CHM1311 - Lecture(14)

CHM1311 - Lecture(14) - Electrochemistry (Redox Chemistry)...

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1 Electrochemistry Electrochemistry (Redox Chemistry) (Redox Chemistry) Petrucci, Chapter 21 Petrucci, Chapter 21
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2 ELECTROPLATING ELECTROPLATING PRODUCTION OF METALS PRODUCTION OF METALS RUST RUST BATTERIES BATTERIES Redox reactions have a broad range of applications Redox reactions have a broad range of applications Why study redox reactions?
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3 Graphite rods are used for the anode. These are consumed as the reaction progresses. Insoluble molten metallic aluminum falls to the bottom of the reactor, where it can be drawn off by a tap. The Hall Process: Electrolysis of Al 2 O 3 VERY ENERGY CONSUMING! VIDEO VIDEO
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4 The Hall Process: Electrolysis of Al 2 O 3 Cathode: 4 {Al 3+ + 3 e - Al (l)} Anode: 3 {2 O 2- + C (s) CO 2 (g) + 4 e - } Overall: 2 Al 2 O 3 + 3 C (s) 4 Al (s) + 3 CO 2 (g) KEY FACTOR: Al 2 O 3 has too high of a melting point (2020 o C), and the liquid is a poor electrical conductor. For electrolysis to be feasible, Al 2 O 3 is dissolved in molten cryolite, Na 3 AlF 6 (mp = 1000 o C, good electrical conductor).
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5 Copper: Ore to Metal Phase 3: Enriched ore (~25% copper) is smelted and refined CuO + C Cu + CO
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6 Sodium Hydroxide (Caustic Soda) NaOH 30 billion tons produced annually used in manufacture of paper, soaps, and other chemicals 2 NaCl (aq) + 2 H 2 O (l) 2 NaOH (aq) + Cl 2 (g) + H 2 (aq) electric current NaCl mine
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7 Why, Why, Why?
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8 Why, Why, Why? www.matcoinc.com
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9 Why, Why, Why?
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10 Potato-Powered Potato-Powered Clocks and Web Clocks and Web Server! Server! Each potato provides approximately 0.5 V of electricity: Electrochemistry!! Using potatoes, nails and pennies
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11 Recognizing Redox Reactions Recognizing Redox Reactions How do we know if electron transfer occurs in a reaction?? 2 Ca (s) + O 2 (g) 2CaO (s) Step 1: Step 1: Determine the oxidation number (or oxidation state) of each element in the reactants and products. Step 2: Step 2: If the oxidation state of a given element is different in the products than it is in the reactants, then electrons were transferred.
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12 Oxidation Numbers Oxidation Numbers 2 Ca (s) + O 2 (g) 2CaO (s) 0 0 +2 -2 Oxidation numbers are a mathematical tool for “dividing up” the electrons in a molecule. Element Initial Final Change ______ Ca 0 +2 Ca lost 2 electrons O 0 -2 O gained 2 electrons Gaining electrons cause oxidation number to decrease Losing electrons causes oxidation number to increase
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13 Rules for Assigning Oxidation Numbers (N Rules for Assigning Oxidation Numbers (N ox ox ) ) 1) The oxidation number, N ox , for a free elements free elements (not in a compound) is zero. e.g. Na N ox = 0 Mg N ox = 0 Al N ox = 0 2) The oxidation number of a monatomic ion monatomic ion (ion composed of only 1 atom) is equal to the ion charge: e.g. Na + N ox = +1 Mg 2+ N ox = +2 O 2- N ox = -2 Cl - N ox = -1
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14 3) The oxidation number of a group 1A group 1A element in a molecule is always +1 +1 e.g. NaCl N ox (Na) = +1 KClO 3 N ox (K) = +1 4) The oxidation number of a group 2A group 2A element in a molecule is
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CHM1311 - Lecture(14) - Electrochemistry (Redox Chemistry)...

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