AgX Ag Research Articles

Towards a model of silver halide-silver oxysalt glassy electrolytes

Conductometric, spectroscopic, dynamical, diffractometric studies of AgXAg 2OB 2O 3 and AgXAg 2OP 2 O 5 (with X = I, Br, Cl) glassy electrolytes are reviewed. While it is universally accepted that silver halide is the main component responsible for the conduction properties, AgX crystalline cluster models do not seem able to account for all the experimental observations. It is suggested that an adequate model could be based on AgX amorphous clusters, that is, nearly structureless agglomerates of Ag and X atoms.

Structure and ionic conductivity of glasses in the ternary systems AgX(X = I, Br or Cl) [sbnd]Ag 2O [sbnd]B 2O 3

Superionic conducting glasses in the ternary systems AgX Ag 2O B 2O 3 have been prepared for AgX=AgI, AgBr or AgCl. Glass-forming regions, glass transition temperatures, IR spectra, conductivities and transport numbers of Ag + ions and electrons were determined for these glasses. The glasses were composed of BO 3, BO 4 and B-O-B groups regardless of their compositions, and in addition BO 3X groups were shown to be present in the glasses with the Ag 2O/B 2O 3 mole ratio larger than unity. The conductivities, ranging from 10 −2 to 10 −7 ω −1 cm −1 at 25°C, showed small difference for glasses in the three systems containing the same amounts of AgX, Ag 2O and B 2O 3. A structure model explaining the Ag + ion transport is proposed.

Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part 17.—Free energies of transfer of alkali-metal chlorides from water to 10–40 %(w/w) dioxan + water mixtures, and of potassium bromide and iodide to the 20 % mixture, at 25°C

The cell Ag–AgX | MX(ms), S | M(Hg)| MX(mw), W | AgX–Ag, has been used to determine the standard molar free energies of transfer, ΔG°t, of the alkali-metal chlorides from water to 10, 20 and 40 %(w/w) dioxan + water mixtures and of potassium bromide and iodide to the 20 % mixture. Results from an earlier Part showing ΔG°t for the transfer from water to 20 % dioxan for the alkali-metal chlorides to be linear with respect to the reciprocal of cation radius are withdrawn. Instead it is found for all transfers, as in the methanol + water system, that ΔG°t(Li+Cl–) < ΔG°t(Na+Cl–) but that ΔG°t(Rb+Cl–) > ΔG°t(Cs+ Cl–); this is explained in terms of the “acid-base” theory of ionic solvation. Tests of additivity show the new data to be highly consistent with previous work.

Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part 16.—Free energies of transfer of sodium bromide and iodide from water to 10–99%(w/w) methanol + water mixtures at 25°C

The cell Ag—AgX|Na(ms), S|Na(Hg)|NaX(mw), W|AgX—Ag has been used to determine the standard molar free energies of transfer, ΔG°, of sodium bromide and iodide from water, W, to 10–99%(w/w) methanol + water mixtures, S. The results are compared with those previously obtained from cells with hydrogen electrodes; in general the ΔG°t-values for the sodium halides are highly consistent with those for the hydrogen halides. For sodium iodide, ΔG°t is highly inflected in the structurally critical region of solvent composition.

Studies in ‘isodielectric’ media. Part I. Standard potentials of Ag–AgX (X = Cl or Br) electrodes in methanol–propylene glycol at 25 °C

Standard potentials (sE°) of the Ag–AgCl and Ag–AgBr electrodes have been determined in a series of approximately ‘isodielectric’ media, formed by mixing methanol (Ds= 32·63) and propylene glycol (Ds= 31·0) in various proportions at 25°, from the e.m.f. measurements of the cell: Pt, H2(g, 1 atm)|HCl(m), solvent|AgCl–Ag and Pt, H2(g,1 atm)|HOAc(m1), NaOAc(m2), NaX(m3), solvent|AgX–Ag, where X = Br. The required p(sKa)HOAc values for the latter were determined from the same type of cell with X = Cl. The molal activity coefficients (ssγ)HCl of HCl, referred to the standard state in each solvent mixture, have been evaluated at different concentrations (0·005—0·07m), and are found to vary only slightly from solvent to solvent at any concentration, as expected from the small difference in dielectric constants of the solvents. The standard free-energy changes ΔGt°(HX) accompanying the transfer of 1 mole of HX from methanol to the other solvent have been computed, and are found to decrease some–what sharply at first but less so as the proportion of propylene glycol increases. The relative magnitudes of ΔGt°(HX) for both HCl and HBr indicate that anions are glycophilic and that H+ is methanophilic, suggesting that methanol is more ‘basic’ than propylene glycol.

