1. Redox Reactions and Electrolysis
Chapter 7
Redox Reactions and Electrolysis

2. What is a Redox Reaction?
7.1
What is a Redox Reaction?

3. A. Oxidation and Reduction
Gain of oxygen
2Mg(s) + O2(g)  2MgO(s)
Mg has been oxidized
Loss of oxygen
CuO(s) + H2(g)  Cu(s) + H2O(l)
CuO has been reduced

4. B. Redox Reactions
Redox Reactions – oxidation-reduction reactions take place together

5. A. Oxidation and Reduction
Gain of oxygen
2Mg(s) + O2(g)  2MgO(s)
Mg has been oxidized
Removal of hydrogen from a compound (organic)
Loss of oxygen
CuO(s) + H2(g)  Cu(s) + H2O(l)
CuO has been reduced
Addition of hydrogen to a compound (organic)

6. Check-Up-#1- Pg. 107

8. Redox and Electron Transfer
7.2
Redox and Electron Transfer

9. Redox and Electron Transfer
We can define oxidation and reduction with respect to electron transfer and changes in oxidation number

10. Oxidation and Reduction
Gain of oxygen
2Mg(s) + O2(g)  2MgO(s)
Mg has been oxidized
Removal of hydrogen from a compound (organic)
Oxidation Is Loss of electrons (OIL)
Loss of oxygen
CuO(s) + H2(g)  Cu(s) + H2O(l)
CuO has been reduced
Addition of hydrogen to a compound (organic)
Reduction Is Gain (RIG)

11. A. Half-Equations
We can divide a reaction into two half equations – show separate oxidation-reduction reactions
2Na(s) + Cl2(g)  2NaCl(s)
Redox-Reaction Video

12. A. Half-Equations
We can divide a reaction into two half equations – show separate oxidation-reduction reactions
Fe(s) + Cu2+(aq) Fe2+(aq) + Cu(s)

13. B. Balancing Half-Equations
Use 2 half-reactions to write a balanced ionic equation - # electrons lost and gained in a redox reaction must be equal

14. Worked Example #1 – Pg. 108
Construct a balanced ionic equation for the reaction between nickel and iron (III) ions, from the half equations:
Ni(s) → Ni2+ (aq) + 2e-
Fe3+ (aq) + e- → Fe2+ (aq)
Ni(s) → Ni2+ (aq) + 2e-
2(Fe3+ (aq) + e- → Fe2+ (aq))
2Fe3+ (aq) + 2e- → 2Fe2+ (aq))
2Fe3+ (aq) + 2e- → 2Fe2+
Ni(s) + 2Fe3+ (aq) → Ni2+ (aq) + 2Fe2+

15. Worked Example #2 – Pg. 108

16. Check-Up-#2 – Pg. 109

17. 7.3
Oxidation Numbers

18. A. What are oxidation numbers?
Oxidation Number – number given to each atom or ion in a compound which shows us its degree of oxidation (represents the charge an atom would have if e- were transferred completely to the atoms with the greater attraction for them in a given situation)
+, -, 0
High (+) = more oxidized
High (-) = more reduced

19. B. Oxidation Number Rules

20. B. Oxidation Number Rules

21. C. Applying the Oxidation # Rules
Metal & Nonmetal

22. C. Applying the Oxidation # Rules
Nonmetal & Nonmetal – most electronegative element given negative sign

23. C. Applying the Oxidation # Rules
Compound Ions

24. Check-Up- #3 – Pg. 114

25. D. Redox and Oxidation Numbers
We can define oxidation and reduction in terms of oxidation # changes of particular atoms during a reaction

26. Oxidation and Reduction
Gain of oxygen
2Mg(s) + O2(g)  2MgO(s)
Mg has been oxidized
Removal of hydrogen from a compound (organic)
Oxidation Is Loss of electrons (OIL)
Increase in oxidation #
Loss of oxygen
CuO(s) + H2(g)  Cu(s) + H2O(l)
CuO has been reduced
Addition of hydrogen to a compound (organic)
Reduction Is Gain (RIG)
Decrease in oxidation #

