Determining what is being oxidized
 
How do I figure out what is being oxidized in the following example:  Zn (s) + Cu2+ (aq) --> Zn2+ (aq)  +Cu (s) ?
 
First, recall that oxidation mean a loss in the number of electrons. Second, assign oxidation numbers to each species in the equation. After doing this, compare the oxidation numbers on both sides of the equation to tell what is being oxidized.
On the left side:
Zn= 0
Cu2+= =2
On the right side:
Zn2+= +2
Cu= 0
Comparing the two side, we can see that Zn went from an oxidation state of 0, to an oxidation state of +2; this is a loss of electrons. Zn was oxidized in the reaction.
  

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