Chapter 11 Oxidation and Reductions Charge the World Lecture Presentation Chapter 11 Oxidation and Reductions Charge the World Bradley Sieve Northern Kentucky University Highland Heights, KY

11.1 Losing and Gaining Electrons Oxidation Reactant loses one or more electrons Reduction Reactant gains one or more electrons Oxidation and reduction always occur together When lost, electrons must go somewhere

11.1 Losing and Gaining Electrons Consider Na(s) reacting with Cl(g) Electrons transfer from Na to the Cl atoms 2Na(s) + Cl2(g)  2NaCl(s) + heat 2Na(s)  2Na+ + 2e– Oxidation Cl2(g) + 2e–  2Cl– Reduction

11.1 Losing and Gaining Electrons Half-Reaction Reactions showing the change in relation to one element only Excellent at showing which element gains electrons and which one loses electrons 2Na(s)  2Na+ + 2e– Oxidation Cl2(g) + 2e–  2Cl– Reduction

11.1 Losing and Gaining Electrons 2Na(s) + Cl2(g)  2NaCl(s) + heat Reducing agent causes the reduction on another element Na in this example is the reducing agent Oxidizing agent causes the reduction on another element Cl in this example is the oxidizing agent

11.1 Losing and Gaining Electrons Helpful mnemonics Leo the lion went “ger” Leo is “Loss of electrons is oxidation” ger is “gain of electrons is reduction” OIL RIG Oxidation is loss of electrons Reduction is gain of electrons

Concept Check True or false: Reducing agents are oxidized in oxidation-reduction reactions. Oxidizing agents are reduced in oxidation-reduction reactions.

Concept Check Both statements are true.

11.1 Losing and Gaining Electrons Indicators of an oxidation-reduction reaction Changes in ionic states of elements The gain or loss of oxygen atoms Gain or loss of H atoms

Concept Check In the following equation, is carbon oxidized or reduced? CH4 + 2O2  CO2 + 2H2O

Concept Check As the carbon of methane, CH4, forms carbon dioxide, CO2, it is losing hydrogen and gaining oxygen, which tells us that the carbon is being oxidized.

11.2 Harnessing the Energy of Flowing Electrons Electrochemistry The study of the relationship between electrical energy and chemical change Oxidation-reduction reactions can generate electricity Flow of electrons results in electrical charges

11.2 Harnessing the Energy of Flowing Electrons

11.2 Harnessing the Energy of Flowing Electrons

11.3 Batteries Consume Chemicals to Generate Electricity Examples of an oxidation-reduction in one container Can be either disposable or rechargeable Materials that oxidize and reduce each other are connected in a way that allows electron flow

11.3 Batteries Consume Chemicals to Generate Electricity Dry-Cell Battery Invented in the 1860s Cheapest disposable battery Zinc container filled with NH4Cl, ZnCl2, and MnO2 Contains a graphite rod to facilitate electron motion

11.3 Batteries Consume Chemicals to Generate Electricity

11.3 Batteries Consume Chemicals to Generate Electricity Electrodes of a dry-cell battery Cathode Electrode where chemicals are reduced Carries a positive charge (+) Anode Electrode where chemicals are oxidized Carries a negative charge (–)

11.3 Batteries Consume Chemicals to Generate Electricity Chemistry of the dry-cell battery At the anode, zinc is oxidized Zn(s)  Zn2+(aq) + 2e– Oxidation

11.3 Batteries Consume Chemicals to Generate Electricity Chemistry of the dry-cell battery At the cathode, reduction occurs 2NH4+ + 2e–  2NH3 + H2 Reduction which then reacts with ZnCl2 and MnO2 ZnCl2(aq) + 2NH3(g)  Zn(NH3)2Cl2(s) 2MnO2(s) + H2(g)  Mn2O3(s) + H2O(l)

11.3 Batteries Consume Chemicals to Generate Electricity

11.3 Batteries Consume Chemicals to Generate Electricity Alkaline Battery More expensive, but more consistent voltage Utilizes a strongly alkaline paste Zn(s) + 2OH–(aq)  ZnO(s) + H2O(l) + 2e– 2MnO2(s) + H2O(l) + 2e–  Mn2O3(s) + 2H2O(l)

11.3 Batteries Consume Chemicals to Generate Electricity Other types of disposable batteries Mercury batteries Use HgO instead of MnO2 Concerns about environmental hazards Lithium batteries Lithium is electron’s source instead of zinc Maintains higher voltage and makes lighter batteries

11.3 Batteries Consume Chemicals to Generate Electricity Rechargeable Batteries Contain a reversible set of oxidation and reduction reactions One example is NiMH Utilizes nickel metal and water reactants Produces nickel hydride and hydroxide ion Traditional car batteries are another type utilizing lead compounds

11.3 Batteries Consume Chemicals to Generate Electricity Rechargeable lithium-ion batteries Widespread use, including computer laptops and cell phones Hybrid cars use lithium phosphate batteries

Concept Check What chemicals are produced as a nickel- metal hydride battery is recharged?

