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Balancing Redox Reaction Equations Chapter 9.2 Two Methods for Balancing 1. The Half-Reactions Method 2. The Oxidation Numbers Method • Both methods are based on the idea that electrons are neither created or destroyed during a redox reaction. They are simply transferred from the species being oxidized to the species being reduced • You must be able to balance redox reaction equations using both methods • You must be able to balance redox reaction equations in both acidic solution and basic solution The Half-Reactions Method 1. Identify and write down the unbalanced half-reactions (do this by first assigning oxidation numbers) 2. Balance atoms and charges in each half-reaction (use H2O to balance O, H+ to balance H, and e- to balance charge) 3. Multiply each half reaction by an integer such that the number of electrons cancel 4. Add the half-reactions and cancel 5. For reactions that occur in basic solution follow this additional step: Add OH- to both sides for every H+ present, combining to yield H2O on the H+ side then cancel if necessary The Half-Reactions Method CuS(s) +NO3-(aq) Cu2+(aq) +SO42-(aq) +NO(g) The Oxidation Numbers Method 1. Assign oxidation numbers and determine the atom that is oxidized and the atom that is reduced 2. Determine the number of electrons lost or gained per atom 3. Determine the number of electrons lost or gained per reactant molecule 4. Multiply by an integer such that the number of electrons cancels 5. Use these integers as coefficients for the reactants 6. Balance atoms (use H2O to balance O and H+ to balance H) 7. For reactions that occur in basic solution follow this additional step: Add OH- to both sides for every H+ present, combining to yield H2O on the H+ side then cancel if necessary The Oxidation Numbers Method BH4- +ClO3- H2BO3- +Cl- HOMEWORK Required Reading: p. 608-617 (remember to supplement your notes!) Questions: p. 613 #1-6 p. 616 #1,2 p. 617 #1-10