Balancing Redox Reactions

Question 1

Describe the Half-Reaction Method for balancing redox reactions in acidic conditions

Answer 1

• Identify the species for the oxidation and reduction and write them as two separate half reactions (they will not be balanced at this point).
• For each half-reaction, balance all elements except for hydrogen and oxygen.
• Next, balance the oxygens in the reaction by adding H2O.
• Now finish by balancing the hydrogens using H+.
• Now total the charge on each side of the reaction and balance the charge using electrons (e–).
• Make the electron count match in the reduction and the oxidation by multiplying one or both of the balanced half-reactions by whole numbers to equalize the number of the electrons.
• Now combine the two reactions to make your overall redox reaction. Cancel any possible species that are on both sides of the equation (H2O and/or H+).
• Now do a final overall check by making sure that all the elements and charge are balanced on each side of the reaction.

Question 2

Describe the Half-Reaction Method for balancing redox reactions in basic conditions

Answer 2

• Add the same number of moles of OH- to the side of the equation with H+ so that the acid is neutralized into water (H2O).
• Add the same number of OH– to the other side of the reaction.
• On the side with both H+ and OH–, cross both of them out and replace with the same number of moles of H2O. This is how we switch from acidic to basic conditions.
• Now check, and cancel out any waters that appear on both sides of the equation. H2O should only be on one side of the equation.
• Double check that all elements and charge are balanced.