engleski

Thermodynamic model of Charging the Gas/Water Interface

Charging of water layer at gas/water interface is analyzed experimentally and theoretically. Experimental data on the surface tension and on the surface potential in the acidic range are presented. Literature electrokinetic data indicate the isoelectric point of gas/water interface at pH 3.8. In the acidic region surface potential vs pH have a slope to be 55 % of the Nernstian. The surface tension exhibit minimum at pH 3.8. Thermodynamic model, based on distribution of ions between bulk and interface, is developed. The interpretation of surface and electrokinetic potential data provided equilibrium constants for distribution of ions between bulk and interface and the ionization equilibrium constant of interfacial water. Significantly higher ionization of interfacial water with respect to the bulk phase was observed. The affinity of hydrogen and hydroxide ions to be accumulated at the interface is higher with respect to the bulk of the solution which is more pronounced for hydroxide ions. The minimum of surface tension at the isoelectric point, is presented and analyzed. The thermodynamic concept, in accordance with the Gibbs isotherm, takes into account the variation of the composition at the interface. Effect of electrolytes on the surface tension, i.e. Jones-Ray effect, is also discussed.

gas/water interface; interfacial water layer; charge of interfacial water; surface tension; surface potential; thermodynamic equilibrium constants; Jones-Ray effect

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