AP CHAPTER 5 OUTLINE
OXIDATION-REDUCTION REACTIONS
I. Oxidation-Reduction Reactions
A. Oxidation-Reduction -- electron transfer reactions
1. Redox -- shorthand name
2. Oxidation -- loss of electrons
3. Reduction -- gain of electrons
4. Always occur together
a. LEO the lion goes GER -- Lose Electrons Oxidation, Gain Electrons Reduction
5. Oxidizing Agent -- electron acceptor substance
a. The oxidizing agent is the substance that is reduced
6. Reducing Agent -- electron donor substance
a. The reducing agent is the substance that is oxidized
B. Oxidation Numbers -- sytem used to keep tabs on electrons
1. Oxidation state -- same as oxidation number
2. A redox reaction is a chemical reaction in which changes in oxidation numbers occur
C. Assigning oxidation numbers!!
1. The oxidation number of any free element is zero (0)
2. The oxidation number for any simple, monatomic ion is equal to the charge of the ion
3. The sum of all oxidation numbers of the atoms in a molecule or polyatomic ion must equal the charge of the particle
4. In its compounds, fluorine bas an oxidation number of -1
5. In its compounds, hydrogen has an oxidation number of +1
6. In its compounds, oxygen has an oxidation number of -2
D. Oxidation Numbers and Redox Reactions
1. Oxidation is an increase in oxidation number
2. Reduction is a decrease in oxidation number
II. Balancing Redox Equations by the Ion-Electron Method
A. Basic Principles
1. divide the oxidation and reduction processes into individual equations that are balanced separately
a. called Half-reactions
2. Skeleton equation -- shows only the ions or molecules involved in the reaction
a. Balance each half reaction (balance both atoms and charge)
b. Balance charge by adding electrons
c. In any redox reaction, the number of electrons gained always equals the number lost
B. Reactions Involving H+ and OH-
1. H+, OH- and water play any important role in redox reactions, therefore we need to know whether the reaction occurs in an acidic or a basic solution
C. Balancing Redox Equation for Acidic Solutions!!
1. Divide the skeleton equation into half-reactions
2. Balance atoms other than H and O
3. Balance oxygen by adding H2O to the side that needs O
4. Balance hydrogen by adding H+ to the side that needs H
5. Balance the charge by adding electrons
6. Make the number of electrons gained equal the number lost and then add the two half-reactions
7. Cancel anything that is the same on both sides
D. Balancing Redox Equations for Basic Solutions (additional steps to acidic solutions)!!
8. Add to both sides of the equation the same number of OH- as there are H+
9. Combine H+ and OH- to form H2O
10. Cancel any H2O that you can
III. Reactions of Metals with Acids
A. The reaction of an acid with a metal is a redox reaction in which the metal os oxidized and the acid is reduced
1. Metal is the reducing agent, the H+ is the oxidizing agent
2. The products are always a metal salt and gaseous hydrogen
B. Oxidizing Power of Acids
1. Monoxidizing acids -- acids in which the anion is a weaker oxidizing agent than H+ (already a weak oxidizer)
a. The H+ ion will be reduced to H2 gas
b. Monoxidizing acids -- Hdrochloric acid, Sulfuric acid (aq), Phosphoric acid, most organic acids
3. Oxidizing acids -- acids in which the anion is a stronger oxidizing agent than H+
a. The anion will be reduced to a gas (NO2, SO2)
b. Oxidizing acids -- Nitric acid (conc.) and Sulfuric acid (conc.)
IV. Displacement of One Metal by Another from Compounds
A. Single replacement reaction -- reaction in which one element replaces another in a compound
1. Considered a redox reaction since there is a change in oxidation state
2. The more "active" element replaces the less "active" element in a compound
B. The Activity Series (easily oxidized)
1. Range of elements based on their ease of oxidation
C. Using the Activity Series
1. Used to make predictions on whether or not a reaction will occur
V. Molecular Oxygen as an Oxidizing Agent
A. Oxygen is a strong oxidizing agent
1. Combustion -- a rapid reaction of a substance with oxygen in which both heat and light are given off
2. Reaction with metals -- corrosion (rusting, tarnishing)
3. Reaction with nonmetals -- similar to reaction with metals
VI. Stoichiometry and Redox Reactions
A. Approached the same way we approached metathesis reactions and acid-base reactions
B. Using Redox Reactions in the Laboratory (Titrations)
1. No simple indicator that can be used to detect end point like in acid-base titrations
a. KMnO4 (Potassium permanganate) works as a good indicator in acid solutions
b. Powerful oxidizing agent, Mn+2 is colorless and MnO4- is a deep purple in solution
Outline based upon:
Brady, J. E., Holum, J. R., Russell, J. W. (2000). Chemistry: The Study of Matter and Its Changes. (3rd ed.). New York: John Wiley & Sons, Inc. pp. 193-220.
