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An Introduction to Electroanalytical Chemistry

Electrochemistry : The study of the interchange of chemical and electrical energy Oxidation i s the l oss of electrons (Increase in charge). Reduction i s the g ain of electrons (Decrease in charge). An Introduction to Electroanalytical Chemistry. Electrochemical Cells :. Galvanic Cells:

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An Introduction to Electroanalytical Chemistry

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  1. Electrochemistry: The study of the interchange of chemical and electrical energy Oxidationis the loss of electrons (Increase in charge). Reductionis the gain of electrons (Decrease in charge) An Introduction to Electroanalytical Chemistry Electrochemical Cells: • Galvanic Cells: • Produces electrical current • spontaneous chemical reactions •  Battery • 2. Electrolytic Cells • Consumes electrical current • non-spontaneous and require external e-source • (DC power source) • Cu2+ + 2e-Cu E0 = +0.34 V • Zn2+ + 2e- Zn E0 = −0.76V Cu2+ + Zn Cu + Zn2+ E0 = 0.34 – (-0.76) = 1.10 V Zn2+ + Cu  Zn + Cu2+ E0 = - 1.10 V

  2. Parts of the voltaic or galvanic cell… Anode  the electrode where oxidation occurs After a period of time, the anode may appear to become smaller as it falls into solution. Cathode  the anode where reduction occurs After a period of time it may appear larger, due to ions from solution plating onto it. Salt Bridge  a device used to maintain electrical neutrality in a galvanic cell This may be filled with agar which contains a neutral salt or it may be replaced with a porous cup. Electron Flow  always from anode to cathode (through the wire)

  3. Cathode Anode

  4. The diagram to the right illustrates what really happens when a Galvanic cell is constructed from zinc sulfate and copper (II) sulfate using the respective metals as electrodes.

  5. Electrolytic cells Electrolysis of molten sodium chloride •  None spontaneous reaction converted to spontaneous reaction •  Electrical energy converted into chemical energy Conduction in Electrochemical cells: a. External connection  Movement of electrons through the external wire. b. Within the solution  migration of cations and anions c. At the electrode surface  Oxidation/Reduction reaction

  6. A simplified drawing of a membrane cell for the production of NaOH and Cl2 gas from a saturated, aqueous solution of NaCl (brine).

  7. Consider electrolysis of aqueous NaCl. The process become complex in the presence of water as the water itself can be oxidized or reduced. Cathode – H2 is released Anode – O2 is released for dilute NaCl Cl2 is released for conc. NaCl Experimental results

  8. Cathodes and Anodes • Cathode of an electrochemical cell is the electrode at which reduction occurs • Anode of an electrochemical cell is the electrode at which oxidation

  9. e- V e- Zn Cu Zn2+ Cu2+ NO3- NO3- Standard Cell Notation (line notation) • Conventions: • Anode on Left • Single line : represent phase boundaries • Two line : represent liquid junction Anode / anode solution // cathode solution / Cathode Example: Zn / Zn2+ (1.0 M) // Cu2+ (1.0M) / Cu

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