Oxidation-Reduction Reactions --are reactions during which electrons are transferred from one reactant to another.  One reactant gets oxidized and one reactant gets reduced.  To be able to determine which is which, we must assign oxidation numbers to each element in the reaction.

              If the oxidation number increases during the reaction--that reactant is being oxidized

              If the oxidation number decreases during the reaction--that reactant is getting reduced 

Assigning Oxidation Number

Rules to memorize:

1) O = -2     H = +1 (most of the time)   F= -1

        Exceptions: O2 2- =peroxide and H 1- = hydride

2)  Elements = 0

3)  Ions = Their Charge

4)  The sum of the oxidation numbers must = the overall charge

 

A Nifty Way to Remember the Oxidation and Reduction facts is:   LEO the lion says GER

L-losing     E- electrons     O-oxidation

G-gaining    E-electrons     R-reduction

 

  • If the molecule gets oxidized then it is called the reducing agent
     

  • If the molecule gets reduced then it is called the oxidizing agent

 

Go to Oxidation Practice Problems