Concept Check The chemicals are nickel hydride, H:Ni, and hydroxide ions, OH−.

11.4 Fuel Cells Consume Fuel to Generate Electricity Device that converts energy of fuel to electrical energy Consumes a continuous supply of fuel to produce electricity One common type is the hydrogen–oxygen fuel cell

11.4 Fuel Cells Consume Fuel to Generate Electricity

11.4 Fuel Cells Consume Fuel to Generate Electricity Hydrogen–Oxygen Fuel Cell Continuous supply of H2, H2O, and O2 Releases H2O as the product Anode reaction (oxidation) 2H2(g) + 4OH–(aq)  4H2O(g) + 4 e– Cathode reaction (reduction) 4 e– + O2(g) + 2H2O(g)  4OH–(aq)

11.4 Fuel Cells Consume Fuel to Generate Electricity H2 for fuel is not naturally abundant Requires large amount of energy to produce Produced by electrolysis of water From organic sources such as CH4, which also produces CO2 Requires large volumes for storage because it is a gas

11.4 Fuel Cells Consume Fuel to Generate Electricity Molten Carbonate Fuel Cell (MCFC) Suited for individual buildings, not entire regions

11.5 Photovoltaic Transform Light into Energy Photovoltaic Cells Most direct means of converting sunlight to electrical energy Used on satellites in the 1960s Can be installed on homes and at many other locations

11.5 Photovoltaic Transform Light into Energy

11.5 Photovoltaic Transform Light into Energy Photovoltaic cells are made of silicon doped to be n- and p-types n-type contains extra electrons p-type contains electron holes

11.5 Photovoltaic Transform Light into Energy Electrical energy is produced by joining the two types of silicon

11.5 Photovoltaic Transform Light into Energy Photoelectric Effect The ability of light to knock electrons away from atoms Creates a motion of electrons that can be directed and utilized

11.6 Electrolysis Produces Chemical Change The use of electrical energy to produce chemical change Can be used to break apart water, purify metals, and recharge car batteries

11.6 Electrolysis Produces Chemical Change Purification of aluminum metal by electrolysis Discovered by Hall and Heroult in 1886 Strong current is passed through mixture of Al2O3 and Na3AlF6 2AlOF32– + 6F– + C  2AlF63– + CO2 + 4e– AlF63– + 3e–  Al + 6F–

11.6 Electrolysis Produces Chemical Change

Concept Check Is the exothermic reaction in a hydrogen–oxygen fuel cell an example of electrolysis?

Concept Check No. During electrolysis, electrical energy is used to produce chemical change. In the hydrogen–oxygen fuel cell, chemical change is used to produce electrical energy.

11.7 Metal Compounds Can Be Converted to Metals Metal containing compounds can be converted to elemental metals utilizing oxidation-reduction reactions M+ + e–  M0 reduction Metals are difficult to reduce however

11.7 Metal Compounds Can Be Converted to Metals

Concept Check Why is it so difficult to obtain a group 1 metal from a compound containing ions of that metal?

Concept Check The metal ions do not readily accept electrons to form metal atoms.

11.7 Metal Compounds Can Be Converted to Metals Some metals are commonly obtained from metal oxides Blast furnaces can be used for the transformation Electrolysis is another method

11.7 Metal Compounds Can Be Converted to Metals

11.7 Metal Compounds Can Be Converted to Metals Small amount of C remaining strengthens the iron, which is called steel

11.7 Metal Compounds Can Be Converted to Metals High-purity copper is recovered by electrolysis

11.7 Metal Compounds Can Be Converted to Metals Other metals can be obtained from sulfides MS(s) + O2  M(l) + SO2(g) Commonly used to purify copper

11.8 Oxygen Is Responsible for Corrosion and Combustion Oxygen is able to pluck electrons from other elements Results in corrosion and combustion

11.8 Oxygen Is Responsible for Corrosion and Combustion Oxidation of a metal by oxygen Widespread and costly problem Billions of dollars a year are spent in the United States for steel alone 4Fe + 3O2 + 3H2O  2Fe2O3  3H2O

11.8 Oxygen Is Responsible for Corrosion and Combustion Other Type of Corrosion Aluminum oxidizes to Al2O3 and creates a protective coating over the metallic aluminum Zinc is used in galvanization as a sacrificial metal coating

11.8 Oxygen Is Responsible for Corrosion and Combustion Cathodic Protection Use of a more easily oxidized metal to protect a metallic structure

11.8 Oxygen Is Responsible for Corrosion and Combustion Rapid oxidation-reduction reaction between a material and oxygen Characteristically exothermic and often violent Oxidation of methane CH4 + 2O2  CO2 + 2H2O + energy