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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. 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 a. Except O’s and H’s b. Balance O’s by adding H2O c. Balance H’s by adding H+ HNO3 + H2S S + NO Acidic Solution Balancing Redox Reactions in Basic Solutions 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 a. b. c. d. e. f. Except O’s and H’s Balance O’s by adding H2O Balance H’s by adding H+ Add OH to both sides to balance H+ Clean up H+ & OH- (by making water) Reduce/cancel excess H2O’s NO2 NO-2 + NO3-1 Basic Soln