How to Balance Redox Reactions

One of the hardest topics in high school chemistry is how to balance redox reactions, formally oxidation reduction reactions. The procedure to balance these types of reactions is simple if you can follow a few basic steps. A good knowledge of proceeding concepts and principles taught in the course is essential to be able to handle these types of problems.

Instructions

Difficulty: Challenging

1. Identify the atoms in the reaction that are changing oxidation state. This can be performed by calculating the charge on each atom in the equation. By comparing the charge on the atom before and after the reaction, you can tell which atoms are participating in the oxidation reduction reaction. All other atoms in the equation are simply spectator ions.
2. Separate out of the equation the two half-reactions for the atoms that are being reducted and the ones being oxidized. Once the reactions are written in the correct fashion there will be electrons added to left side of the reaction and electrons being produced on the right side of the equation. The common half reactions are listed on a table in the back of most chemistry textbooks.
3. Balance the half-reactions with respect to atoms. Make sure that an equal amount of each atom exists on both sides of the equation. At this point, you need to make sure that the number of electrons is equal on both sides of the equation. You may need to use a multiple number of oxidation half-reactions to produce the correct number of electrons required by the reduction half-reaction.
4. Balance the charge of each equation. The charge of each equation can be balanced by adding either hydrogen ions (+) or hydroxide ions (-) to either reaction. When hydrogen ions and hydroxide ions combine, they produce a water molecule, which has charge of zero.
5. Add the two half reactions back together exactly as you have them written at this point and check your work. Make sure that there are the same number and kind of atoms on each side of the equation. Make sure the overall charge of each side of the reaction is equal.

Tips & Warnings

• This is a list of charges that are almost always true: hydrogen atoms +1, oxygen atoms in solutions or compounds -2, alkali metals +1 and alkali earth metals +2. There are always a few exceptions so be careful.