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Chapter 23 & 24

Chapter 23 & 24. Potentiometry and Coulometry CHM 411 Spring 2013. I. Reference Electrode. It is the ½ cell potential that is known as a constant and completely insensitive to the composition of the solution under study. Saturated calomel electrode.

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Chapter 23 & 24

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  1. Chapter 23 & 24 Potentiometry and Coulometry CHM 411 Spring 2013

  2. I. Reference Electrode • It is the ½ cell potential that is known as a constant and completely insensitive to the composition of the solution under study

  3. Saturated calomel electrode 2 Hg2Cl2(s)+ 2e-↔ 2Hg (l) + 2Cl- E (sat’d KCl) = 0.241 V A. Calomel Electrodes

  4. Silver-Silver Chloride electrode AgCl (s) + e-↔ Ag(s) + Cl- E (sat’d KCl) = 0.179 V B. Ag/AgCl Electrodes

  5. II. Membrane indicator electrodes • ion selective electrodes

  6. II. Membrane indicator electrodes • pH electrodes

  7. B. Liquid Membrane Electrode Ca+2 ion selective electrode Ion exchanger in Ca+2 electrode is calcium didecylphosphate dissolved in diocylpphenylphosphonate [(RO)2PO2]2Ca ↔ 2(RO)2PO2- +Ca+2 where R = C10H21

  8. C. Crystalline ion-selective electrode Migration of F- through LaF3 doped with EuF2. A neighboring F-can jump into the vacancies and move the F- through the lattice and establishes the potential difference.

  9. D. Gas sensing probes

  10. III. Coulometry • Three electrochemical methods require no calibration against standards

  11. II. Types of Coulometric Methods A. Potentiostatic

  12. 1. Operation of a cell at a fixed potential • Simplest to perform, but has drawbacks

  13. 2. Current changes during electrolysis at constant applied potential • If potential is held at -2.5V the current is expected to decrease because of the depletion of the copper ions.

  14. 3. Potential changes during electrolysis

  15. B. Coulometric titrations • Employs a titrant that is electrolytically generated at a constant current

  16. C. Constant Current Electrolysis • The electrodeposition is carried out by maintaining a constant current

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