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Redox Reactions Day One REDOX-OXIDATION STATES 16.2-16.3 Oxidation-Reduction • Process of gaining or losing electrons • Oxidation: losing electrons • Reduction: Gaining Electrons OIL RIG How do we Identify if something is being reduced or oxidized? • Oxidation States (Oxidation Numbers) – Computed for each element based on the number of electrons assigned • There are FIVE (5) Rules for assigning Oxidation States Oxidation State RULES 1. Oxidation state of an atom in a free element is ZERO (0). 2. Hydrogen always has an oxidation number of (+1) , except in hydrides 3. Oxygen always has an oxidation number of (-2), except in peroxides Oxidation State Rules 4. The sum of oxidation states of all atoms in: – Molecule = (0) – Ion = charge of the ion 5. In their compounds, – Group I metal = (+1) – Group II metals (+2) Summary of Rules 1st- There are many that don’t have rules and are exceptions! • Rule Number One All free, uncombined elements have an oxidation number of zero. This includes diatomic elements such as O2 or others like P4 and S8. • Rule Number Two Hydrogen, in all its compounds except hydrides, has an oxidation number of +1 • Rule Number Three Oxygen, in all its compounds except peroxides, has an oxidation number of -2 • We can also assume in most cases group 1’s are +1 • With polyatomics- look at each ion separate and then assign numbers • Oxidation #’s are the # of atoms- not after multiplication. LETS TRY A FEW!!! • • • • • • Br2 K+1 LiF CO2 SO4-2 Na2O2 Br = 0, Br= 0 1+ Li = 1+, F = 1- total = 0 O = -2 each = -4 Total = 0 C = +4 O= -2 ea. = -8 S = +6 Total = -2 Na = +1ea. = +2 O = -2 ea. = -4 Na has priority so it sets the rule so O will have a -1ea so the total = 0 Identify Redox Reaction • You can identify a redox by checking to see if one compound was reduced and the other was oxidized. • Remember: – Oxidation = an increase in oxidation state – Reduction = a decrease in oxidation state Day Two ½ REACTIONS 16.4 Balancing Redox Reactions 1. Assign Oxidation Numbers 2. Split reaction into two ½ reactions 3. Balance only the atom undergoing the change 4. Count up the # of electrons transferred 5. Balance the electrons by multiplying the ½ rxn 6. Bring the equation back together 7. Balance the rest of the reaction Al(s) + Ag+1 Al+3 + Ag(s) Ag+1 = +1 → Al+3 = +3 Al = 0 Ag= 0 Al → Al +3 Ag + → Ag 0 +1 3+ 0 3e- 1eAl →Al +3 3 Ag +→ 3Ag Al + 3Ag+ → Al +3 + 3Ag SnCl3 + Fe SnCl2 + FeCl2 Day Three ½ REACTIONS ACIDIC AND BASIC SOLN Balancing Redox Reactions in Acidic Solutions 1. 2. 3. 4. 5. 6. Split reaction into two ½ reactions Balance all elements except H and O Add electrons to show lose or gain of charge Balance number of electrons Add Water to balance O Add H+1 to balance H ** NO DIFFERENCE THAN WHAT WE HAVE BEEN DOING!!!!!!!!!!! HNO3 + H2S S + NO Acidic Solution Balancing Redox Reactions in Basic Solutions 1. 2. 3. 4. 5. 6. Split reaction into two ½ reactions Balance all elements except H and O Add electrons to show lose or gain of charge Balance number of electrons Add Water to balance O Add H+1 to balance H 7. Neutralize H+1 by adding the appropriate amount of OH-1 to EACH SIDE NO2 NO-2 + NO3-1 Basic Soln