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Daniell Cell: 1.10 volts Zn(s) + Cu 2+ ( aq ) → Zn 2+ ( aq ) + Cu(s)

Oxidation and Reduction, Electrochemistry Charles H. Mahler Pennsylvania Multi-Region STEM Grant Immaculata University July-August 2013.

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Daniell Cell: 1.10 volts Zn(s) + Cu 2+ ( aq ) → Zn 2+ ( aq ) + Cu(s)

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  1. Oxidation and Reduction, ElectrochemistryCharles H. MahlerPennsylvania Multi-Region STEM GrantImmaculata University July-August 2013

  2. Oxidation State (number) Rules1) Pure elements ox. states = zero2) Simple ions ox. states = charge3) H in compounds is usually +14) O in compounds is usually -25) Sum of all ox. states in molecules is zero, in complex ions equals ion charge6) Can use Periodic Table for other simple ox. states (Na +1, F -1, Mg +2)

  3. Daniell Cell: 1.10 voltsZn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) http://commons.wikimedia.org/wiki/File:Galvanic_cell_labeled.svg

  4. If A and B are opened together, water will flow from B to A. If A and C are opened together, water will flow from C to A. If D and E are opened together, water will flow from E to D. If F and B are opened together, water will flow from F to B. Instead of figuring out their exact heights, or listing all possible combinations, to predict the direction of flow all we need is to list these tanks by height:(Highest) E > F > B > C > A > D (Lowest) • Figure taken from and examples adapted from http://bouman.chem.georgetown.edu/S02/lect25/lect25.htm

  5. Standard Reduction PotentialsAll written as reductions, listed in order from highest voltage to lowest • Table taken from http://bouman.chem.georgetown.edu/S02/lect25/lect25.htm

  6. To make a cell, you need both an oxidation and a reductionThe standard potential (voltage) for a galvanic cell is just:Eocell = Eoreduction- Eooxidation

  7. Eocell = Eoreduction- EooxidationZn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)Cu2+ (aq)  +  2e-  Cu (s) 0.34 VZn2+ (aq)  +  2e-   Zn (s) –0.76 VEocell = 0.34 V – (–0.76 V) = 1.10 V

  8. Electrochemistry Vocabulary IGalvanic cell – has a positive potential (voltage) and is a spontaneous reaction, used to do electrical work / is a source of energy (an example is a battery)Anode – electrode where oxidation takes place in a galvanic cellCathode - electrode where reduction takes place in a galvanic cell

  9. Electrochemistry Vocabulary IIElectrolytic cell - has a negative potential (voltage) and is NOT a spontaneous reaction, consumes electrical work / needs an outside source of energy to run (an example is a battery being charged, or splitting water into hydrogen and oxygen)Galvanized – a metal (usually iron or steel) that has a layer of zinc (Zn) applied to prevent rusting has been galvanized. The zinc will oxidize before the iron will, protecting the iron.

  10. Rusting vs. Galvanized metal Left image: http://commons.wikimedia.org/wiki/File:Rust_1.jpeg Right image: http://commons.wikimedia.org/wiki/File:Feuerverzinkte_Oberfl%C3%A4che.jpg

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