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, 7 th ed", Chapter 17, p. 349-357 You have been given a copy of the reading from this additional reference.

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

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

4. Electrolysis and Mass Changes Example (p. 350, Harris 7 th 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? Harris, 7 th ed

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

6. Coulometry or Coulometric Titration analyte titrant generated at the anode from Br - Like electrolysis since both "pump" electrons into the cathode to cause reduction there. The solution initially contains Br -. At the anode (oxidation) the Br 2 is generated by oxidation of Br - 2 Br - → Br 2 + 2e - As soon as Br 2 is produced, it reacts with the C 6 H 10 When all the C 6 H 10 is consumed, the excess Br 2 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 C 6 H 10 are calculated from the current and the time to the endpoint. Harris, 7 th ed

7. Br 2 generated here by oxidation of Br - C 6 H 10 reduced here to trans-1,2- dibromocyclohexane Harris, 7 th ed

8. Example (p. 356, Harris 7 th 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?