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Oxidation & Reduction Reactions CHAPTER 6 Chemistry: The Molecular Nature of Matter, 6 th edition

Oxidation & Reduction Reactions CHAPTER 6 Chemistry: The Molecular Nature of Matter, 6 th edition By Jesperson , Brady, & Hyslop. CHAPTER 6: Oxidation & Reduction. Learning Objectives Define oxidation and reduction Identify redox reactions Recognize oxidation numbers

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Oxidation & Reduction Reactions CHAPTER 6 Chemistry: The Molecular Nature of Matter, 6 th edition

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  1. Oxidation & Reduction Reactions CHAPTER 6 Chemistry: The Molecular Nature of Matter, 6th edition By Jesperson, Brady, & Hyslop

  2. CHAPTER 6: Oxidation & Reduction • Learning Objectives • Define oxidation and reduction • Identify redox reactions • Recognize oxidation numbers • Balancing redox reactions • Acidic conditions • Basic conditions • Acids as oxidizing agents • Oxygen as oxidizing agents • Single replacement reactions • Navigate the activity series • Practice Redox Stoichiometry

  3. Reduction Oxidation Acids as Oxidizing Agents • Metals often react with acid • Form metal ions and • Molecular hydrogen gas Molecular equation Zn(s) + 2HCl(aq) H2(g) + ZnCl2(aq) Net ionic equation Zn(s) + 2H+(aq) H2(g) + Zn2+(aq) • Zn is oxidized • H+is reduced • H+is the oxidizing reagent • Zn is the reducing reagent Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  4. Reduction Oxidation Acids as Oxidizing Agents: Metals • Ease of oxidation process depends on metal • Metals that react with HCl or H2SO4 • Easily oxidized by H+ • More active than hydrogen (H2) e.g.Mg, Zn, alkali metals Mg(s) + 2H+(aq)  Mg2+(aq) + H2(g) 2Na(s) + 2H+(aq)  2Na+(aq) + H2(g) • Metals that don’t react with HCl or H2SO4 • Not oxidized by H+ • Less active than H2 e.g.Cu, Pt Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  5. Reduction Oxidation Acids as Oxidizing Agents: Anions Determine Oxidizing Power Acids are divided into two classes: Nonoxidizing Acids • Anion is weaker oxidizing agent than H3O+ • Only redox reaction is • 2H+ + 2e– H2 or • 2H3O+ + 2e– H2 + 2H2O • HCl(aq), HBr(aq), HI(aq) • H3PO4(aq) • Cold, dilute H2SO4(aq) • Most organic acids (e.g., HC2H3O2) Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  6. Reduction Oxidation Acids as Oxidizing Agents • Anion is stronger oxidizing agent than H3O+ • Used to react metals that are less active than H2 • No H2 gas formed • HNO3(aq) • Concentrated • Dilute • Very dilute, with strong reducing agent • H2SO4(aq) • Hot, conc’d, with strong reducing agent • Hot, concentrated Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  7. Reduction Oxidation Acids as Oxidizing Agents: Focus on Nitrate Ion oxidation Concentrated HNO3 • NO3– more powerful oxidizing agent than H+ • NO2is product • Partial reduction of N (+5 to +4) • NO3–(aq) + 2H+(aq) + e–NO2(g) + H2O reduction 0 +5+2+4 Cu(s) + 2NO3–(aq) + 4H+(aq) Cu2+(aq) + 2NO2(g) + 2H2O Reducing agent Oxidizing agent Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  8. Reduction Oxidation Acids as Oxidizing Agents: Focus on Nitrate Ion Dilute HNO3 • NO3– is more powerful oxidizing agent than H+ • NOis product • Partial reduction of N (+5 to +2) • NO3–(aq) + 4H+(aq) + 3e –NO(g)+ 2H2O • Used to react metals that are less active than H2 Reaction of copper with dilute nitric acid 3Cu(s) + 8HNO3(dil, aq)  3Cu(NO3)2(aq) + 2NO(g) + 4H2O Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  9. Reduction Oxidation Acids as Oxidizing Agents: Focus on Sulfuric Acid Hot, Concentrated H2SO4 • Becomes potent oxidizer • SO2 is product • Partial reduction of S (+6 to +4) • SO42– + 4H++ 2e–SO2(g) + 2H2O Ex: Cu + 2H2SO4(hot, conc.) CuSO4 + SO2 + 2H2O Hot, concentrated with strong reducing agent • H2S is product • Complete reduction of S (+6 to –2) • SO42– + 10H+ + 8e–H2S(g)+ 4H2O Ex: 4Zn + 5H2SO4(hot, conc.)  4ZnSO4 + H2S + 4H2O Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  10. Reduction Oxidation Single Replacement Reaction Acids reacting with metal • Special case of more general phenomena: Single Replacement Reaction • Reaction where one element replaces another • A + BC→ AC + B • Metal A can replace metal B • If A is moreactivemetal, or • Nonmetal A can replace nonmetal C • If A is more active than C Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  11. Reduction Oxidation Single Replacement Reaction • Left = Zn(s) + CuSO4(aq) • Center = Cu2+(aq) reduced to Cu(s) Zn(s) oxidized to Zn2+(aq) • Right = Cu(s) plated out on Zn bar Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s) Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  12. Reduction Oxidation Single Replacement Reaction • Zn2+ ions take place of Cu2+ ions in solution • Cu atoms take place of Zn atoms in solid • Cu2+oxidizes Zn0 to Zn2+ • Zn0 reduces Cu2+ to Cu0 • More active Zn0 replaces less active Cu2+ • Zn0 is easier to oxidize! Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  13. Reduction Oxidation Activity Series of Metals • Cu less active, can't replace Zn2+ • Can't reduce Zn2+ • Cu(s) + Zn2+(aq)  No reaction • General phenomenon • Metal that is more easily oxidized will displace one that is less easily oxidized from its compounds Activity Series (Table 6.3) • Metals at bottom more easily oxidized (more active) than those at top • This means that given metal ion will be displaced from its compounds by any metal below it in table Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  14. Reduction Oxidation Activity Series of Metals 2H+(aq) + Sr(s)  Sr2+(aq) + H2(g) • H+ oxidizes Sr0 to Sr2+ • Sr0 reduces H+ to H2 • More active Sr0 replaces less active H+ • Sr0 is easier to oxidize! H2(g) + Sr2+(aq)  NO REACTION! • Why? • H2 less active, can't replace Sr2+ • Can't reduce Sr2+ Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  15. Reduction Oxidation Activity Series of Metals Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  16. Reduction Oxidation Activity Series of Metals • Metals at very bottom of table • Very strong reducing agents • Very easily oxidized • Na down to Cs • Alkali and alkaline earth metals • React with H2O as well as H+ 2Na(s) + 2H2O  H2(g) + 2NaOH(aq) Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  17. Reduction Oxidation Activity Series of Metals • Ag – slight reaction (top of activity series) • 2HCl(aq) + Ag(s)  2AgCl(aq) + H2(g) • Zn – somewhat reactive (middle of activity series) • 2HCl(aq) + Zn(s)  ZnCl2(aq) + H2(g) • Mg – very reactive (bottom of activity series) • 2HCl(aq) + Mg(s)  MgCl2(aq) + H2(g) Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  18. Reduction Oxidation Activity Series of Metals: Predicting Reactions If M is below H • Can displace H from solutions containing H+ 2H+(aq)  H2(g) If M is above H • Doesn't react with nonoxidizing acids • HCl, H3PO4, etc. In general • Metal below replaces ion above Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  19. Reduction Oxidation Activity Series of Metals: Predicting Reactions • Predictive tool for determining outcome of single replacement reactions • Given a metal (M ) and the ion of a different metal (M 'n+) • Look at chart and draw arrow from M to M 'n+ • Arrow that points up from bottom left to top right willoccur • Arrow that points down from top left to bottom right will NOT occur Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  20. Reduction Oxidation Oxygen as an Oxidizing Agent: Combustion Oxygen reacts with many substances Combustion • Rapid reaction of substance with oxygen that gives off both heat and light • Hydrocarbons are important fuels • Products depend on how much O2 is available 1. Complete Combustion • O2 plentiful • CO2 and H2O products e.g. CH4(g) + 2O2(g)  CO2(g) + 2H2O 2C8H18(g) + 25O2(g)  16CO2(g) + 18H2O Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  21. Reduction Oxidation Oxygen as an Oxidizing Agent: Combustion 2. Incomplete Combustion • Not enough O2 a.Limited O2 supply • CO(g) is the carbon product 2CH4(g) + 3O2(g)  2CO(g) + 4H2O b. Very limited O2 • C(s)is the carbon product CH4(g) + O2(g)  C(s) + 2H2O • Gives tiny black particles • Soot—lamp black • Component of air pollution Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  22. Reduction Oxidation Oxygen as an Oxidizing Agent: Combustion 3. Combustion of Organics containing O • Still produce CO2 and H2O • Need less added O2 C12H22O11(s) + 12O2(g)  12CO2(g) + 11H2O 4.Combustion of Organics containing S • Produce SO2as product 2C4H9SH + 15O2(g)  8CO2(g) + 10H2O + 2SO2(g) • SO2 turns into acid rain when mixed with water • SO2 oxidized to SO3 • SO3 reacts with H2O to form H2SO4 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  23. Reduction Oxidation Oxygen as an Oxidizing Agent: Corrosion Corrosion • Direct reaction of metals with O2 • Many metals corrodeor tarnish when exposed to O2 Ex. 2Mg(s)+ O2(g)  2MgO(s) 4Al(s) + 3O2(g)  2Al2O3(s) 4Fe(s) + 3O2(g)  2Fe2O3(s) 4Ag(s) + O2(g)  2Ag2O(s) Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  24. Reduction Oxidation Oxygen as an Oxidizing Agent: Reacting with Nonmetals • Many nonmetals react directly with O2 to form nonmetal oxides • Sulfur reacts with O2 • Forms SO2 S(s) + O2(g)  2SO2(g) • Nitrogen reacts with O2 • Forms various oxides • NO, NO2, N2O, N2O3, N2O4, and N2O5 • Dinitrogen oxide, N2O • Laughing gas used by dentists • Propellant in canned whipped cream Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  25. Reduction Oxidation Example of Redox Stoichiometry Same as other stoichiometry problems, except balancing the equation is more complicated. Ex.How many grams of Na2SO3 (126.1 g/mol) are needed to completely react with 12.4 g of K2Cr2O7 (294.2 g/mol)? • First need balanced redox equation 8H+(aq) + Cr2O72–(aq) + 3SO32–(aq)  3SO42–(aq) + 2Cr3+(aq) + 4H2O • Then do calculations 1. g K2Cr2O7 moles K2Cr2O7 moles Cr2O72–(aq) 2. moles Cr2O72–(aq)  moles 3SO42–(aq) 3. moles SO32–(aq)  moles Na2SO3 g Na2SO3 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

  26. Reduction Oxidation Example of Redox Stoichiometry grams K2Cr2O7 moles K2Cr2O7 moles Cr2O72–(aq) moles Cr2O72–(aq)  moles 3SO32–(aq) moles SO32–(aq)  moles Na2SO3 g Na2SO3 Jesperson, Brady, Hyslop. Chemistry: The Molecular Nature of Matter, 6E

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