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Warmup

Warmup. What are the ionizations of the components of each of these molecules? Cu, CuSO 4 , Zn, ZnSO 4 What are the electronegativities of Cu and Zn? Categorize the reaction { endo , exo }, { synth decomp single double neut }: Zn + CuSO4  Cu + ZnSO4. Warmup.

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Warmup

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  1. Warmup What are the ionizations of the components of each of these molecules? Cu, CuSO4, Zn, ZnSO4 What are the electronegativities of Cu and Zn? Categorize the reaction {endo, exo}, {synthdecomp single double neut}: Zn + CuSO4  Cu + ZnSO4

  2. Warmup Zn + CuSO4 Cu + ZnSO4 Identify which element above is being oxidized, and which element is being reduced. Then write it as two separate equations, which may have ions and free electrons instead of neutral molecules.

  3. Warmup Calculate the electrochemical potential of the following electrode combinations, assuming an effective 1M (M  mol/L) electrolyte concentration. Li and Cl Pb and PbSO4 Al and Fe (II->0) Al and Fe (III->II) See p. 674, Table 21.2

  4. NOVEMBER 3, 2010 Electrochemical Reactions

  5. Whiteboard practice • Convert words to symbols, looking up polyatomc ions as needed • Find ionizations • Find molecular stochiometry • Balance the chemical equation • Categorize the chemical equation, if possible 1) Iron and hydrogen sulfate form iron (III) sulfate and molecular hydrogen gas. Things get warmer. 2) Silicon dioxide and hydrogen fluoride create silicon tetrafluoride and dihydrogen monoxide, which is hot afterwards. Molecular oxygen may be present as either a reactant or product.

  6. Whiteboard practice • Convert words to symbols, looking up polyatomc ions as needed • Find ionizations • Find molecular stochiometry • Balance the chemical equation • Categorize the chemical equation, if possible Arsenic is added to a sodium hydroxide solution, which creates hydrogen gas bubbles and sodium arsenate paste. Ammonium nitrate is cooked until it breaks down into molecular nitrogen, molecular oxygen, and dihydrogen monoxide. Oxygen may be present as either a reactant or product.

  7. Reduction-Oxidation Vocabulary When something is oxidized, it gives up electrons. When something is reduced, it gains electrons. Ex: Zn + O  ZnO Zinc loses two electrons and becomes a Zn+2 ion. It has been oxidized. Meanwhile, oxygen has been reduced. Oxidizers have high electronegativities. Reduction agents have low electronegativities.

  8. Anode and Cathode Anions make you cry (negative), but cats make you smile (positive). The site of oxidation is the anode where e- are produced, and is labeled negative. The site of reduction is the cathode where e- are absorbed, and is labeled positive. Ex: Overall reaction is: Zn + CuSO4  Cu + ZnSO4 Split into two sites: Zn  Zn+2 + 2e- Cu+2 + 2e-  Cu Sulfate ions are travelling from site 2 to site 1.

  9. Practice • Divide the reaction into two sites, and label them: • Cathode or anode • Oxidizing reaction or reducing reaction • Positive or negative side • Pb(s) + PbO2(s) + 2H2SO4(aq)  2PbSO4(s) + 2H2O(l) (Lead-acid battery) • 2H2 + O2  2H2O (Hydrogen Fuel Cell) • 2Zn + 2MnO2 + 2NH4Cl  Mn2O3 + 2NH3 + H20 + 2ZnCl (Dry Cell) • Zn + CuSO4  ZnSO4 + Cu

  10. Electrochemical Potentials See p. 674, Table 21.2

  11. Series vs. Parallel Batteries in series improves voltage. Batteries in parallel improves current output, and or longevity, as do larger surface areas of electrodes. Notation and equations:

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