27. D. Redox and Oxidation Numbers
Sn + 4HNO3  SnO2 + 4NO2 + 2H2O

28. D. Redox and Oxidation Numbers
Oxidizing Agent
Reducing Agent
Increases ox. # of another atom
Deceases in ox. #
Substance that gets reduced (gains e-)
Decreases ox. # of another atom
Increases in ox. #
Substance that gets oxidized (loses e-)

30. Check-Up - #4 – Pg. 114

31. E. Naming Compounds
Iron(II) Chloride
Iron(III) Chloride

32. E. Naming Compounds
Oxides of Nitrogen
N2O NO
NO2

33. E. Naming Compounds
Nitrate Ions
NaNO2
NaNO3

34. E. Naming Compounds Ions w/ Oxygen + 1 other element = end -ate
Cl + oxygen =
S + oxygen =

35. E. Naming Compounds Inorganic Acids w/ Oxygen = end in -ic H3PO3 =
HClO4 =

36. Check-Up - #5 – Pg. 116 Sodium sulfate (IV) Sodium sulfate (VI)
Iron(II) nitrate(V)
Iron(III) nitrate(V)
Iron(II) sulfate(VI)
Copper(I) oxide
Sulfuric(IV) acid
Manganese(VII) oxide

37. Worked Example - #3 – Pg. 117
Sodium Chlorate (V)

38. Check-Up - #6 – Pg. 117

39. F. Balancing Chemical Equations Using Ox. #
We can use ox. #s to balance equations involving redox reactions

40. Worked Example #4 – Pg. 117
Write a balanced chemical equation

41. Worked Example #5 – Pg. 117
Write a balanced chemical equation

42. Check-Up - #7 – Pg. 118

43. 7.4
Electrolysis

44. Electrolytic Cells
Electrolysis – decomposition of a compound into its elements by an electric current
Used to extract metals which ore are high in reactivity series
Used to produce non-metals such as chlorine and to purify some metals

46. Check-Up - #8 – Pg. 119

47. B. Redox Reactions in Electrolysis

49. Check-Up - #9 – Pg. 119

50. C. Extracting Aluminum 6O2-  3O2 + 12e-
O2 reacts w/ hot carbon electrodes
Oxidizes them to CO2 which escapes from cell
Electrodes must be replaced periodically
C. Extracting Aluminum
Al3+ + 3e-  Al
Reduced
Dense, sinks to bottom

51. C. Extracting Aluminum
Al2O3 molten via passing a high electric current through electrolyte (40,000 A)
However, Al2O3 has a high MP = lots of E needed = $$$
Energy needed is lowered by dissolving Al2O3 in large amounts of cryolite (Na3AlF6)
Lowers MP of Al2O3 to 970oC
Improves electrical conductivity of electrolyte

53. Check-Up - #7 – Pg. 120

54. D. Electrolysis of Brine
Concentrated aqueous solution of NaCl
Obtained from seat water or dissolving rock salt in H2O
Used to produce chlorine, hydrogen, and sodium hydroxide
Ions in brine: Na+, Cl-, H+ (from H2O), OH- (from H2O)

56. 2H+ + 2e-  H2
Na+
Cl-
2Cl-  Cl2 + 2e- H+
OH-

57. Check-Up - #11 – Pg. 122

58. E. The Electrolytic Purification of Copper
Copper  smelting in furnace (water pipes)
Not pure enough for electrical wiring because even small impurities reduce conductivity
Need 99.99% pure copper
Done through electrolysis

59. Anode decreases in thickness
Cu  Cu2+ + 2e-
Cu2+ + 2e-  Cu
Cu atoms deposited on cathode
Cu2+
Cathode increases in thickness
When “full,” cathode is removed and replaced

60. Check-Up - #12 – Pg. 123