Identifying the oxidation state of any individual element in a compound, ion or even and atom is crucial in this topic so we cannot move on until you can work it out confidently.

When you have oxidation states identified, you can see changes in state as either oxidation or reduction. Just as at GCSE, it is OILRIG, Oxidation is loss (of electrons) and Reduction in gain. Write half equations for each species then combine them to make full REDOX equations. Remember to multiply whole half equations to ensure that the numbers of electrons balance and can be cancelled out.

When creating a half equation, follow the same steps:

- Find out the oxidation states on both sides;
- Balance the element undergoing REDOX (only) on both sides;
- Add electrons appropriately (oxidation = right, reduction they are on the left);
- Balance out “O” by adding waters to the opposite side (if needed);
- Balance out the “H”s by adding H
^{+}s to the opposite side (if needed); - Cancel out any “duplicates” on opposing sides and check that the overall charge on the left is equal to the overall charge on the right.