We can get one more piece of information from 
our analysis of oxidation states.  That is the 
number of electrons gained or lost.  We’ll still 
assign oxidation states and determine if a 
process is reduction or oxidation by looking at 
the direction of change, more negative or more 
positive.  But we can tell the number of 
electrons gained or lost by the change in the 
oxidation state.  By how many units does the 
oxidation state change?  Let’s look at a couple 
of examples to see how this works.  Again we 
have our rules of assigning oxidation states.  
Hopefully you know most of them by now.  The 
first example is simple.  Cobalt two plus going 
to cobalt.  The oxidation states are assigned 
using rules three and one, so the ion is plus 
two and the element is zero.  The oxidation 
state is going less positive, which is the same 
as more negative.  Gaining negatives, or 
gaining electrons, is a reduction.  But notice 
that the oxidation state changes by two units 
from plus two to zero.  So this is a two electron 
reduction.  Our next example has methane 
going to carbon dioxide.  We can assign the 
oxidation states of hydrogen and oxygen by 
rule.  That leaves carbon with an oxidation 
state of minus four in methane and plus four in 
carbon dioxide.  Clearly this equation is not 
fully balanced, since hydrogen and oxygen are 
not balanced.  But that’s really immaterial, 
since we are looking at carbon, which changes 
by going more positive by eight units.  More 
positive is an indication of losing electrons, so 
this is an eight electron oxidation.
