidation of glucose in the human body are example of redox reaction.
                      The term redox comes from two concepts involved with electron transfer, reduction and oxidation. It can be explained in simple terms.

  • Oxidation is a process of addition of oxygen  ( or ) removal of hydrogen ( or ) loss of electron ( or ) increase in oxidation state by a molecule, atom or ion.
  • Reduction is a process of removal of oxygen ( or ) addition of hydrogen ( or ) Gain of electrons ( or ) decrease in oxidation state by a molecule, atom or ion.                                 
Example of Oxidation-Reduction Reaction : ( Ionic Equation )
               The reaction between copper and silver in which copper is oxidized and silver is reduced. The ionic equation for this reaction is,

                              Cu (s) +2 Ag + →Cu2+ (aq)  +  2Ag (s)
The over all reaction may be written as two half-reactions.

Oxidation Reaction :
                              Cu (s) →Cu2+ + 2e-
    The above half reaction mention the solid copper is oxidized ( losing electron ) to form a copper ion with plus 2 charge.

Reduction Reaction :
                                   2Ag+(aq)  +  2e-  →  2Ag (s) 
Here, two silver ions are reduced to form a solid silver.
When adding the reactions together the electrons are canceled.
      Cu (s)  →  Cu2+ + 2e-

     2Ag+(aq)  +  2e-  →  2Ag (s
Cu (s) +2 Ag + →Cu2+ (aq)  +  2Ag (s)  

Note :
Copper metal is immersed in a solution of silver nitrate. The solution gradually acquires the blue color characteristic of the hydrated Cu2+ while the copper becomes coated with glittering silver crystals.

(The above figure is galvanic cell reaction. Its also referred as voltaic cell or Daniel cell.)

One more example for redox reaction :
    The reaction between hydrogen and fluorine in which hydrogen is being oxidised and fluorine is being reduced.
                                     H2 + F2  →  2HF

The over all reaction may be wrotten as two half reactions 
           H2    →   2H+  +  2e- ( oxidation )

           F2 + 2e-     →   2F-   ( Reduction )
Adding the reactions together the electrons are canceled.
                            H2    →   2H+  +  2e- ( oxidation )
                    F2 + 2e-     →   2F-   ( Reduction )
                      H2  +  F2  →   2H+  +  2F-

Ions combine to form a hydrogen fluoride. 
                        2H+  +  2F-    → 2HF
The overall reaction is,

               H2 + F2  →  2HF

No comments:

Post a Comment