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Redox Reactions

Redox Reactions. 13.1a Electron Transfer Theory. Overview. oxidation and reduction rxtns always occur together (redox rxtn) you can’t have one without the other examples extracting metal from an ore electroplating of metals salt on roads (corrosion)

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Redox Reactions

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  1. Redox Reactions 13.1a Electron Transfer Theory

  2. Overview • oxidation and reduction rxtns always occur together (redox rxtn) • you can’t have one without the other • examples • extracting metal from an ore • electroplating of metals • salt on roads (corrosion) • salt accelerates the reaction between oxygen and metal • makes electron transfer easier

  3. 3 perspectives of oxidation/reduction • 1) oxygen • oxidation gains and reduction loses • 2) hydrogen • oxidation loses and reduction gains • 3) electrons (modern view) • oxidation loses and reduction gains • most fundamental explanation, what we will be working with the most

  4. Sample Rxtn. We convert iron ore to metallic iron using carbon. What is being oxidized? 2Fe2O3 + 3C  4Fe + 3CO2 • we removed oxygen from the iron(III)oxide and the carbon gained oxygen • carbon was oxidized because it gained an oxygen

  5. Sample Rxtns. con’t Fe2O3 (s)+ 3 CO(g)2 Fe (s)+ 3CO2 (g) SnO2(s)+ C(s)Sn(s)+ CO2 (g) CuS(s)+ H2(g)Cu(s)+ H2S(g)

  6. Oxygen Hydrogen e-

  7. Redox with Electrons • many reactions may not even involve oxygen • redox currently refers to electrons being transferred between reactants • Mg + S Mg2+ + S2- (MgS) • the magnesium atom (which has zero charge) changes to a magnesium ion by losing 2 electrons, and is oxidized to Mg2+ • the sulfur atom (which has no charge) is changed to a sulfide ion by gaining 2 electrons, and is reduced to S2- • Mg is the reducing agent and S is the oxidizing agent • agents cause the other half of the rxtn. to occur

  8. Examples • Is the reactant oxidized or reduced? • Pb  PbO3 oxidized • SnO2  SnO reduced • KClO3 KCl reduced • C2H6O  C2H4O oxidized • C2H2  C2H6 reduced

  9. Homework Textbook p. 559 #1-4

  10. Redox Reactions 13.1a1 Electron Transfer Theory

  11. Leo the Lion! • LEO the lion says GER • Loss of electrons is oxidation, gain of electrons is reduction

  12. LEO says GER Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced

  13. LEO says GER con’t - losing electrons is oxidation, and the substance that loses the electrons is called the reducing agent. - gaining electrons is reduction, and the substance that gains the electrons is called the oxidizing agent. Mg(s) + S(s) MgS(s) Mg is oxidized: loses e-, becomes a Mg2+ ion Mg is the reducing agent S is the oxidizing agent S is reduced: gains e- = S2- ion

  14. Oxidizing and Reducing Agents CuO + H2 Cu + H2O • Cu goes from 2+ to 0 • Cu is reduced, therefore it is called an oxidizing agent because it causes some other substance to be oxidized • H goes from 0 to 1+ • H is oxidized, therefore it is called a reducing agent because it causes some other substance to be reduced

  15. Identifying Agents in an Equation • CuO + H2 Cu + H2O Reduction: CuO is the oxidizing agent Oxidation: H2 is the reducing agent

  16. Examples • A) H2(g) + Cl2 (g) 2HCl(g) • H2 oxidized Cl2 reduced • B) S(s) + Cl2 (g) SCl2(g) • S oxidized Cl2 reduced • C) N2 + 2O2 2NO2 • N2 oxidized O2 reduced • D) 2Li + F2 2LiF • Li oxidized F2 reduced • E) H2 + S H2S • H2 oxidized Sreduced

  17. Half-Cell Reactions The overall reaction: 2Fe + 3Cl2 2Fe3+ + 6Cl- may be written as the sum of two half-cell reactions: 2Fe  2Fe3+ + 6e- (oxidation) 3Cl2+ 6e- 6Cl- (reduction) Complete redox reactions can be expressed as the sum of two half reactions, one reduction and one oxidation.

  18. Homework Textbook p.564 #7-11 LSM 13.1B,C summary

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