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CHEMISTRY CHAPTER 19

CHEMISTRY CHAPTER 19. Oxidation-Reduction Reactions. LEO SAYS GER. Oxidation and Reduction (Redox). Electrons are transferred. Spontaneous redox reactions can transfer energy Electrons (electricity) Heat. Non-spontaneous redox reactions can be induced with electricity.

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CHEMISTRY CHAPTER 19

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  1. CHEMISTRY CHAPTER 19 Oxidation-Reduction Reactions LEO SAYS GER

  2. Oxidation and Reduction (Redox) • Electrons are transferred • Spontaneous redox reactions can transfer energy • Electrons (electricity) • Heat • Non-spontaneous redox reactions can be induced with electricity

  3. Oxidation Reduction Reactions(Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:

  4. LEO says GER : LoseElectrons=Oxidation Sodium is oxidized GainElectrons=Reduction Chlorine is reduced

  5. OIL RIG : OxidationIsLoss Sodium is oxidized ReductionIs Gain Chlorine is reduced

  6. 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.

  7. Rules for Assigning Oxidation NumbersRules 3 & 4 3.The oxidation number of oxygen in compounds is -2 except in peroxide H2O2 4. The oxidation number of hydrogen in compounds is +1, except when combined with a metal (LiH)

  8. 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

  9. 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 + 4(-2) = -2 S O X + 3(-2) = -1 N O  X = +5  X = +6

  10. Pause for a CauseExercise on Assigning Oxidation Numbers • Assign oxidation numbers to each of the elements in the following compounds:

  11. Not All Reactions are Redox Reactions Reactions in which there has been no change in oxidation number are not redox reactions. Examples:

  12. Rules for Balancing Redox ReactionsRule 1 Assign oxidation numbers to atoms and determine those atoms that undergo changes in oxidation state (number). 0 +2 -1 +3 -1 0 Al + CuCl2 ------> AlCl3 + Cu Oxidized: Aluminum Reduced: Copper

  13. Rules for Balancing Redox ReactionsRule 2 2. Write the equation for oxidation and reduction. 0 +2 -1 +3 -1 0 Al + CuCl2 ------> AlCl3 + Cu 0 +3 Oxidation: Al  Al +2 0 Reduction: Cu  Cu

  14. Rules for Balancing Redox EquationsRule 3 3. Balance atomically. 0 +2 -1 +3 -1 0 Al + CuCl2 ------> AlCl3 + Cu 0 +3 Oxidation: Al  Al +2 0 Reduction: Cu  Cu • Al and Cu do not have subscripts so the equation is already balanced atomically. If a subscript was present, it would have been necessary to supply the proper coefficient.

  15. Rules for Balancing Redox EquationsRule 4 4. Balance electrically. 0 +2 -1 +3 -1 0 Al + CuCl2 ------> AlCl3 + Cu 0 +3 Oxidation: Al  Al + 3e- +2 0 Reduction: 2e- + Cu  Cu • The total charge on either side of the equation is now = to zero!

  16. Rule for Balancing Redox EquationsRule 5 5. Adjust coefficients in both equations so that the number of electrons lost = the number of electrons gained. 0 +2 -1 +3 -1 0 Al + CuCl2 ------> AlCl3 + Cu 0 +3 Oxidation:2 (Al  Al + 3e-) 2Al  2Al + 6e- +2 0 Reduction:(2e- + Cu  Cu) 3 6e- + 3 Cu 3Cu Six electrons will cancel six electrons!

  17. Rules for Balancing Redox EquationsRule 6 6. Place coefficients in skeletal equation 0 +2 -1 +3 -1 0 2 Al + 3 CuCl2 ------> 2 AlCl3 + 3 Cu

  18. Rules for Balancing Redox Equations Rule 7 7. Supply proper coefficients to the rest of the equation. 0 +2 -1 +3 -1 0 2 Al + 3 CuCl2 ------> 2 AlCl3 + 3 Cu All coefficients have been supplied in this equation. Use the trial and error procedure for balancing chemical equations to find unknown coefficient(s).

  19. Practice Redox Equation- Teacher Example H2C2O4 + K2Cr2O7 + H2SO4 KHSO4 + Cr2(SO4)3 + CO2 + H2O

  20. Practice Redox Equation- You Try! KMnO4 + HCl + H2S  KCl + MnCl2 + S + H2O

  21. Practice Redox Equation #1 HNO3 + S  NO2 + H2SO4 + H2O

  22. Practice Redox Equation #2 CrCl3 + MnO2 + H2O  MnCl2 + H2CrO4

  23. Practice Redox Equation #3 HNO3 + S  NO + H2SO4

  24. Practice Redox Equation #4 Na2TeO3 + NaI + HCl  NaCl + H2O + Te + I2

  25. Practice Redox Equation #5 KClO3 + Na2SnO2 KCl + Na2SnO3

  26. Practice Redox Equation #6 Bi(OH)3 + Na2SnO2 Na2SnO3 + H2O + Bi

  27. Practice Redox Equation #7 KClO3 + H2SO4 + FeSO4 Fe2(SO4)3 + KCl + H2O

  28. Practice Redox Equation #8 FeCl3 + SnCl2 FeCl2 + SnCl4

  29. Practice Redox Equation #9 KMnO4 + H2O2 + H2SO4 KHSO4 + MnSO4 + H2O + O2

  30. Practice Redox Equation #10 H2SO3 + HNO3 H2SO4 + H2O + NO

  31. Practice Redox Equation #11 Zn + NaOH + NaNO3 Na2ZnO2 + NH3 + H2O

  32. Practice Redox Equation #12 KMnO4 + FeSO4 + H2SO4 K2SO4 + MnSO4 + Fe2(SO4)3 + H2O

  33. Practice #13 KMnO4 + HCl + FeCl2 FeCl3 + MnCl2 + KCl + H2O

  34. Reducing Agents and Oxidizing Agents • The substance reduced is the oxidizingagent • The substance oxidized is the reducingagent Sodium is oxidized – it is the reducing agent Chlorine is reduced – it is the oxidizing agent

  35. 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

  36. Electrochemical Terminology Electrode: A conductor used to establish contact with a nonmetallic part of a circuit, such as an electrolyte Half-cell: a metal electrode in contact with a solution of its own ions Anode: The electrode where oxidation takes place Cathode: The electrode where reduction takes place

  37. Voltaic Cells Anode: negative Cathode: positive Voltaic cells: Electrochemical cells in which a spontaneous redox reaction can be harnessed to produce an electric current.

  38. Spontaneous Voltaic CellZinc – Copper Battery

  39. Electrolytic Cells Anode: positive Cathode: negative Electrolytic cells: Electrochemical cell in which an electric current is used to drive a non-spontaneous process

  40. Electrolysis of H2O 2H2O  2H2 + O2

  41. 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

  42. The End! The End! The End! The End! The End! The End! The End!

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