Oxidation-Reduction Reactions : Oxidation-Reduction Reactions LEO SAYS GER
Oxidation and Reduction (Redox) : Oxidation and Reduction (Redox) Electrons are transferred Spontaneous redox rxns can transfer energy
Electrons (electricity)
Heat Non-spontaneous redox rxns can be made to happen with electricity
Oxidation Reduction Reactions(Redox) : Oxidation Reduction Reactions(Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:
LEO says GER : : LEO says GER : Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced
Not All Reactions are Redox Reactions : Not All Reactions are Redox Reactions Reactions in which there has been no change in oxidation number are not redox rxns. Examples:
Rules for Assigning Oxidation NumbersRules 1 & 2 : Rules for Assigning Oxidation NumbersRules 1 & 2 The oxidation number of any uncombined element is zero 2. The oxidation number of a monatomic ion equals its charge
Rules for Assigning Oxidation NumbersRules 3 & 4 : Rules for Assigning Oxidation NumbersRules 3 & 4 3. The oxidation number of oxygen in
compounds is -2 4. The oxidation number of hydrogen in compounds is +1
Rules for Assigning Oxidation Number Rule 5 : Rules for Assigning Oxidation Number Rule 5 5. The sum of the oxidation numbers in the formula of a compound is 0 2(+1) + (-2) = 0
H O (+2) + 2(-2) + 2(+1) = 0
Ca O H
Rules for Assigning Oxidation NumbersRule 6 : Rules for Assigning Oxidation NumbersRule 6 6. The sum of the oxidation numbers in the
formula of a polyatomic ion is equal to
its charge X + 3(-2) = -1
N O X = +5 X = +6 X + 4(-2) = -2
S O
Reducing Agents and Oxidizing Agents : Reducing Agents and Oxidizing Agents The substance reduced is the oxidizing agent
The substance oxidized is the reducing agent Sodium is oxidized – it is the reducing agent Chlorine is reduced – it is the oxidizing agent
Trends in Oxidation and Reduction : Trends in Oxidation and Reduction Active metals:
Lose electrons easily
Are easily oxidized
Are strong reducing agents Active nonmetals:
Gain electrons easily
Are easily reduced
Are strong oxidizing agents
Electrochemical Terminology : Electrochemical Terminology Half-cell: a metal electrode in contact with a solution of its own ions Electrode: A conductor used to establish contact with a nonmetallic part of a circuit, such as an electrolyte Anode: The electrode where oxidation takes place Cathode: The electrode where reduction takes place
Voltaic Cells : Voltaic Cells Voltaic cells: Electrochemical cells in which a spontaneous redox reaction can be harnessed to produce an electric current. Anode:
negative Cathode:
positive
Zinc – Copper Battery : Zinc – Copper Battery
Zinc-Carbon Dry Cell Battery : Zinc-Carbon Dry Cell Battery
Mercury Dry Cell Battery : Mercury Dry Cell Battery
Lead Storage Automotive Battery : Lead Storage Automotive Battery
Electrolytic Cells : Electrolytic Cells Electrolytic cells: Electrochemical cell in which an electric current is used to drive a non-spontaneous process Cathode:
negative Anode:
positive
Electrolysis of H2O : Electrolysis of H2O 2H2O 2H2 + O2 Electrolyte is usually dilute sulfuric acid
Electroplating of Silver : Electroplating of Silver Cathode is the object to be plated Anode is a piece of the plating metal Solution contains ions of the plating metal
Standard Reduction Potentials : Standard Reduction Potentials
Measuring Electrode Potential : Measuring Electrode Potential 1. H2 Electrode is assigned a potential of zero volts 2. Second electrode is placed in a solution of its own ions 3. Reduction potential of second electrode is measured.