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Electrochemistry / Redox
Day 3: Utilizing Redox Reactions
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Balancing Practice Balance the following redox reaction: Au+3(aq) + I-1(aq) Au(s) + I2(s) Balance the following redox reaction, which takes place in an acidic solution: MnO4- + S2O3-2 Mn+2 + S4O6-2 Balance the following redox reaction, which takes place in a basic solution: Zn + NO3- Zn(OH)4-2 + NH3
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Simple Voltaic Cells (Galvanic Cells)
Cu + 2Ag+ 2Ag + Cu2+ voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag If the reaction is spontaneous … Salt bridge e- Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag If the reaction is spontaneous … Salt bridge e- Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag If the reaction is spontaneous … e- Salt bridge e- Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- If the reaction is spontaneous … e- Salt bridge e- Na+ NO3- electrode electrode Mass of electrode decreases, [Cu2+] increases Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- If the reaction is spontaneous … e- Salt bridge Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- e- If the reaction is spontaneous … Salt bridge Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- e- If the reaction is spontaneous … Salt bridge Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- e- If the reaction is spontaneous … Salt bridge Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- e- If the reaction is spontaneous … Salt bridge Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- e- If the reaction is spontaneous … Salt bridge Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- e- If the reaction is spontaneous … Salt bridge Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag e- e- If the reaction is spontaneous … Salt bridge e- Na+ NO3- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag If the reaction is spontaneous … Salt bridge e- Na+ NO3- e- e- electrode electrode Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag If the reaction is spontaneous … Salt bridge Na+ NO3- e- e- electrode electrode e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag If the reaction is spontaneous … Salt bridge Na+ NO3- e- electrode electrode e- e- Mass of electrode increases, [Ag+] decreases Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag If the reaction is spontaneous … Salt bridge Na+ NO3- e- electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge NO3- Na+ e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge NO3- Na+ e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Cu + 2Ag+ 2Ag + Cu2+ Cu Cu2+ + 2e- 2e- +
voltmeter Cu Cu2+ + 2e- wire 2e- + 2Ag+ 2Ag negative charge If the reaction is spontaneous … Salt bridge Na+ NO3- e- The salt bridge allows for a complete circuit so the electrons can move electrode electrode e- e- Cu metal Ag metal Cu(NO3)2 soln AgNO3 soln Half cell Half cell
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Simple Voltaic Cells Important Points: Cu + 2Ag+ 2Ag + Cu2+
Cu Cu2+ + 2e- 2e- + 2Ag+ 2Ag Important Points: 1. The electrode where the oxidation takes place is called the ANODE (negative electrode) 2. The electrode where the reduction takes place is called the CATHODE (positive electrode) 3. Electrons always flow from the anode to the cathode in a voltaic cell.
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Simple Voltaic Cells Important Points: Cu + 2Ag+ 2Ag + Cu2+
Cu Cu2+ + 2e- 2e- + 2Ag+ 2Ag Important Points: 4. Notation for electrochemical cells: Cu(s) │Cu2+ │ │ Ag+ │ Ag(s) anode Salt bridge cathode
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Voltaic Cells with Inert Electrodes
H Fe+3 2Fe H+ H2 2H+ + 2e- 2e- + 2Fe+3 2Fe+2 When the reactants and products CAN NOT be used as electrode materials, other, chemically inert substances must be used Pt Fe+2 H+ H+ Fe+3 - Graphite, mercury, platinum, gold, etc.
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Voltaic Cells with Inert Electrodes
H Fe+3 2Fe H+ H2 2H+ + 2e- 2e- + 2Fe+3 2Fe+2 Write the shorthand notation for the cell shown to the right. Pt H2 │H+ │ │ Fe+3 │ Fe+2 Fe+2 Fe+3
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Voltaic Cells with Inert Electrodes
Suggested homework for this weekend: 1-2 hours of AP Test Prep Practice several redox balancing problems (regular, acidic and basic solution problems)
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Alkaline Batteries e- Zn(s) + 2OH-1 ZnO + H2O(l) + 2e-
(salt bridge) 2MnO2(s) + H2O(l) +2e- Mn2O3 + 2OH- e-
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Simple Voltaic Cells Describe how to set up a voltaic cell using the following reaction: Fe + Cu2+ Cu + Fe2+ Consider: 1. Which electrode is anode? 2. Which is cathode? 3. Direction of e- flow? 4. Direction of ion flow? 5. Which half reaction occurs where? 6. Which electrode is increasing in mass? 7. How are the [ion] changing? 8. What notation would describe this cell?
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