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Ch.19 Redox Rxns

Ch.19 Redox Rxns. Glow Sticks!! Bioluminescence. Oxidation-Reduction Rxns (Redox Rxns) Transfer Electrons. Complete Chemical Equation: 2KBr (aq) + Cl 2(aq)  2KCl (aq) + Br 2(aq) Net Ionic Equation: 2Br - (aq) + Cl 2(aq)  Br 2(aq) + 2Cl - (aq). How To Write Net Ionic Equations.

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Ch.19 Redox Rxns

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  1. Ch.19 Redox Rxns

  2. Glow Sticks!! Bioluminescence

  3. Oxidation-Reduction Rxns (Redox Rxns) Transfer Electrons • Complete Chemical Equation: • 2KBr(aq) + Cl2(aq) 2KCl(aq) + Br2(aq) • Net Ionic Equation: • 2Br-(aq) + Cl2(aq) Br2(aq) + 2Cl-(aq)

  4. How To Write Net Ionic Equations • Net ionic equations show details of rxns involving ions in aqueous solutions. • If a substance is an ion in solution, it’s written as an ion in the equation. If it’s insoluble, it is written as a compound. • Ex. 2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s) • STEP 1: Write the complete ionic equation. • 2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq)  2Na+ (aq) + 2Cl-(aq) + Cu(OH)2(s)

  5. 2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq)  2Na+(aq) + 2Cl-(aq) + Cu(OH)2(s) • STEP 2: If the same ion is in both the reactant and the product sides of the equation, it does not participate in the reaction and is NOT written in the net ionic equation. It is a SPECTATOR ION. • 2OH-(aq) + Cu2+(aq)  Cu(OH)2(s)

  6. Examples Ba(NO3)2(aq) + Na2CO3(aq) BaCO3(s) + 2NaNO3(aq) • Ba2+(aq) + CO32-(aq)  BaCO3(s) • HBr(aq) + NaOH(aq)  H2O(l) + NaBr(aq) • H+(aq) + OH-(aq) H2O(l)

  7. Oxidation & Reduction2Na + Cl2 2NaCl • Oxidation: the loss of electrons from atoms of a substance. • Ex. Na  Na+ + e- • Electrons lost by the oxidized substance must be accepted by atoms or ions of another substance. • Reduction: the gain of electrons by atoms of a substance. • Ex. Cl2 + 2e- 2Cl- • Redox rxns are complementary! • LEO the lion says GER • (Loss of Electrons is Oxidation, Gain of Electrons is Reduction)

  8. Oxidation Number: # e-’s lost or gained when an atom forms ions. • When atoms are reduced, they gain e-’s and become negative. • When atoms are oxidized, they lose e-’s and become positive. • Ex. Cl is reduced to Cl-, K is oxidized to K+ • Ca? • Oxidized to Ca2+ • O? • Reduced to O2-

  9. Oxidizing & Reducing Agents • Oxidizing Agents: accept e-’s & are reduced in the process. • Reducing Agents: Lose e-’s & are oxidized in the process. • Ex. 2K + Cl2 2K+ + 2Cl- • What is oxidized? Reduced? • K is oxidized, Cl2 is reduced

  10. Summary of Redox Rxns

  11. Redox & Electronegativity • How do we know which atom is oxidized or reduced for a molecule? • ELECTRONEGATIVITY! • Low electronegativity = strong reducing agents • High electronegativity = strong oxidizing agents

  12. Determining Oxidation Numbers

  13. Determining Oxidation Numbers

  14. Oxidation Numbers in Redox Rxns

  15. Balancing Redox Equations • Redox equations are balanced when oxidation numbers increased = oxidation numbers decreased.

  16. Balancing Redox Equations Using Half-Rxns • Half Rxns: show either oxidation or reduction • 2Fe + 3Cl2 2FeCl3 • Oxidation: Fe  Fe3+ + 3e- • Fe loses 3e- • Reduction: Cl2 + 2e-  2Cl- • Cl accepts 2e-

  17. Half-Rxn Method StepsFe(s) + CuSO4(aq)  Cu(s) + Fe2(SO4)3(aq)

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