1. Oxidation-Reduction Reactions REDOX Reactions

2. Oxidation State Oxidation numbers are very similar to charge. There are some different rules for assigning them.

3. Rules for Oxidation State 1. The oxidation number for any uncombined element is zero Ex. The oxidation state for Na is zero.

4. Rule 2 The oxidation number for a monatomic ion equals the charge on the ion. Ex. Cl -1 has an oxidation of -1.

5. Rule 3 The more electronegative element in a binary compound is assigned the number equal to the charge it would have if it were an ion. Ex. The oxidation number of O in NO is -2 because oxygen is more electronegative than nitrogen.

6. Rule 4 The oxidation number of fluorine in a compound is always -1. Ex. The oxidation number of F in LiF is -1.

7. Rule 5 Oxygen has an oxidation number of -2 unless it is combined with fluorine, when it is +2, or it is in a peroxide such as H 2 O 2, when it is - 1. Ex. The oxidation of O in NO 2 is -2.

8. Rule 6 The oxidation state of hydrogen in most of its compounds is +1 unless it is combined with a metal, in which case it is -1. Ex. The oxidation of H in LiH is -1. The oxidation of H in HCl is +1.

9. Rule 7 In compounds, Group 1 and 2 elements and aluminum have oxidation numbers of +1, +2, and +3, respectively. Ex. The oxidation number of Ca in CaCO 3 is +2.

10. Rule 8 The sum of the oxidation numbers of all atoms in a neutral compound is 0. Ex. The oxidation number of each atom in CaCO 3 can be found by knowing the rules above and knowing the compound is neutral Ca = +2 (rule 7) O = -2 x 3 atoms = -6 (rule 5) C = +4 (rule 8—balances out the charge)

11. Rule 9 The sum of the oxidation numbers of all atoms in a polyatomic ion equals the charge of the ion. Ex. The oxidation of each element in H 2 PO 4 2- can be determined by knowing the overall charge is -2 H = +1 x 2 atoms = +2 (rule 6) O = -2 x 4 atoms = -8 (rule 5) P = +4 (rule 9)

12. Types of Reactions 5 types plus a new one

13. Type of Reactions Chemical reactions are classified into five general types Combination Decomposition Single Replacement Double Replacement Combustion

14. Combination (Synthesis) Two or more elements or simple compounds combine to form (synthesize) one product A + B AB 2Mg + O 2  2MgO 2Na + Cl 2  2NaCl SO 3 + H 2 O  H 2 SO 4

15. Decomposition One substance is broken down (split) into two or more simpler substances. AB  A + B 2HgO  2Hg + O 2 2KClO 3  2KCl + 3 O 2

16. Learning Check R1 Classify the following reactions as 1) combination or 2) decomposition: ___A. H 2 + Br 2  2HBr ___B. Al 2 (CO 3 ) 3  Al 2 O 3 + 3CO 2 ___C. 4 Al + 3C  Al 4 C 3

17. Solution R1 Classify the following reactions as 1) combination or 2) decomposition: _1_A. H 2 + Br 2  2HBr _2_B. Al 2 (CO 3 ) 3  Al 2 O 3 + 3CO 2 _1_C. 4 Al + 3C  Al 4 C 3

18. Single Replacement One element takes the place of an element in a reacting compound. A + BC  AB + C Zn + 2HCl  ZnCl 2 + H 2 Fe +CuSO 4  FeSO 4 +Cu

19. Learning Check R2 Classify the following reactions as 1) single replacement 2) double replacement __ A. 2Al + 3H 2 SO 4  Al 2 (SO 4 ) 3 + 3H 2 __B. Na 2 SO 4 + 2AgNO  Ag 2 SO 4 + 2NaNO 3 __C. 3C + Fe 2 O 3  2Fe + 3CO

20. Solution R2 Classify the following reactions as 1) single replacement 2) double replacement 1_ A. 2Al + 3H 2 SO 4  Al 2 (SO 4 ) 3 + 3H 2 2_B. Na 2 SO 4 + 2AgNO 3  Ag 2 SO 4 + 2NaNO 3 1_C. 3C + Fe  2Fe + 3CO

21. Combustion A reaction in which a compound (often carbon) reacts with oxygen C + O 2  CO 2 CH 4 + 2O 2  CO 2 + 2H 2 O C 3 H 8 + 5O 2  3CO 2 + 4H 2 O C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O