Studies in some ‘isodielectric’ media. Part III. Standard potentials of M/M+(M = Li, Na, and K) electrodes in methanol–propylene glycol

Standard potentials (sE°) of M/M+(M = Li, Na, or K) electrodes have been determined at 25° in the ‘isodielectric’ methanol–propylene glycol solvent system from the measured e.m.f. values of the cell My(Hg)/MBr(m), solvent/AgBr–Ag. These potentials as well as the known (sE°) values of the AgX–Ag (X = Cl or Br) electrode furnished the standard potentials (sEcell°) of the complete cells comprising the M/M+ and AgX–Ag electrodes. The standard free-energy changes ΔGt°(MX) accompanying the transfer of MX from methanol to the other solvents have been computed and are found to depend chiefly on the ion–dipole interactions, as the ‘electrostatic effect’ is relatively small in this solvent system. The values of ΔGt°(i) for the individual ions, computed from the ‘simultaneous extrapolation’ of the observed linear plots of ΔGt°(MCl) and ΔGt°(KCl–MCl) against (rM+)–1(M = Li, Na, or K), to (rM+)–1= 0, suggest that the cations are methanophilic and that the anions are glycophilic. The variation of ΔGt°(i) values with the solvent composition is found to be in fairly good agreement with what is expected from the consideration of the interaction energies of these ionic species with positive or negative charge centres of the isolated solvent dipoles. Also the values of ΔGt°(H+) for H+ seem to indicate that methanol is more ‘basic’ than propylene glycol.

Standard E.m.f.s of the cells H2|HX|AgX–Ag (X = Cl, Br, or I) in 20 and 40%(w/w) dimethyl sulphoxide–water mixtures at 25°C

Standard molal e.m.f.s at 25°C of the cells H2|HX|AgX–Ag (X = Cl, Br, or I) in 20 and 40%(w/w) dimethyl sulphoxide–water mixtures are reported. Lightly platinised hydrogen electrodes proved highly satisfactory and no special technique was required in their preparation.

The standard potentials of silver–silver halide electrodes and ion solvation in dimethyl sulphoxide–water mixtures at 25 °C

Standard e.m.f.s of the cells H2|HX|AgX–Ag (X = Cl, Br, or I) in 10, 60, 70, and 80%(w/w) dimethyl sulphoxide–water mixtures are reported. These, together with values for mixtures of other compositions determined earlier, were used to calculate the molar free energies of transfer of the halogen acids from water to the mixed solvents. Single-ion values were derived therefrom by use of the extrathermodynamic assumptions of Feakins et al. and discussed in terms of ion solvation. It is shown that the solvophilicity of the ions is largely determined by their acid–base' interactions with the solvent molecules. The structural features of the solvents are briefly discussed.

Microdetermination of trace quantities of organic chloride by combustion and microcoulometry: Application to low-boiling liquids

Methods for the determination of trace amounts of chloride in organic materials include procedures based on the reaction with sodium biphenyl reagent, the ASTM wick lamp combustion, and modifications of the tube combustion for the decomposition of the organic material. Methods utilizing potentiometric, amperometric, or colorimetric techniques have been reported to measure the chloride in the combusted material. Summaries of these methods are given in subsequent sections of this report. In addition to these methods we have applied a combustion tube technique utilizing a microcoulometric titration to determine trace chlorides in low-boiling organic liquids (kerosene range). This method is based on the work of Coulson et al. ( 3). It is possible by this technique to complete an analysis in 3–5 minutes as opposed to between 1–3 hours by the other methods. Preliminary results indicate comparable precision. In the analysis, a sample (up to 5 μl) is injected into a vaporization chamber and carried with nitrogen to the combustion zone which is maintained at 800 °C. The nitrogen flow is mixed with oxygen and passes through the combustion tube into the titration cell. The chloride is titrated according to the following reactions: Ag ++X−→ AgX Ag°→ Ag ++ e and the area of the recorded peak measured. Investigation will be carried out to expand the method to include high boiling liquids and solids.

Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part V. The halogen acids in 10, 20, 40, and 60%(W/W) acetic acid–water mixtures at 25°

Standard e.m.f.s. have been obtained for the cells H2|HX|AgX–Ag (X = Br or I) in 10, 20, 40, and 60%(W/W) solutions of acetic acid in water. Some measurements were made by a new rapid technique. Molar free energies of transfer, ΔGt°, from water to the mixtures, of HCl, HBr, and Hl, have been calculated. These have been split into contributions from the ion constituents by the method described earlier in this Series. The proton is in higher free-energy states in the mixtures than in comparable methanol– or dioxan–water mixtures and, probably, than in pure water. The anions are in lower free-energy states in the mixtures than in the methanol– and dioxan–water mixtures, though not than in water. These findings are generally in accord with the theory of ion solvation developed earlier.

918. Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part III. The cell H2|HX|AgX–Ag (X = Br or I) in 20 and 45% mixtures of dioxan and water at 25°

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897. Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part I. The cell H2|HX|AgX–Ag (X = Br,I) in 10% and 43.12% mixtures of methanol and water

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