Redox Reactions

REDOX-OXIDATION STATES Day One

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 1 st - 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 O 2 or others like P 4 and S 8. 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!!! Br 2 K +1 LiF CO 2 SO 4 -2 Na 2 O 2 Br = 0, Br= 0 1+ Li = 1+, F = 1- total = 0 O = -2 each = -4 Total = 0 C = +4 O= -2 ea. = -8 Total = -2 S = +6 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

½ REACTIONS 16.4 Day Two

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) Al = 0Ag +1 = +1 → Al +3 = +3Ag= 0 Al → Al +3 Ag + → Ag e- 1e- Al →Al +3 3 Ag + → 3Ag Al + 3Ag + → Al Ag

SnCl 3 + Fe  SnCl 2 + FeCl 2

½ REACTIONS ACIDIC AND BASIC SOLN Day Three

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 H 2 O c.Balance H’s by adding H +

HNO 3 + H 2 S  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.Except O’s and H’s b.Balance O’s by adding H 2 O c.Balance H’s by adding H + d.Add OH to both sides to balance H + e.Clean up H + & OH - (by making water) f.Reduce/cancel excess H 2 O’s

NO 2  NO -2 + NO 3 -1 Basic Soln