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REDOX

Oxidation-Reduction Reactions. REDOX. Oxidation-Reduction Reactions. Electrons transferred 1 atom to another Examples of Redox reactions: All single-replacement rxns All combustion rxns. LEO GOES GER!!!. Oxidation is the loss of electrons L OSS of

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REDOX

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  1. Oxidation-Reduction Reactions REDOX

  2. Oxidation-Reduction Reactions • Electrons transferred 1 atom to another • Examples of Redox reactions: • All single-replacement rxns • All combustion rxns

  3. LEO GOES GER!!!

  4. Oxidation is the loss of electrons LOSS of ELECTRONS OXIDATION LEO

  5. Reduction is the gain of electrons GAIN of ELECTRONS REDUCTION GER

  6. REDOX • Oxidation & Reduction: complementary reactions • occur together & simultaneously or not at all

  7. Oxidation Numbers • In Ionic Compounds: • # of electrons lost/gained by atom determined by ions that form compound

  8. Assigning Oxidation Numbers

  9. Na He O2 N2 S8 Cl2 P Rule #1: ox # of free, uncombined element = 0

  10. Rule # 2: ox # of monatomic ion = charge of ion Ca+2 = +2 Cl-1 = -1 Al+3 = +3 Remember: Ions form ionic cmpds: CaCl2, Al(NO3)3, etc.

  11. Rule # 3: F always -1 CF4

  12. Rule # 4: H is nearly always +1 • except if bonded to metal then -1 H2O, HNO3, H2SO4, LiH, CaH2, NaH

  13. Rule # 5: OF2 - Bonded to F: O is +2 O22- • Bonded to peroxide ion: O is -1 • (group 1 & 2 metals) O is nearly always -2 except when:

  14. H2O CO2 NO SO3 Rule # 6 Sum ox # in neutral compound = 0

  15. Rule # 7 Sum ox # in polyatomic ion = charge of ion Sum in SO4-2 = -2 Sum in NO3-1 = -1

  16. Rule # 8 Covalent cmpds: ox # more electroneg atom isnegative *NH3: N = -3, H = +1 SiCl4: Si = +4, Cl = -1

  17. K = +1, Cl = -1 Al = +3, O = -2, N = +5 Assign Oxidation Nos • KCl • CaBr2 • CO • CO2 • Al(NO3)3 • Na3PO4 • H2S • NH4+1 • SO3-2 Ca = +2, Br = -1 C = +2, O = -2 C = +4, O = -2 Na = +1, O = -2, P = +5 H = +1, S = -2 N = -3, H = +1 S = +4, O = -2

  18. 4 3 2 1 0 -1 -2 -3 -4 2) if you’re lucky you strike oil & it shoots up 1) You dig down with an oil rig

  19. Electrons are Negative! • Why use the word “reduced” when electrons are gained? Look at how the oxidation number changes Ex: Cl gains an electron → Cl-1 • oxidation # ↓ from 0 to -1 so the # was reduced

  20. Writing Equations • Even though oxidation & reduction reactions occur together we write separate equations for each process • known as Half-Reactions

  21. Reduction Half-Reactions • I2 + 2e- 2I-1 • O2 + 4e- 2O-2 • Half-reactions must demonstrate: • conservation of mass & conservation of charge • # atoms on left must =# atoms on right • total charge on left must = total charge on right Electrons are gained so put on reactant side!

  22. Oxidation Half-reactions Electrons are lost so they are put on product side! • K  K1+ + 1e- • Fe2+ Fe3+ + 1e- • Cu  Cu2+ + 2e- • Total Charge on left =Total Charge onright • # atoms on left = # atoms on right

  23. Vocabulary Interlude • Oxidizing Agent: substance being reduced • accepts electrons from something else • aids oxidation for another species • Reducing Agent: substance being oxidized • loses electrons to something else • aids reduction for another species

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