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Oxidation - Reduction Reactions

Oxidation - Reduction Reactions. a ka “Redox” corresponding to chapter 20 in text. Oxidation - Reduction reactions. Redox reactions involve Complete or partial transfer of electrons Change in oxidation numbers Oxidation numbers are pseudo charges. Rules for Oxidation Numbers.

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Oxidation - Reduction Reactions

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  1. Oxidation - Reduction Reactions aka “Redox” corresponding to chapter 20 in text

  2. Oxidation - Reduction reactions • Redox reactions involve • Complete or partial transfer of electrons • Change in oxidation numbers • Oxidation numbers are pseudo charges

  3. Rules for Oxidation Numbers • Usually is the charge the atom would have if it was an ion • Monatomic ion = ionic charge • H is always 1+ unless bound to metal (1-) • O is always 2- unless in peroxide (1-) • Free elements are always 0 (HONClBrIF too) • Σ of neutral compounds constituent oxidation numbers = 0 • Σ of polyatomic constituent oxidation numbers = charge

  4. Assigning Oxidation Numbers NaClO H2SO4 H2O NaCl NaCrO2 NaOH H2O2 Na2CrO4 OH-1 Ag HNO3 AgNO3 NO Ca(OH)2 Cl2 CaCl2 Ca(ClO3)2 KNO3

  5. LEO the lion says GER • Can’t have a growl without a lion • Can’t have oxidation without reduction • Paired reaction

  6. LEO the lion… • L = Lose • E = Electrons • O = Oxidation • Oxidation: Loss of electrons

  7. LEO the lion… • Fe+2 Fe+3 + e- • Oxidation number becomes more positive • Gained oxygen • Shifts electrons away

  8. …says GER • G = Gain • E = Electrons • R = Reduction • Reduction: Gain of electrons

  9. …says GER • Fe+3 + e-  Fe+2 • Oxidation number becomes more negative • Loss of oxygen • Shifts electrons towards

  10. Why do Lions Growl? • Oxidation and reduction occur together • Why? • Presence of oxidizingand reducing agents

  11. Agents • Oxidizing Agent • Substance that is being reduced • Hence, causing the oxidation • Reducing Agent • Substance that is being oxidized • Causing the reduction

  12. Balancing Redox Reactions • 2 methods • Half reaction • (preferred by chemists) • Oxidation number change • (preferred by lazy students and can lead you astray)

  13. Half Reaction (from book)

  14. Half Reaction (basics) • Separate the equation into the oxidation portion and the reduction portion • Balance both separately for e- gained or lost • Multiply each ½ rxn to yield a balanced overall e- shift • Put coefficients back up into the original eq • Balance “spectators” for atoms

  15. Try It! • Write the balanced redox reaction for the following: • Na(s) + FeCl2(aq)  NaCl(aq) + Fe(s)

  16. Oxidation Number Change Method • Step 1: assign oxidation numbers • Step 2: ID atoms being oxidized and reduced • Step 3: use brackets to connect the oxidation (loss of e-) and reduction (gain in e-)

  17. Same eq… but using ox number change method 0 +2-1 +1 -1 0 • Na(s) + FeCl2(aq)  NaCl(aq) + Fe(s)

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