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)
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.