Paolo Longhi

Reference value standards for pH measurements in 5, 15 and 30% (w/w) acetonitrile/water solvent mixtures at temperatures from 288.15 to 308.15 K

Abstract Reference value standards, pH (RVS), for 0.05 mol kg −1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 5, 15 and 30% (w/w) acetonitrile/water mixed solvents at temperatures from 288.15 to 308.15 K are determined from reversible e.m.f. measurements of the cell Pt¦H 2 ¦KHPh + KCl¦AgCl|Ag|Pt. Values of the first ionisation constant of o -phthalic acid (H 2 Ph; benzene-1,2-dicarboxylic acid) in these mixed solvents are also determined from analogous measurements. The consistency of the results is analysed by multilinear regression of the quantity p( a HγCl ) as a function of both solution composition and temperature. The standard pH (RVS) values determined are given by the equation pH (RVS) = 4.0080 + 6.330 x + 16.177 x 2 − 115.3 x 3 + 0.3089 u − 201.0 ux 2 + 909 ux 3 + 13.04 v , where x is the mole fraction of acetonitrile in the mixed solvent, u = z /(1 + z ), v = [ln(1 + z ) − u ], z = ( T − θ)/θ, and θ = 298.15 K.

Determination of standard pH values for potassium hydrogen phthalate reference buffer solutions in 10, 20, 50, 64 and 84.2 wt per cent methanol/water mixed solvents at temperatures from 283.15 to 313.15 K

Abstract Standard pH 0 values for 0.05 mol kg −1 potassium phthalate reference buffer solutions in 10, 20, 50, 64 and 84.2 wt % methanol/water solvent mixtures have been obtained from cells without transport, in the temperature range 283.15–313.15 K. The consistency of results has been analysed by a new method of multilinear regression of the quantity p( a H γ Cl ) as a function of both temperature and solution composition. The pH° values found can be reproduced within ± 0.01 by the equation pH 0 = 4.00 + 4.38 x − 5.02 x 2 + 4.23 x 3 + 0.13 z − 0.91 xz , where x = mole fraction of methanol in the solvent mixture, z = ( T − θ)/θ and θ = 298.15 K. Subsidiary values of the first ionization constant of o -phthalic acid in the above solvent mixtures have also been obtained by the buffered cell method.

Thermodynamics of the cell H2/HCl/AgCl/Ag in (acetonitrile + water) solvents☆

Abstract The standard e.m.fs ( p o = 101325 Pa) for the cell H 2 /HCl/AgCl/Ag in (acetonitrile + water) containing mass percentages of acetonitrile from 0 to 50 have been obtained as a function of mole fraction x of acetonitrile and temperature (within the range from 288.15 to 308.15 K), using a one-stage multilinear regression method applied to the analysis of experimental e.m.f.s. Thermodynamic functions ( ΔG m o , ΔH m o , ΔS m o , and ΔC p , m o ) for the cell reaction at T = 298.15 K have also been obtained as functions of x . A comparison is made with the corresponding quantities computed from separate analyses of e.m.f.s for each experimentally investigated solvent composition (mass percentages of acetonitrile: 0, 5, 10, 15, 30, and 50).

Standard pH values for potassium hydrogenphthalate reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water mixed solvents at temperatures from 288.15 to 318.15 K

Abstract Standard pH(S) values for 0.05 mol kg −1 potassium hydrogenphthalate (KHpH) reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water solvent mixtures within the temperature range 288.15–318.15 K are determined from e.m.f. measurements of the cell without transference Pt|H 2 |KHPh + KCl|AgCl|Ag|Pt. The consistency of the results is analysed by a recently described method of multilinear regression of the quantity p( a H γ Cl ) as a function of both solution composition and temperature. The standard pH(S) determined can be reproduced to within ±0.01 by the equation pH(S) - 4.004 + 3.309 w + 0.408 z + 1.037 w 3 - 14.95 zw 2 + 27.1 zw 3 , where w is the weight fraction of dioxane in the solvent mixture, z = ( T – θ )/ θ , and θ - 298.15 K. Values of the first ionization constant of phthalic acid (H 2 Ph; benzene-1,2-dicarboxylic acid) in the above solvent mixtures are also determined from e.m.f. measurements of the cell without transference Pt|H 2 |H 2 Ph + KHPh + KCl|AgCl|Ag|Pt.

Electrochemistry of the biliverdin—bilirubin system in N,N-dimethylformamide

Abstract The electrochemical behaviour of biliverdin and bilirubin on platinum electrodes in N, N-dimethylformamide has been investigated by means of voltammetric as well as controlled-potential electrolysis techniques. Bilirubin can be oxidized to biliverdin and the latter, in turn, to further oxidation products; conversely, biliverdin can be reduced to bilirubin, and the latter to further reduction products: however, the potential for the anodic oxidation of bilirubin to biliverdin and that for the cathodic reduction of biliverdin to bilirubin are about 1.6 V apart from each other. The reduction of biliverdin to bilirubin is shown to be amenable to preparative electrochemistry.

