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Oxidation/Reduction Reactions

Oxidation/Reduction Reactions. REDOX REACTONS!. All chemical reactions fall into two categories those that are redox and those that are not redox ! Redox reactions involve the transfer of electrons.

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Oxidation/Reduction Reactions

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  1. Oxidation/Reduction Reactions • REDOX REACTONS! • All chemical reactions fall into two categories those that are redox and those that are not redox! • Redox reactions involve the transfer of electrons. • 2Zn(s) + O2(g)  2ZnO(s) is an example of a redox reaction, watch the following video to see what happens to the Zn metal and the oxygen gas. • http://www.youtube.com/watch?v=e6Xxz-VBE6s • Remember that ZnO(s) is an ionic compound composed of Zn2+ and O2- ions.

  2. What is oxidation and reduction? • Oxidation • Early chemists thought of oxidation as the combining of an element with oxygen, as in combustion. • Now we refer to oxidation as the loss of electrons. • In the previous example Zn loses two electrons, Zn(s)  Zn2+ + 2e- • Reduction • Early chemists thought of reduction as the loss of oxygen from a compound. • Now we refer to reduction as the gain of electrons. • In the previous example O must gain the electrons that Zn loses, O + 2e- O2-

  3. Redox reactions without oxygen: • Mg(s) + S(s)  MgS(s) • This reaction can be broken down into two steps: • Mg  Mg2+ + 2e-(loss of electrons: oxidation) • S + 2e-  S2- (gain of electrons: reduction) • H2(g) + Cl2(g)  2HCl(g) • Hydrogen and chlorine undergo the following changes to form a hydrogen chloride molecule: • H  H+ + e- (loss of electrons: oxidation) • Cl + e-  Cl- (gain of electrons: reduction)

  4. “LEO the lion says GER” Elements can be oxidized or reduced depending on the reaction. Observe Iron in the following reactions: (remember that Iron III oxide is an ionic compound) • Oxidation • 4Fe(s) + 3O2(g)  2Fe2O3(s) - combustion or rusting • Fe  Fe3+ + 3e- - Loss of Electrons - Oxidation • Reduction • 2Fe2O3(s) + 3C(s)  4Fe(s) + 3CO2(g)-loss of oxygen • Fe3+ + 3e-  Fe -Gain of Electrons - Reduction

  5. Oxidation and Reduction must occur simultaneously: • If one element is oxidized then another must be reduced! • Example: 2AgNO3(aq) + Cu(s)  2Ag(s) + Cu(NO3)2(aq) • Net Ionic: 2Ag+ + Cu  2Ag + Cu2+ • Nitrates ions are spectator ions! • Half Reactions: • 2Ag+ + 2e- 2Ag Reduction • Cu  Cu2+ + 2e- Oxidation • These reactions occur simultaneously and the electrons lost must equal the electrons gained. • Remember that silver and copper II nitrate are soluble and hence are dissociated ions AgNO3(aq) is Ag+(aq) and NO3-(aq)

  6. When silver tarnishes it forms a black silver sulfide compound according to the following reaction: • 2Ag(s) + S(s)  Ag 2 S(s) • Observe the following video and write the oxidation and reduction half reactions: http://www.youtube.com/watch?v=a6RR4kPsnlE&feature=related • Ag  Ag+ + 1e- (oxidation) • S + 2e- S2- (reduction)

  7. Chapter 20.1- Read pages 631  638 • Complete question #1, #2 page 634 • Complete question #3  #8 page 638 • Complete Worksheet – Redox - 1

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