1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

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

8. Concept Check
Both statements are true.

9. 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

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

11. 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.

12. 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

13. 11.2 Harnessing the Energy of Flowing Electrons

14. 11.2 Harnessing the Energy of Flowing Electrons

15. 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

16. 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

17. 11.3 Batteries Consume Chemicals to Generate Electricity

18. 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 (–)

19. 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

20. 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)

21. 11.3 Batteries Consume Chemicals to Generate Electricity

22. 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)

23. 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

24. 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

25. 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

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

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

28. 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

29. 11.4 Fuel Cells Consume Fuel to Generate Electricity

30. 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)

31. 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

32. 11.4 Fuel Cells Consume Fuel to Generate Electricity
Molten Carbonate Fuel Cell (MCFC)
Suited for individual buildings, not entire regions

33. 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

34. 11.5 Photovoltaic Transform Light into Energy

35. 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

36. 11.5 Photovoltaic Transform Light into Energy
Electrical energy is produced by joining the two types of silicon

37. 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

38. 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

39. 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–

40. 11.6 Electrolysis Produces Chemical Change

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

42. 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.

43. 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

44. 11.7 Metal Compounds Can Be Converted to Metals

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

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

47. 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

48. 11.7 Metal Compounds Can Be Converted to Metals

49. 11.7 Metal Compounds Can Be Converted to Metals
Small amount of C remaining strengthens the iron, which is called steel

50. 11.7 Metal Compounds Can Be Converted to Metals
High-purity copper is recovered by electrolysis

51. 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

52. 11.8 Oxygen Is Responsible for Corrosion and Combustion
Oxygen is able to pluck electrons from other elements
Results in corrosion and combustion

53. 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

54. 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

55. 11.8 Oxygen Is Responsible for Corrosion and Combustion
Cathodic Protection
Use of a more easily oxidized metal to protect a metallic structure

56. 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