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Ch 17: Instrumental Methods in Electrochemistry

Ch 17: Instrumental Methods in Electrochemistry. Principle parts of a personal glucose monitor (covered in the section on Amperometry). The following chapter material is taken from your text and another textbook by Harris:

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Ch 17: Instrumental Methods in Electrochemistry

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  1. Ch 17: Instrumental Methods in Electrochemistry Principle parts of a personal glucose monitor (covered in the section on Amperometry) The following chapter material is taken from your text and another textbook by Harris: Daniel C. Harris, "Quantitative Analysis, 7th ed", Chapter 17, p. 349-357 You have been given a copy of the reading from this additional reference.

  2. - + Fundamentals of Electrolysis Electrolysis is the process in which electrical energy is used to cause a nonspontaneous chemical reaction to occur by "pumping" electrons into the cathode. 2 Na+ + 2 Cl-→ 2 Na(l) + Cl2(g) Eo = - 4.075 +4.075 is the minimum voltage that must be applied to the cathode to reduce Na+

  3. Cathode: Cu2+ + 2e- = Cu(s) Anode: H2O = ½ O2(g) + 2 H+ + 2e- Net: H2O + Cu2+ = Cu(s) + ½ O2(g) + 2 H+ Current (I) is measured in Coulombs second Coulombs = Coulombs x seconds second q = I x t Conversion between moles e- and Coulombs is Faraday's constant: 1 mole e- 96,500 C Harris, 7th ed

  4. Electrolysis and Mass Changes Harris, 7th ed Example (p. 350, Harris 7th ed): If a current of 0.17 A flows for 16 min through the cell in Figure 17-1, how many grams of Cu(s) will be deposited?

  5. Electrogravimetric Analysis Harris, 4th ed Practical application of electrolysis: reduce a metal at the cathode, and weigh the mass of the cathode before and after the reaction. Cu2+(aq) + 2e-→ Cu(s) deposited on cathode (Pt gauze)

  6. Coulometry or Coulometric Titration Harris, 7th ed titrant generated at the anode from Br- analyte • Like electrolysis since both "pump" electrons into the cathode to cause reduction there. • The solution initially contains Br-. At the anode (oxidation) the Br2 is generated by oxidation of Br- • 2 Br-→ Br2 + 2e- • As soon as Br2 is produced, it reacts with the C6H10 • When all the C6H10 is consumed, the excess Br2 generated at the anode signals the end of the titration (solution turns orange-brown and the detector electrodes voltage reaches a maximum) • The moles of C6H10 are calculated from the current and the time to the endpoint.

  7. Harris, 7th ed Br2 generated here by oxidation of Br- C6H10 reduced here to trans-1,2-dibromocyclohexane

  8. Harris, 7th ed Example (p. 356, Harris 7th ed): A 2.000 mL volume containing 0.6113 mg of cyclohexene/mL is to be titrated in Figure 17-8. With a current of 4.852 mA, how much time is required for complete titration?

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