15-Redox_5_web - Redox titration A typical potentiometric...

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Unformatted text preview: Redox titration A typical potentiometric experimental set up for redox titration The potential of the working (or an indicator ) electrode is measured vs. a reference. The indicator electrode is usually a Pt wire immersed in solution containing the analyte. In potentiometry, the cell voltage, E, is the analytical signal. i i V V Powe r supply Powe r supply Working electrode Auxiliary electrode Working electrode Reference electrode Reference electrode Two-electrod e cell Thr ee-el ectrod e cell The standard potentials of Ce 4+ /Ce 3+ is 1.61 V, and the standard potential of Fe 3+ /Fe 2+ is 0.771 V. Whether or not a redox reaction is driven in a homogeneous or heterogeneous configuration, that is, whether or not electrons are moving in a platinum wire or directly from one ion (species) to another in solution, does not change the chemistry involved. In potentiometry , a potential of the working ( or an indicator ) electrode is measured vs. a suitable reference, tracking the Nernst equation! The x 0 approximation ; Nernsts equations REDOX TITRATION POTENTIOMETRY VOLTAMMETRY COULOMETRIC TITRATION POLAROGRPAHY Harris, pp. 340 - 392 Cathode: a Ox(1) + ne b Red(1) (1) Anode: c Ox(2) + ne d Red (1') n is common for the cathode and anode. E cathode E cathode o RT nF Ox a d b = + 2 303 1 1 . log [ ( )] [Re ( )] E anode E anode RT nF Ox c d d = + 2 303 2 2 . log [ ( )] [Re ( )] The Nernst equations (for half-reactions): R = 8.3143 (J K-1 mol-1 ), T: absolute temperature The reaction is however in equilibrium: Ce 4+ + Fe 2+ Ce 3+ + Fe 3+ (2) E E cathode o E anode o n products reac ts =-- 0 0592 . log [ ] [ tan ] The x 0 approximation Ce 4+ + Fe 2+ Ce 3+ + Fe 3+ (1) Ce 4+ + Fe 2+ Ce 3+ + Fe 3+ (1') x 0 approximation in redox titration The reaction is however in equilibrium: Ce 4+ + Fe 2+ Ce 3+ + Fe 3+ (2) ]...
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15-Redox_5_web - Redox titration A typical potentiometric...

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