L E O the Lion says G E R

L osing  E lectrons is O xidation

G aining E lectrons is R eduction

Steps for balancing Redox Reactions

1. Assign oxidation numbers to all chemicals in the equation. (Elements are 0 and compounds are 0, ions (if any) add up to their valence).

2. Connect and elements that change oxidation numbers left to right across the arrows in the chemical equation. 

Watch out for diatomic wimps. If one side of the bracket is connected to a wimp, double the other side of the bracket immediately.

3. Write an expression of how many electrons have changed places

4. Multiply if necessary to equalize or balance the number of electrons. Now bring the multiplier down as a coefficient in the chemical equation.

5. Now balance by inspection. Save Oxygen for 2nd to last. Save H for last.

AP students:

If the problem is "in acid environment" you add H⁺ as necessary to the left side of  the equation. This will make additional H₂O on the right side.

You may add H₂O to balance out O's on either side of equation.

In a basic environment proceed as you would in acid, but then after H's have been balanced add OH- to both sides of the equation to eliminate any free H+ by making waters. Cancel the number of waters appearing on both sides of the equation.

Sample Problem