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Oxidation States

Sometimes, the transfer of electrons is very obvious like when ions are formed. Other times, it is less obvious as in the combustion of ethane. As a result, scientists came up with the concept of oxidation states, or oxidation number, to keep track of electron flow.

Rules for identifying oxidation numbers:

-All elements in its natural form have an oxidation number of zero (ex. C2, N).                  

– When there is no charge on the molecule, the sum of the oxidation number of the elements is equal to zero.          

-When there is a charge on the polyatomic ion the sum of all the oxidation number of the elements must be equal to the charge on the ion.        

– The oxidation number for all alkali metal ions is +1               

– The oxidation number for all alkali earth metals is +2       

– Hydrogen always has an oxidation number of +1 (exception: Hydrogen has an oxidation number of -1 when it is with boron in binary compounds)            

– Halogens have an oxidation number of -1 except when it is combine with another halogen.            

-Oxygen always has an oxidation number of -2 (exception: Oxygen has a oxidation number of -1 for peroxides)

Balancing Half-Reactions

Sometimes, redox reactions can be quite difficult to balance. Instead of proceeding through trial and error, a special technique for balancing redox reactions called the half-reaction method should be used.

Follow the 6 simple rules and you’re set!

1. Split the given reaction into 2 half reactions.

2. Balance the important elements.

3. Balance oxygen by adding H2O on required sides.

4. Balance H by adding H+ on required sides.

5. Balance the charge by adding e-.

6. Balance the equation by multiplying.

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