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| - Adsorption of Atmospheric Gases at the Air−Water Interface. 4: The Influence of Salts
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| - We have measured the standard free energies and standard enthalpies of adsorption as well as saturated surfacecoverages for hexanoic acid and 1-propanol adsorbed at the air−aqueous interface of sodium chloride (NaCl)and ammonium sulfate ((NH4)2SO4) solutions of concentrations between 0 and 4 mol L-1. Temperature-dependent surface tension measurements are used to obtain ΔG0aq→σ and ΔH0aq→σ; using known Henry's lawconstants and estimated values of the salting-out coefficient we calculate the gas−interface adsorptionparameters ΔG0g→σ and ΔH0g→σ. A small (∼1−2 kJ mol-1) decrease in ΔG0aq→σ with increasing saltconcentration is accompanied by an increase (∼10−30%) in saturated surface coverage, consistent with theexpected “salting-out” behavior. Adsorption from the gas phase becomes somewhat less favorable withincreasing salt concentration for both organic species. The standard enthalpy of adsorption from the gas phasedecreases with increasing salt concentration for hexanoic acid, but not for 1-propanol. This may be aconsequence of acid dimer formation at the interface becoming important at higher coverages.
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