Computing the emf. E (and the related membrane potential EM) of the general concn. cell: electrode J|IJ (m1) in S| membrane I|IJ (m2) in S| electrode J (where the membrane permselective to counterion I separates 2 solns. of molalities m1 and m2 of the same electrolyte IJ, one mole of which forms nI mol of I of valency zI and nJ moles of coion J of valency ZJ with n = nI + nJ) requires integration between limits m1 and m2 of the differential equation: dE = [nRT/FnJ|zJ|][τIzI - mτsMs]dln(mγ)IJ, where the transference nos. τ1 of I and τS of the solvent S through the membrane are customarily taken as const. The key point is the integration of the term mdln (mγ), which in the current practice is oversimplified to give [(m1 + m2)/2]ln(m2γ2/m1γ1), and may cause large overestimation of the solvent-transfer contribution, with unreliable results for E and EM. The procedure recommended is instead that of slitting into the "ideal part" and the "non-ideal part", the latter being safely integrable putting lnγ as an explicit function of m in terms of the extended Debye-Hueckel equation. Alternative and equally reliable procedures are described.

Evaluating membrane cell emf from different schemes of integration of the relevant Nernstian equations / P. Longhi, P.R. Mussini, T. Mussini, S. Rondinini. - In: JOURNAL OF MEMBRANE SCIENCE. - ISSN 0376-7388. - 34:3(1987), pp. 345-353.

Evaluating membrane cell emf from different schemes of integration of the relevant Nernstian equations

P. Longhi
Primo
;
P.R. Mussini
Secondo
;
T. Mussini
Penultimo
;
S. Rondinini
Ultimo
1987

Abstract

Computing the emf. E (and the related membrane potential EM) of the general concn. cell: electrode J|IJ (m1) in S| membrane I|IJ (m2) in S| electrode J (where the membrane permselective to counterion I separates 2 solns. of molalities m1 and m2 of the same electrolyte IJ, one mole of which forms nI mol of I of valency zI and nJ moles of coion J of valency ZJ with n = nI + nJ) requires integration between limits m1 and m2 of the differential equation: dE = [nRT/FnJ|zJ|][τIzI - mτsMs]dln(mγ)IJ, where the transference nos. τ1 of I and τS of the solvent S through the membrane are customarily taken as const. The key point is the integration of the term mdln (mγ), which in the current practice is oversimplified to give [(m1 + m2)/2]ln(m2γ2/m1γ1), and may cause large overestimation of the solvent-transfer contribution, with unreliable results for E and EM. The procedure recommended is instead that of slitting into the "ideal part" and the "non-ideal part", the latter being safely integrable putting lnγ as an explicit function of m in terms of the extended Debye-Hueckel equation. Alternative and equally reliable procedures are described.
Settore CHIM/01 - Chimica Analitica
Settore CHIM/02 - Chimica Fisica
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/175472
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