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Amperometry, Coulometry, Aquametry I. Current = charge/unit time. Charge = integral of currents. Amperometry: current proportional to instantaneous flux of analyte to electrode. Coulometry: charge proportional to total amount of analyte. Aquametry: coulometry used to quantify water (Karl Fischer titration). II. If current constant, Q = i*t. Faraday constant = ratio of charge (in Coulombs) to moles = 96485.383. III. Ohmic drop, concentration polarization, and overpotential mean E applied > E Nernst . Use of 3 electrode systems to compensate for overpotential. Electrolysis never 100% complete (would require infinite potential and time). So choose % completion desired. IV. Determination of water in grain: near-infrared absorption spectrometry OR Karl Fischer titration. CH 3 OH + SO 2 + pyridine pyridinium + + CH 3 OSO 2 - CH 3 OSO 2 - + H 2 O + I 2 + 2 pyridine 2 pyridinium I - + CH 3 OSO 3 - Generate I 2 by electro-oxidation of I - . Complications: stray water in reactants and on glassware. Conductivity end-point a problem in
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Quant_Lect_11_Amp - Untitled Document Page 1 of 2...

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