Use of amalgam concentration cells for determination of transference numbers in solid electrolytes—I. Electronic transference numbers of β-aluminas

The determination of transference numbers for different doped as well as undoped sodium-β-aluminas has been carried out by means of a method based on emf measurements of amalgam concentration cells of the type Nax2Hg1−x2/sodium-β-alumina/Nax1Hg1−x1 at 25°C. The details of this method, whose validity extends also to cationic conducting solids other than β-aluminas, are described and discussed for comparison with the results of previous investigations.

Ion and solvent transfers at homoionic junctions between concentrated electrolyte solutions

A unified treatment of liquid junction potentials and membrane potentials which accounts for both ionic and solvent transfers at homoionic junctions between ultra concentrated electrolyte solutions, also in terms of the primary hydration parameters and the Stokes-Robinson hydration theory, is described. Application to the determination of cation transference numbers, τ+, water transference numbers, τw, and primary hydration numbers,h, is described as a rational scheme for characterization of concentrated electrolytes as possible new salt bridges for the minimization of liquid junction potentials in electroanalysis. Examples of application of this scheme are presented based on multiple regression analysis of electromotive force measurements of such homoionic concentration cell as Ir | Cl2 | HCl (m2) ‖ HCl (m1) | Cl2 | Ir and Hg | Hg2SO4 | Li2SO4 (m2) ‖ Li2SO4 (m1) | Hg2SO4 | Hg, with fixedm1 molality and variedm2 molality. Based on the electromotive force of analogous homoionic transference cells but with interposed membranes, application of the present procedure can be extended to the determination of ion and solvent transport parameters, notably the degree of permselectivity, of membranes for use either as selective sensors in electroanalysis or selective separators in industrial electrochemistry.

Standard potentials of the strontium amalgam electrode, and thermodynamics of the dilute strontium amalgams

Abstract From e.m.f. measurements of the cell: Pt|xSr + (1 − x)Hg|SrCl 2 (aq,m)|AgCl|Ag|Pt the standard potentials of the strontium amalgam electrode have been determined over the temperature range 283.15 to 343.15 K. The results can be reproduced accurately by the equation: E ° /V =−1.448013 −2.289353T/K + 2.582182 x 10−6(T/K) 2 The standard thermodynamic functions at 298.15 K for the strontium amalgam and for the strontium amalgamation reaction have been obtained. Also, the mean molar activity coefficients of SrCl 2 (aq) have been determined over the temperature range 283.15 to 343.15 K at molalities up to 0.3 mol kg −1 . The logarithm of the rational activity coefficient of strontium in dilute amalgams is a linear function of the mole fraction of strontium: log 10 f Sr = Qx Sr where Q is temperature-dependent and can be represented by the equation: Q = 541.347 − 2.2805(T/K) + 3.95021 X 10 −3 (T/K) 2 The values of Q obtained from the e.m.f. measurements of the above cell have been confirmed from supplementary e.m.f. measurements of the amalgam concentration cell: Pt| x 2 Sr + (1 − x 2 )Hg|SrCl 2 (non-aqueous)|x 1 Sr + (1 − x 1 )Hg|Pt over the same temperature interval.

Reference value standards for pH measurements in 10, 30, 50, and 70% (w/w) 2-propanol/water solvent mixtures at temperatures from 288.15 to 318.15 K

Abstract Reference value standards, pH (RVS), for 0.05 mol kg−1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 10, 30, 50 and 70% (w/w) 2-propanol/water solvent mixtures at temperatures from 288.15 to 318.15 K are determined from reversible e.m.f. measurements of the cell Pt¦H2¦KHPh + KCl¦AgCl¦Ag¦Pt. The consistency of the present results is confirmed by multilinear regression analysis of the pH values obtained for each solution composition and temperature, allowing appropriate interpolation of pH (RVS) values within the range of the experiment. The ancillary values of the standard e.m.f. of the cell Pt¦H2¦HCl¦AgCl¦Ag¦Pt are optimized through multilinear regression analysis of the available data in the literature, and the ancillary values of the first ionization constant of o-phthalic acid (H2Ph; benzene-1,2-dicarboxylic acid) in these solvent mixtures are evaluated from reversible e.m.f. measurements of the cell Pt¦H2¦H2Ph + KHPh + KCl¦AgCl¦Ag¦Pt.

Thermodynamics of the Cl2/Cl−/Cl3− system in aqueous solution

Summary A new method using e.m.f. measurements of the cell, H2, I atm |HCl, I M| Cl2, p atm, combined with measurements of chlorine solubility in I M HCl is described for determining the standard potentials of the chlorine electrode and the equilibrium constants for the reactions, Cl2(gas)+Cl−(aq.)=Cl3−(aq.) and Cl2(aq.)+Cl−(aq.)=Cl3−(aq.) over the range 25–80°. The standard thermodynamic functions for the species relevant to the Cl2/Cl−/Cl3− system have been derived from the results.