22. Learning Check R3 Balance the combustion equation ___C 5 H 12 + ___O 2 ___CO 2 + ___H 2 O

23. Solution R3 Balance the combustion equation 1 C 5 H 12 + 8 O 2 5 CO 2 + 6 H 2 O

24. Oxidation-Reduction Reactions REDOX Rxns

25. Oxidation and Reduction  Reactions that involve a loss or gain of electrons  Occurs in many of the 4 types of reactions and combustion  Important in food metabolism, batteries, rusting of metals

26. Requirements for Oxidization-Reduction Electrons are transferred Two processes occur Oxidation = Loss of electrons (LEO) ZnZn 2+ + 2e - Reduction = Gain of electrons (GER) Cu 2+ + 2e - Cu

27. Balanced Red-Ox Equations Combine the oxidation and reduction reactions to make Loss of electrons = Gain of electrons Zn + Cu 2+ + 2e - Zn 2+ + 2e - + Cu Zn + Cu 2+ Zn 2+ + Cu

28. Gain/Loss of Hydrogen In organic and biological reactions oxidation = Loss of H reduction = Gain of H

29. Half-Reaction The part of a reaction involving oxidation or reduction alone. The overall reaction is the sum of the two half reactions Ex. 3Cu  3Cu 2+ + 6 e- 2NO 3 -1 + 6 e- + 8H +  2NO + 4 H 2 O 3Cu + 2NO 3 -1 + 8 H +  3Cu 2+ + 2NO + 4H 2 O

30. Learning Check R3 Identify the following as an 1) oxidation or a reduction process: __A. SnSn 4+ + 4e- __B. Fe 3+ + 1e - Fe 2+ __C. Cl 2 + 2e - 2Cl -

31. Solution R3 Identify the following as an 1) oxidation or a reduction process: 1_ A. SnSn 4+ + 4e- 2_ B. Fe 3+ + 1e - Fe 2+ 2_ C. Cl 2 + 2e - 2Cl -

32. Learning Check R4 In light-sensitive sunglasses, UV light initiates an oxidation- reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is oxidized 1) Ag + 2) Cl - 3) Ag B. Which reactant is reduced? 1) Ag + 2) Cl - 3) Cl

33. Solution R4 In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is oxidized 2) Cl - Cl - Cl + e - B. Which reactant is reduced? 1) Ag + Ag + + e- Ag

34. Oxidizing and Reducing Agents

35. Reducing Agents A substance that has the potential to cause another substance to be reduced. Lose electrons (gain higher charge)

36. Oxidizing Agent Substance that has the potential to cause another substance to be oxidized Gains electrons (become more negative)

37. Summary Chart of Terminology TermChange in oxidation number Change in electron population OxidationIncreasesLoss of electrons ReductionDecreasesGain of electrons Oxidizing agent DecreasesGains electrons Reducing agent IncreasesLoses electrons

38. Autooxidation A process in which a substance acts as both an oxidizing agent and a reducing agent

39. Electrochemistry Electrodes, half cells, anodes, cathodes, voltaic and electrolytic cells

40. Electrochemistry The branch of chemistry that deals with electricity-related applications of oxidation-reduction

41. A bright idea! As redox rxns occur, electrons are transferred which also produces heat. But if the substances are separated by a porous barrier then they are able to transfer electricity instead of heat

42. Electrode Conductor used to establish electrical contact with a nonmetallic part of a circuit such as an electrolyte

43. Half-cell A single electrode immersed in a solution of its ions.

44. Anode One half cell is the anode which is the electrode where oxidation takes place.

45. Cathode Other half cell where reduction takes place.

46. Electrochemical cell A system of electrodes and electrolytes in which either chemical reactions produce electrical energy of an electric current produces chemical change.

47. Voltaic Cells If the redox rxn in an electrochemical cell occurs spontaneously and produces electrical energy then it is a voltaic cell.

48. Types of Dry Cell Batteries Zinc-Carbon Dry Cells Alkaline Batteries Mercury batteries

49. Zinc-Carbon Dry Cells Ex. Flashlight batteries Have Zn container which is the anode Filled with moist paste of MnO 2, graphite, and NH 4 Cl

50. Alkaline Batteries Ex. Batteries found in small, portable devices such as CD players Very similar to the Zn-C but it does not contain the C which allows them to be smaller Uses paste of Zn and KOH instead of a solid metal anode.

51. Mercury Batteries Ex. Calculator batteries The anode half rxn is the same as the alkaline but the cathode involves HgO

52. Rechargeable cells Combination of voltaic and electrolytic cells Acts as a voltaic cell during use and as an electrolytic cell during charging. Ex. Car battery